Be able to explain: 能够解释：
the trends in melting and boiling temperatures of the elements of Periods 2 and 3 of the Periodic Table in terms of the structure of the element and the bonding between its atoms or molecules; 元素周期表 2 和 3 周期元素的熔化和沸腾温度趋势，包括元素的结构及其原子或分子之间的键合;
the specific trends in ionisation energy of the elements across Periods 2 and 3 of the Periodic Table. 元素周期表第 2 周期和第 3 周期中元素电离能的具体趋势。
WHAT ARE PERIODIC PROPERTIES? 什么是周期性属性？
The elements in a period exhibit periodic properties (also sometimes called periodicity). 周期中的元素表现出周期性 （有时也称为周期性） 。
We can illustrate the idea of periodic properties by looking at the elements in Periods 2 and 3. We have already seen one example of periodic properties in Periods 2 and 3 - the regular repeating pattern of electronic configurations from ns^(1)\mathrm{ns}^{1} through to ns^(2)np^(6)\mathrm{ns}^{2} \mathrm{np}{ }^{6}. Other examples are the trends in atomic radii, melting and boiling temperatures, and first ionisation energies. 我们可以通过查看周期 2 和 3 中的元素来说明周期性的概念。我们已经在周期 2 和 3 中看到了周期性特性的一个例子 - 从 ns^(1)\mathrm{ns}^{1} 到 的 ns^(2)np^(6)\mathrm{ns}^{2} \mathrm{np}{ }^{6} 电子构型的规则重复模式。其他例子是原子半径、熔化和沸腾温度以及第一电离能的趋势。
ATOMIC RADII 原子半径
The atomic radius of an element is a measurement of the size of its atoms. It is the distance from the centre of the nucleus to the boundary of the electron cloud. Since the atom does not have a well-defined boundary, we can find the atomic radius by determining the distance between the two nuclei and dividing it by two. 元素的原子半径是其原子大小的量度。它是从原子核中心到电子云边界的距离。由于原子没有明确定义的边界，我们可以通过确定两个原子核之间的距离并将其除以 2 来找到原子半径。
fig A Measuring (a) the covalent radius and (b) the van der Waals radius. 图 A 测量 （a） 共价半径和 （b） 范德华半径。
Diagram (a) in fig A shows two bonded atoms. The atoms are closer together than they are in diagram (b) (where they are only just touching). 图 A 中的图 （a） 显示了两个键合原子。原子比图 （b） 中的原子靠得更近（其中它们只是刚刚接触）。
In diagram (a), we are measuring the covalent radius. 在图 （a） 中，我们正在测量共价半径。
The radius we are measuring in diagram (b) is called the van der Waals radius. This is the only radius that we can determine for neon and argon, because they do not bond with other elements. 我们在图 （b） 中测量的半径称为范德华半径。这是我们唯一可以确定的氖和氩的半径，因为它们不与其他元素键合。
There is a third radius that is used for metals. It is called the metallic radius. 还有第三个半径用于金属。它被称为金属半径。
Fig B shows the trend in covalent radii across the second period (lithium to fluorine, or Li to F) and third period (sodium to chlorine, or Na to Cl)) measured in nanometres (10^(-9)(m))\left(10^{-9} \mathrm{~m}\right). 图 B 显示了第二周期（锂到氟，或锂到氟）和第三周期（钠到氯，或钠到氯，以纳米 )) 为单位）的共价半径趋势 (10^(-9)(m))\left(10^{-9} \mathrm{~m}\right) 。
DID YOU KNOW? 您是否了解？
Different types of radii give different measurements for the same element. The van der Waals radius is always larger. So always compare like with like when you are looking at the trends in atomic radii. 不同类型的半径对同一单元给出不同的测量值。范德华半径总是更大。因此，当您查看原子半径的趋势时，请始终进行同类比较。
fig B Trend in covalent radii across the second and third periods. 图 B 第二和第三周期共价半径的趋势。
You can see that the radius decreases across each period. This is because as the number of protons in the nucleus increases, so does the nuclear charge. This results in an increase in the attractive force between the nucleus and the outer electrons. This increase in attractive force offsets (counterbalances) the increase in electron-electron repulsion as the number of electrons in the outer quantum shell increases. 您可以看到半径在每个周期中都会减小。这是因为随着原子核中质子数量的增加，核电荷也会增加。这导致原子核和外电子之间的吸引力增加。随着外量子壳中电子数量的增加，这种吸引力的增加抵消（抵消了）电子-电子排斥的增加。
MELTING AND BOILING TEMPERATURES 熔化和沸腾温度
Table A below illustrates the changes in melting and boiling temperatures for the elements in Periods 2 and 3. 下面的表 A 说明了周期 2 和 3 中元素的熔化和沸腾温度变化。
PERIOD 2 第 2 期
Li 李
Be 是
B
C (DIAMOND) C （钻石）
N
0\mathbf{0}
F
melting temperature //^(@)C/{ }^{\circ} \mathrm{C} 熔融温度 //^(@)C/{ }^{\circ} \mathrm{C}
181
1278
2300
3550
-210
-218
-220
boiling temperature //^(@)C/{ }^{\circ} \mathrm{C} 沸腾温度 //^(@)C/{ }^{\circ} \mathrm{C}
PERIOD 3 Na Mg Al Si P S CI
melting temperature //^(@)C 98 649 660 1440 44 113 -101
boiling temperature //^(@)C 883 1107 2467 2355 280 445 -35
type of bonding metallic metallic metallic covalent covalent covalent covalent
structure giant lattice giant lattice giant lattice giant lattice "simple
molecular" "simple
molecular" "simple
molecular"| PERIOD 3 | Na | Mg | Al | Si | $\mathbf{P}$ | $\mathbf{S}$ | CI |
| :--- | :---: | :---: | :---: | :---: | :---: | :---: | :---: |
| melting temperature $/{ }^{\circ} \mathrm{C}$ | 98 | 649 | 660 | 1440 | 44 | 113 | -101 |
| boiling temperature $/{ }^{\circ} \mathrm{C}$ | 883 | 1107 | 2467 | 2355 | 280 | 445 | -35 |
| type of bonding | metallic | metallic | metallic | covalent | covalent | covalent | covalent |
| structure | giant lattice | giant lattice | giant lattice | giant lattice | simple <br> molecular | simple <br> molecular | simple <br> molecular |
table A\mathbf{A} Changes in melting and boiling temperatures for Period 2 and 3 elements. 表 A\mathbf{A} 第 2 周期和第 3 周期元素的熔化和沸腾温度变化。
EXAM HINT 考试提示
If you are asked to explain trends in melting points, you do not need to be able to remember specific melting points of elements. You only need to be able to explain the trends in terms of bond type. 如果要求您解释熔点的趋势，您不需要能够记住元素的特定熔点。您只需要能够解释债券类型的趋势。
You may have noticed that the elements with giant lattice structures have high melting and boiling temperatures, and those with simple molecular structures have low melting and boiling temperatures. We will explain the reason for this in Topic 3. 您可能已经注意到，具有巨大晶格结构的元素具有较高的熔化和沸腾温度，而具有简单分子结构的元素具有较低的熔化和沸腾温度。我们将在主题 3 中解释其原因。
FIRST IONISATION ENERGIES 第一电离能
Fig C\mathbf{C} is a plot of first ionisation energy for the first three Periods. 图 C\mathbf{C} 是前三个周期的第一电离能图。 Delta\Delta fig C First ionisation energy for Periods 1-3. Delta\Delta 图 C 第 1-3 周期的第一电离能。
HYDROGEN AND HELIUM 氢气和氦气
The electronic configurations of hydrogen and helium are 1s^(1)1 \mathrm{~s}^{1} and 1s^(2)1 s^{2}, respectively. 氢和氦的电子构型分别为 1s^(1)1 \mathrm{~s}^{1} 和 1s^(2)1 s^{2} 。
We can explain the increase in first ionisation energy from hydrogen to helium by the increase in nuclear charge from 1 to 2 as an extra proton is added. This increase in nuclear charge more than offsets the increase in electron-electron repulsion in the 1 s orbital as a second electron is added. 我们可以解释为什么随着额外质子的增加，核电荷从 1 增加到 2 而从氢到氦的第一电离能增加。随着第二个电子的添加，核电荷的增加超过了 1 s 轨道中电子-电子排斥的增加。
LEARNING TIP 学习小贴士
You may hear or read about a suggestion that the first ionisation energy of boron is less than that of beryllium, because by losing an electron the boron atom will acquire a full 2 s orbital and so become more stable. In fact, because energy has to be supplied to the boron atom in order to remove an electron, the ion formed is energetically less stable than the atom because it has a higher energy value. 您可能听说或读到过这样一种说法，即硼的第一电离能小于铍的第一电离能，因为通过失去一个电子，硼原子将获得完整的 2 s 轨道，从而变得更加稳定。事实上，由于必须向硼原子提供能量才能去除电子，因此形成的离子在能量上不如原子稳定，因为它具有更高的能量值。
ANOMALIES 异常
We have already explained the general increase in first ionisation energy across the period from lithium to neon ( Li to Ne ) and from sodium to argon (Na to Ar), in terms of the increasing nuclear charge. However, you will notice that there are two anomalies in each case. The first ionisation energy of the Group 3 element is less than that of the Group 2 element, and the first ionisation energy of the Group 6 element is less than that of the Group 5 element. 我们已经解释了从锂到氖（Li 到 Ne）和从钠到氩（Na 到 Ar）期间第一电离能的普遍增加，就核电荷的增加而言。但是，您会注意到每种情况下都有两个异常。第 3 族元素的第一电离能小于第 2 族元素的第一电离能，第 6 族元素的第一电离能小于第 5 族元素的第一电离能。
First, consider the case of beryllium (Be) and boron (B). 首先，考虑铍 （Be） 和硼 （B） 的情况。
The electronic configurations are: 电子配置为：
Although the nuclear charge of the boron atom is greater than that of the beryllium atom, the outer electron of boron has more energy, since it is in a 2 p orbital as opposed to the 2 s orbital for beryllium. For this reason, the energy required to remove 2p2 p electron in boron is less than the energy required to remove a 2 s electron from a beryllium atom. In addition, the 2p2 p electron in boron experiences greater electron-electron repulsion (i.e. greater shielding) because there are two inner electron sub-shells as opposed to only one in the beryllium atom. 尽管硼原子的核电荷大于铍原子的核电荷，但硼的外电子具有更多的能量，因为它位于 2 p 轨道上，而铍的轨道为 2 s 轨道。因此，去除 2p2 p 硼中电子所需的能量小于从铍原子中去除 2 s 电子所需的能量。此外，硼中的 2p2 p 电子经历更大的电子-电子排斥（即更大的屏蔽），因为有两个内部电子子壳层，而铍原子中只有一个。
A similar argument applies to magnesium and aluminium (Mg and Al ), except that in this case it involves the 3 s and 3 p electrons. 类似的论点适用于镁和铝（Mg 和 Al），只是在这种情况下它涉及 3 s 和 3 p 电子。
LEARNING TIP 学习小贴士
You may hear or read about an explanation stating that the outer electron in the boron atom is further from the nucleus than the outer electron in the beryllium atom. This is not correct. The boron atom is smaller than the beryllium atom as shown in fig B. 您可能会听到或读到这样一种解释，即硼原子中的外电子比铍原子中的外电子离原子核更远。这是不正确的。硼原子比铍原子小，如图 B 所示。
NITROGEN AND OXYGEN 氮气和氧气
Now consider nitrogen ( N ) and oxygen ( O ). 现在考虑氮 （ N ） 和氧 （ O ）。
The electronic configurations are: 电子配置为：
The first electron removed from the oxygen atom is one of the two paired electrons in the 2p_(x)2 p_{x} orbital. 从氧原子中去除的第一个电子是 2p_(x)2 p_{x} 轨道中两个成对电子之一。
The presence of two electrons in a single orbital increases the electron-electron repulsion in this orbital. So less energy is required to remove one of these electrons than is required to remove a 2 p electron from a nitrogen atom, despite the larger nuclear charge of the oxygen atom. 单个轨道中存在两个电子会增加该轨道中的电子-电子排斥。因此，尽管氧原子的核电荷较大，但去除其中一个电子所需的能量比从氮原子中去除 2 p 电子所需的能量要少。
LEARNING TIP 学习小贴士
You may see an explanation stating that the first ionisation energy of oxygen is less than that of nitrogen, saying this is because when the oxygen atom loses an electron, it acquires a stable half-full 2p2 p subshell. However, there is no special stability associated with a half-full sub-shell. Also, as with the boron atom, energy must be supplied to the oxygen atom in order to remove an electron, so the ion formed is energetically less stable than the atom. 你可能会看到一个解释，说氧的第一电离能小于氮的第一电离能，说这是因为当氧原子失去一个电子时，它会获得一个稳定的半满 2p2 p 亚壳层。但是，半满子壳没有特殊的稳定性。此外，与硼原子一样，必须向氧原子提供能量才能去除电子，因此形成的离子在能量上不如原子稳定。
You may also hear or read about an explanation stating that the outer electron in the oxygen atom is further from the nucleus than the outer electron in the nitrogen atom. This is not correct. The oxygen atom is smaller than the nitrogen atom as shown in fig B. 您可能还会听到或读到一种解释，指出氧原子中的外电子比氮原子中的外电子离原子核更远。这是不正确的。氧原子比氮原子小，如图 B 所示。
CHECKPOINT 检查站
SKILLS REASONING 技能推理
An element has very high melting and boiling temperatures. 元素具有非常高的熔化和沸腾温度。
(a) What type of structure is it likely to have? （a） 它可能具有什么类型的结构？
(b) Which physical property would help you determine whether the bonding was metallic or covalent? Explain your answer. （b） 哪种物理特性可以帮助您确定键合是金属键还是共价键？解释你的答案。
Explain why the first ionisation energy of helium is higher than that of hydrogen. 解释为什么氦的第一电离能高于氢的第一电离能。
Explain why the first ionisation energy of lithium is much lower than that of helium, even though the lithium atom has a greater nuclear charge. 解释为什么锂的第一电离能远低于氦，即使锂原子具有更大的核电荷。
Would you expect the first ionisation energy of gallium (Ga) to be higher or lower than that of calcium (Ca)? Explain your answer. 您预计镓 （Ga） 的第一电离能会高于还是低于钙 （Ca） 的第一电离能？解释你的答案。
Why does neon have the highest first ionisation energy of all the elements in Period 2? 为什么氖在周期 2 的所有元素中具有最高的第一电离能？
SUBJECT VOCABULARY 学科词汇
periodic properties (periodicity) regularly repeating patterns of atomic, physical and chemical properties, which can be predicted using the Periodic Table and explained using the electron configurations of the elements 周期性 （Periodicity） 定期重复原子、物理和化学性质的模式，可以使用元素周期表进行预测，并使用元素的电子构型进行解释
2
THINKING BIGGER 2
放眼更远
ELEMENTAL FINGERPRINTS 元素指纹
Is it possible to know what stars in distant galaxies are made from? 有可能知道遥远星系中的恒星是由什么组成的吗？
ELEMENTAL ‘FINGERPRINTS' 元素“指纹”
In 1825, the French philosopher Auguste Comte said that there are some things we will never know, among these the chemical composition of the stars. This was an unfortunate example. We do not need actual material from the stars in order to analyse them. What we do need, of course, is information, and this they send us plentifully, in the form of light. To reveal this information, we must separate the light into its different wavelengths or colours. 1825 年，法国哲学家奥古斯特·孔德 （Auguste Comte） 说，有些事情我们永远不会知道，其中包括恒星的化学成分。这是一个不幸的例子。我们不需要来自星星的实际材料来分析它们。当然，我们确实需要的是信息，而这些信息以光的形式大量发送给我们。为了揭示这些信息，我们必须将光分成不同的波长或颜色。
Emission spectrum 发射光谱
fig A 图 A
From From Stars to Stalagmites: How Everything Connects by Paul Braterman 从星星到石笋：万物如何连接 保罗·布拉特曼
THINKING BIGGER TIPS 思考更宏大的技巧
An emission spectrum shows the frequencies of electromagnetic radiation that are emitted by a substance. An absorption spectrum shows the frequencies of electromagnetic radiation that are absorbed by the substance. This means that the absorption spectrum is essentially the ‘negative’ of the emission spectrum. 发射光谱显示物质发射的电磁辐射的频率。吸收光谱显示了被物质吸收的电磁辐射的频率。这意味着吸收光谱本质上是发射光谱的“负”值。
Many years earlier Isaac Newton had passed sunlight through a glass prism, and found that this gave him all the colours of the rainbow. In 1802 William Wollaston in England … repeated the experiment, using an up-to-date high quality glass prism, and discovered that the continuous spectrum was interrupted by narrow dark lines. (Rather unfairly these are now known as Frauenhofer lines, after the German physicist Joseph von Frauenhofer, who confirmed and extended Wollaston’s observations). These lines later proved to match exactly the light given out by different elements when heated or in electric discharges. A now familiar example is provided by the element sodium, whose yellow emission is used in street lamps. The lines can be used as a kind of fingerprint for each element. We can take this fingerprint using electrical discharges here on Earth and compare it with the lines found in the spectrum of the Sun. In this way we can get a good chemical analysis of the surface layer of the Sun or of any other star whose light we can collect and astronomers now extend the same process to the most distant galaxies. 许多年前，艾萨克·牛顿 （Isaac Newton） 将阳光穿过玻璃棱镜，发现这给了他彩虹的所有颜色。1802 年，威廉·沃拉斯顿 （William Wollaston） 在英格兰......使用最新的高质量玻璃棱镜重复实验，发现连续光谱被狭窄的黑线打断。（相当不公平的是，这些现在被称为弗劳恩霍夫线，以德国物理学家约瑟夫·冯·弗劳恩霍夫 （Joseph von Frauenhofer） 的名字命名，他证实并扩展了沃拉斯顿的观察结果）。这些线路后来证明与不同元件在加热或放电时发出的光完全匹配。现在熟悉的一个例子是钠元素，其黄色发射用于路灯。这些线条可以用作每个元素的一种指纹。我们可以使用地球上的放电来获取这个指纹，并将其与太阳光谱中发现的线进行比较。通过这种方式，我们可以对太阳或任何其他恒星的表层进行良好的化学分析，天文学家现在将相同的过程扩展到最遥远的星系。
DID YOU KNOW? 您是否了解？
Many images of galaxies taken by the Hubble telescope use the line emission spectra of elements such as hydrogen, sulfur and oxygen to build up a colour image of the galaxy. The different elements are assigned red, green and blue frequencies to build up a full colour image. 哈勃望远镜拍摄的许多星系图像都使用氢、硫和氧等元素的线发射光谱来构建星系的彩色图像。不同的元素被分配了红色、绿色和蓝色频率，以构建全彩色图像。
SCIENGE COMMUNIGATION 科学通讯
The extract is taken from the book From Stars to Stalagmites: How Everything Connects by Paul Braterman (2012). 摘录自保罗·布拉特曼 （Paul Braterman） （2012） 的《从星星到石笋：万物如何连接》一书。
(a) Do you think this article is aimed at scientists, the general public, or people who are not scientists but have an interest in science? Look back through the extract and find examples to support your answer. （a） 你认为这篇文章是针对科学家、公众还是不是科学家但对科学感兴趣的人？回顾摘录并找到示例来支持您的答案。
(b) Explain how the book’s subtitle How Everything Connects is supported by the extract. （b） 解释该摘录如何支持该书的副标题“万物如何连接”。
Would you expect heavier isotopes of sodium to give a different ‘fingerprint’? Explain your answer. 您会期望较重的钠同位素产生不同的“指纹”吗？解释你的答案。
The element helium was first discovered in the outer layer of the Sun. Suggest why it was discovered there before it was discovered here on Earth. Think back to work you have done on identifying alkali metals using flame tests. 氦元素最早是在太阳的外层发现的。请说明为什么它在地球上被发现之前就在那里被发现。回想一下您使用火焰测试识别碱金属所做的工作。
ACTIVITY 活动
Today, the elemental fingerprints in the light collected from distant galaxies have provided evidence for an expanding universe. The elemental fingerprints are subject to a phenomenon called ‘red shift’. 今天，从遥远星系收集的光中的元素指纹为宇宙膨胀提供了证据。元素指纹会受到一种称为“红移”的现象的影响。
Explain in 200-300 words how red shift has provided evidence for an expanding universe. Try to structure your explanation so that the concepts can be understood by an audience of 16 -year-old students. 用 200-300 字解释红移如何为膨胀的宇宙提供证据。尝试构建您的解释，以便 16 岁的学生可以理解这些概念。
fig B A picture taken by the Hubble Telescope showing over 10000 galaxies! 图 B 哈勃望远镜拍摄的照片显示了超过 10000 个星系！
THINKING BIGGER TIP 考虑更宏大的建议
As well as considering the complexity of the scientific ideas, think about the level of detail in which they are discussed. Notice how many different branches of natural science are mentioned in the extract. Are all of the scientists mentioned chemists or did they work in different scientific disciplines? 除了考虑科学思想的复杂性外，还要考虑讨论它们的细节程度。请注意摘录中提到了多少个不同的自然科学分支。是所有科学家都提到了化学家，还是他们在不同的科学学科工作？
WRITING SCIENTIFICALLY 科学写作
You need to use reasoning and maybe examples to give an explanation of your answer and support your point. Consider how the particles involved (e.g. atoms, ions, molecules, electrons, etc.) affect your answer. 你需要使用推理，也许还有例子来解释你的答案并支持你的观点。考虑所涉及的粒子（例如原子、离子、分子、电子等）如何影响您的答案。
THINKING BIGGER TIP 考虑更宏大的建议
The Activity provides opportunity for creative explanation of advanced concept to younger students. 该活动为低年级学生提供了创造性地解释高级概念的机会。
1 The relative atomic mass of boron is 10.8 . 1 硼的相对原子质量为 10.8 。
A sample of boron contains the isotopes _(5)^(10)B{ }_{5}^{10} \mathrm{~B} and _(5)^(11)B{ }_{5}^{11} \mathrm{~B}. 硼样品包含同位素 _(5)^(10)B{ }_{5}^{10} \mathrm{~B} 和 _(5)^(11)B{ }_{5}^{11} \mathrm{~B} 。
What is the percentage of _(5)^(11)B{ }_{5}^{11} \mathrm{~B} atoms in the isotopic mixture of this sample? 该样品的同位素混合物中 _(5)^(11)B{ }_{5}^{11} \mathrm{~B} 原子的百分比是多少？
A 0.8%0.8 \% 一个 0.8%0.8 \%
B 8.0%8.0 \% 乙 8.0%8.0 \%
C 20%20 \% 丙 20%20 \%
D 80%80 \%
[1]
(Total for Question 1 = 1 mark) （问题 1 的总分 = 1 分）
2 Which of the following elements has no paired pp electrons in a single uncombined atom of the element? 2 以下哪种元素在该元素的单个未组合原子中没有成对 pp 电子？
A carbon 碳
B oxygen B 氧
C fluorine D neon C 氟 D 霓虹灯
[1]
(Total for Question 2=12=1 mark) （问 2=12=1 号总计）
3. Which of the following electronic configurations is that of an atom of an element which forms a simple ion with a charge of -3 ? 3. 以下哪种电子构型是形成电荷为 -3 的简单离子的元素的原子构型？
A 1s^(2)2s^(2)2p^(6)3s^(2)3p^(1)1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{1} 一个 1s^(2)2s^(2)2p^(6)3s^(2)3p^(1)1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{1}
B 1s^(2)2s^(2)2p^(6)3s^(2)3p^(3)1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{3} 乙 1s^(2)2s^(2)2p^(6)3s^(2)3p^(3)1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{3}
C 1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)3d^(1)4s^(2)1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{6} 3 d^{1} 4 s^{2} 丙 1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)3d^(1)4s^(2)1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{6} 3 d^{1} 4 s^{2}
D 1s^(2)2s^(2)2p^(6)3s^(2)3p^(6)3d^(3)4s^(2)1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p^{6} 3 d^{3} 4 s^{2}
(Total for Question 3=13=1 mark) （问 3=13=1 号总计）
4 A sample of chlorine contains isotopes of mass numbers 35 and 37. 4 氯样品含有质量数为 35 和 37 的同位素。
The sample is analysed in a mass spectrometer. How many peaks corresponding to Cl_(2)^(+)\mathrm{Cl}_{2}{ }^{+}are recorded? 样品在质谱仪中进行分析。记录了多少个对应的 Cl_(2)^(+)\mathrm{Cl}_{2}{ }^{+} 峰？
A 1 答 1
B 2 乙 2
C 3
D 4
(Total for Question 4=14=1 mark) （问 4=14=1 号总计）
Symbol of
element| Symbol of |
| :--- |
| element |
Na\mathbf{N a}
Mg\mathbf{M g}
Al\mathbf{A l}
Si\mathbf{S i}
P\mathbf{P}
S\mathbf{S}
Cl\mathbf{C l}
熔融温度 //^(@)C/{ }^{\circ} \mathrm{C}
melting
temperature //^(@)C/{ }^{\circ} \mathrm{C}
melting
temperature //^(@)C| melting |
| :--- |
| temperature $/{ }^{\circ} \mathrm{C}$ |
98
649
660
1410
44
113
-101
bonding 粘 接
structure 结构
"Symbol of
element" Na Mg Al Si P S Cl
"melting
temperature //^(@)C" 98 649 660 1410 44 113 -101
bonding
structure | Symbol of <br> element | $\mathbf{N a}$ | $\mathbf{M g}$ | $\mathbf{A l}$ | $\mathbf{S i}$ | $\mathbf{P}$ | $\mathbf{S}$ | $\mathbf{C l}$ |
| :--- | :---: | :---: | :---: | :---: | :---: | :---: | :---: |
| melting <br> temperature $/{ }^{\circ} \mathrm{C}$ | 98 | 649 | 660 | 1410 | 44 | 113 | -101 |
| bonding | | | | | | | |
| structure | | | | | | | |
Complete the table using the following guidelines. 使用以下准则完成表。
(i) Complete the ‘bonding’ row using only the words ‘metallic’ or ‘covalent’. （i） 仅使用“金属”或“共价”一词填写“键合”行。
(ii) Complete the ‘structure’ row using only the words ‘simple molecular’ or ‘giant lattice’. （ii） 仅使用“简单分子”或“巨晶格”一词填写“结构”行。
(iii) Explain why the melting temperature of phosphorus is different from that of silicon. （iii） 解释为什么磷的熔化温度与硅的熔化温度不同。
10 (a) Complete the table to show the properties of the three major sub-atomic particles. 10 （a） 完成表格以显示三个主要亚原子粒子的性质。
Particle 粒子
Relative charge 相对电荷
Relative mass 相对质量
proton 质子
neutron 中子
electron 电子
Particle Relative charge Relative mass
proton
neutron
electron | Particle | Relative charge | Relative mass |
| :--- | :--- | :--- |
| proton | | |
| neutron | | |
| electron | | |
12 Chlorine has two isotopes, ^(35)Cl{ }^{35} \mathrm{Cl} and ^(37)Cl{ }^{37} \mathrm{Cl}. 12 氯有两种同位素， ^(35)Cl{ }^{35} \mathrm{Cl} 和 ^(37)Cl{ }^{37} \mathrm{Cl} 。
The diagram shows part of the mass spectrum of a sample of chlorine gas. 该图显示了氯气样品的部分质谱图。
(a) Give the formula of the species responsible for each peak at m//zm / z of 70,72 and 74 . （a） 给出负责 70,72 和 74 处 m//zm / z 每个峰值的物种的公式。
(b) Give the m//zm / z ratio for the two other peaks in the mass spectrum of chlorine. Give the formula of the species responsible for each peak and state the relative abundance of these two species. （b） 给出氯质谱中其他两个峰的 m//zm / z 比率。给出负责每个峰的物种的公式，并说明这两个物种的相对丰度。
13 The table gives the first four ionisation energies of the elements sodium, magnesium and aluminium. 13 该表给出了钠、镁和铝元素的前四种电离能。
A IONIC BONDING I B COVALENT BONDING IC SHAPES OF MOLECULES ID METALLIC BONDING IE SOLID LATTICES A 离子键 I B 共价键 IC 分子的形状 ID 金属键 IE 固体晶格
Now that we know something of the structure of atoms, in particular their electronic configurations, we can look at how atoms combine. Knowing about the way substances are bonded, and the effect that the bonding and structure has on chemical and physical properties, is essential to the development of new materials. These new materials are then used to refine and improve products. Computers and mobile phones are smaller, lighter and faster than ever before. New and better materials for clothes and shoes, particularly for use outdoors in bad weather conditions, are constantly being developed. Polymers and composites have almost completely taken the place of more traditional materials such as wood and metal for many uses. 现在我们对原子的结构有所了解，特别是它们的电子构型，我们可以看看原子是如何结合的。了解物质的键合方式以及键合和结构对化学和物理特性的影响，对于新材料的开发至关重要。然后使用这些新材料来改进和改进产品。计算机和移动电话比以往任何时候都更小、更轻、更快。人们不断开发新的和更好的衣服和鞋子材料，特别是在恶劣天气条件下的户外使用。聚合物和复合材料在许多用途中几乎完全取代了木材和金属等更传统的材料。
Knowledge of the shapes of molecules is of fundamental importance in understanding how medicines work and for the future design of new medicines. Knowing the shapes of enzymes is important in the development of biochemical catalysts for chemical reactions. The shapes of macromolecules such as DNA and proteins are extremely complicated. However, the rules that govern their shapes are the same as the rules used to predict the shapes of simple molecules such as methane, water and ammonia. 了解分子的形状对于了解药物的工作原理和未来新药的设计至关重要。了解酶的形状对于开发用于化学反应的生化催化剂非常重要。DNA 和蛋白质等大分子的形状极其复杂。然而，控制其形状的规则与用于预测简单分子（如甲烷、水和氨）形状的规则相同。
MATHS SKILLS FOR THIS TOPIC 本主题的数学技能
Use angles and shapes in regular 2D and 3D structures 在常规 2D 和 3D 结构中使用角度和形状
Visualise and represent 2D and 3D forms including two-dimensional representations of 3D objects 可视化和表示 2D 和 3D 形式，包括 3D 对象的二维表示
Understand the symmetry of 2D and 3D shapes 了解 2D 和 3D 形状的对称性
What will I study in this topic? 我将在本主题中学习什么？
The nature of metallic, ionic, covalent, polar covalent and dative covalent bonding The nature of intermolecular interactions, including hydrogen bonding 金属、离子、共价、极性共价键和配位共价键的性质分子间相互作用的性质，包括氢键
The shapes of discrete (simple) molecules 离散（简单）分子的形状
Electronegativity and polarity of molecules 分子的电负性和极性
An explanation of the physical properties of substances based on their bonding and structure 根据物质的键合和结构对物质的物理性质进行解释
LEARNING OBJECTIVES 学习目标
Describe the formation of ions in terms of loss or gain of electrons. 根据电子的损耗或增益来描述离子的形成。
Draw dot-and-cross diagrams to show electrons in cations and anions. 绘制点交叉图以显示阳离子和阴离子中的电子。
Know that ionic bonding is the result of strong net electrostatic attraction between oppositely charged ions. 要知道，离子键是带相反电荷的离子之间强烈的净静电吸引的结果。
Know and be able to interpret evidence for the existence of ions using electron density maps and from the migrations of ions. 了解并能够使用电子密度图和离子迁移来解释离子存在的证据。
THE FORMATION OF CATIONS AND ANIONS 阳离子和阴离子的形成
Some ionic compounds can be formed by the direct combination of two elements. 一些离子化合物可以通过两种元素的直接结合形成。
FORMATION OF SODIUM AND CHLORIDE IONS 钠离子和氯离子的形成
For example, sodium chloride can be formed by burning sodium in chlorine: 例如，可以通过在氯中燃烧钠来生成氯化钠：
Each sodium atom has lost one electron to become a positive sodium ion. The chlorine molecule has gained two electrons to become two chloride ions. 每个钠原子都失去了一个电子，成为正钠离子。氯分子获得了两个电子，变成了两个氯离子。
We can represent the electronic changes involved by dot-andcross diagrams. 我们可以用点交叉图来表示所涉及的电子变化。
A fig A Dot-and-cross diagram showing the formation of sodium and chloride ions. 图 A 显示钠离子和氯离子形成的点十字图。
LEARNING TIP 学习小贴士
It is important when drawing a dot-and-cross diagram to represent the electrons of one atom using a cross and the other using a dot. You only need to show the outer electrons. 在绘制点交叉图时，用十字表示一个原子的电子，用点表示另一个原子的电子，这一点很重要。你只需要显示外部电子。
FORMATION OF MAGNESIUM AND OXIDE IONS 镁离子和氧离子的形成
Here is the equation for the formation of magnesium oxide: 以下是氧化镁形成的方程式：
A dot-and-cross diagram for the reaction between magnesium and oxygen is shown in fig B. 镁和氧之间反应的点十字图如图 B 所示。
A fig B Dot-and-cross diagram showing the formation of magnesium and oxide ions. 图 B 显示镁离子和氧离子形成的点十字图。
THE NATURE OF IONIC BONDING 离子键的本质
Ionic bonding occurs in solid materials consisting of a regular array of oppositely charged ions extending throughout a giant lattice network. 离子键发生在固体材料中，该材料由规则的带相反电荷的离子阵列组成，这些离子在整个巨大的晶格网络中延伸。
The most familiar ionic compound is sodium chloride, NaCl . It consists of a regular array of sodium ions, Na^(+)\mathrm{Na}^{+}, and chloride ions, Cl^(-)\mathrm{Cl}^{-}, as shown in fig C . 最熟悉的离子化合物是氯化钠 NaCl .它由一系列规则的钠离子 Na^(+)\mathrm{Na}^{+} 和氯离子组成， Cl^(-)\mathrm{Cl}^{-} 如图 C 所示。 /_\\triangle fig C Structure of sodium chloride. /_\\triangle 图 C 氯化钠的结构。
The diagram on the left is an ‘exploded’ version of the structure, which is often drawn for the sake of clarity. In practice, the ions are touching one another, as shown in the diagram on the right. 左边的图表是结构的“分解”版本，通常是为了清晰起见而绘制的。在实践中，离子会相互接触，如右图所示。
EXAM HINT 考试提示
It is worth practising drawing a section of an ionic crystal as you may be asked to do so in an exam. Remember to include a key to show which ion is which. 练习绘制离子晶体的一部分是值得的，因为您可能会在考试中被要求这样做。请记住包含一个键来显示哪个离子是哪个离子。
In an ionic solid, there are strong electrostatic interactions between the ions. The ions are arranged in such a way that the electrostatic 在离子固体中，离子之间存在很强的静电相互作用。离子的排列方式使静电
attractions between the oppositely charged ions are greater than the electrostatic repulsions between ions with the same charge. The electrostatic interaction between ions is not directional: all that matters is the distance between two ions, not their orientation with respect to one another. (Compare this with covalent bonding in Topic 3B.) 带相反电荷的离子之间的吸引力大于具有相同电荷的离子之间的静电排斥。离子之间的静电相互作用不是方向性的：重要的是两个离子之间的距离，而不是它们彼此之间的方向。（将此与主题 3B 中的共价键进行比较。
When ions are present, the electrostatic interaction between them tends to be dominant. However, it is possible for there to be significant covalent interactions between ions, so you should think of pure ionic bonding as an idealised bonding situation. We will develop this concept further in Topic 12B (Book 2: IAL). 当存在离子时，它们之间的静电相互作用往往占主导地位。然而，离子之间可能存在显着的共价相互作用，因此您应该将纯离子键视为一种理想的键合情况。我们将在主题 12B（第 2 册：IAL）中进一步发展这个概念。
THE STRENGTH OF IONIC BONDING 离子键合的强度
You can determine the strength of ionic bonding by calculating the amount of energy required in one mole of solid to separate the ions to infinity (i.e. in the gas phase). When they are at an infinite distance from one another, the ions can no longer interact. 您可以通过计算一摩尔固体中将离子分离到无穷大（即在气相中）所需的能量来确定离子键的强度。当它们彼此相距无限远时，离子就不能再相互作用。
Table A below shows the energy required to separate to infinity the ions in one mole of various alkali metal halides. 下面的表 A 显示了将一摩尔各种碱金属卤化物中的离子分离到无穷大所需的能量。
AMOUNT OF ENERGY REQURED TO SEPARATE THE IONS TO INFINITY / kJmol^(-1)\mathrm{kJ} \mathrm{mol}^{-1} 将离子分离到无穷大所需的能量 / kJmol^(-1)\mathrm{kJ} \mathrm{mol}^{-1}
table A\mathbf{A} Energy required to break up a lattice of an ionic compound. 表 A\mathbf{A} 分解离子化合物晶格所需的能量。
For ions of the same charge, the smaller the ions the more energy is required to overcome the electrostatic interactions between the ions and to separate them. 对于相同电荷的离子，离子越小，克服离子之间的静电相互作用并分离它们所需的能量就越多。
The size of the ions is one factor that affects the strength of ionic bonding, which in turn determines how closely packed the ions are in the lattice. 离子的大小是影响离子键强度的一个因素，而离子键合强度又决定了离子在晶格中的堆积程度。
The lattice energy for lithium fluoride, Li^(+)F^(-)\mathrm{Li}^{+} \mathrm{F}^{-}, is 1031kJmol^(-1)1031 \mathrm{~kJ} \mathrm{~mol}^{-1}. The equivalent energy for magnesium fluoride, Mg^(2+)(F^(-))_(2)\mathrm{Mg}^{2+}\left(\mathrm{F}^{-}\right)_{2}, is 2957kJmol^(-1)2957 \mathrm{~kJ} \mathrm{~mol}^{-1}. The radius of the Mg^(2+)\mathrm{Mg}^{2+} ion (0.072nm)(0.072 \mathrm{~nm}) is very similar to the radius of the Li^(+)\mathrm{Li}^{+}ion (0.074nm)(0.074 \mathrm{~nm}). The increased charge of the Mg^(2+)\mathrm{Mg}^{2+} ion compared to the Li^(+)\mathrm{Li}^{+}ion results in a significant increase in the strength of the ionic bonding. 氟化锂的晶格能量 Li^(+)F^(-)\mathrm{Li}^{+} \mathrm{F}^{-} 为 1031kJmol^(-1)1031 \mathrm{~kJ} \mathrm{~mol}^{-1} 。氟化镁的等效能量 Mg^(2+)(F^(-))_(2)\mathrm{Mg}^{2+}\left(\mathrm{F}^{-}\right)_{2} 为 2957kJmol^(-1)2957 \mathrm{~kJ} \mathrm{~mol}^{-1} 。 Mg^(2+)\mathrm{Mg}^{2+} 离子 (0.072nm)(0.072 \mathrm{~nm}) 的半径与 Li^(+)\mathrm{Li}^{+} 离子 (0.074nm)(0.074 \mathrm{~nm}) 的半径非常相似。与离子相比， Mg^(2+)\mathrm{Mg}^{2+}Li^(+)\mathrm{Li}^{+} 离子电荷的增加导致离子键合强度的显着增加。
When both cation and anion are doubly charged, the energy required to separate the ions is even larger. For magnesium oxide, Mg^(2+)O^(2-)\mathrm{Mg}^{2+} \mathrm{O}^{2-}, the value is 3791kJmol^(-1)3791 \mathrm{~kJ} \mathrm{~mol}^{-1}. 当阳离子和阴离子都带双电荷时，分离离子所需的能量甚至更大。对于氧化镁， Mg^(2+)O^(2-)\mathrm{Mg}^{2+} \mathrm{O}^{2-} ，值为 3791kJmol^(-1)3791 \mathrm{~kJ} \mathrm{~mol}^{-1} 。
There is no simple mathematical relationship to describe the effects that ionic radius and ionic charge have on the strength of ionic bonding. The situation is complicated by the way in which the ions pack together to form the lattice, and by the extent to which there are covalent interactions between the ions. In general, however, the smaller the ions and the larger the charge on the ions, the stronger the ionic bonding. 没有简单的数学关系来描述离子半径和离子电荷对离子键强度的影响。由于离子堆积在一起形成晶格的方式以及离子之间存在共价相互作用的程度，情况变得复杂。然而，一般来说，离子越小，离子上的电荷越大，离子键合就越强。
EVIDENCE FOR THE EXISTENCE OF IONS 离子存在的证据
Ionic compounds can conduct electricity and undergo electrolysis when either molten or in aqueous solution. This is the most convincing evidence for the existence of ions. 离子化合物在熔融或水溶液中可以导电并发生电解。这是离子存在的最有说服力的证据。
For example, when you pass a direct electric current through molten sodium chloride (fig D), sodium is formed at the negative electrode and chlorine is formed at the positive electrode. 例如，当您将直流电通过熔融氯化钠（图 D）时，在负极形成钠，在正极形成氯。 Delta\Delta
fig D Electrolysis of molten sodium chloride. 图 D 熔融氯化钠的电解。
LEARNING TIP 学习小贴士
Avoid saying that there is an ‘ionic bond’ between two ions. 避免说两个离子之间存在“离子键”。
This is because in an ionic solid, each ion interacts with many other ions, of both the same and opposite charge to itself. The energy that binds the structure does not come from single interactions between ions (so-called ionic bonds), but from the interactions between all of the ions in the lattice. This energy is called the ‘lattice energy’ and you will meet this in Topic 12B (Book 2: IAL). 这是因为在离子固体中，每个离子都与许多其他离子相互作用，这些离子与自身电荷相同或相反。结合结构的能量不是来自离子之间的单一相互作用（所谓的离子键），而是来自晶格中所有离子之间的相互作用。这种能量被称为“晶格能量”，您将在主题 12B（第 2 册：IAL）中遇到它。 Delta\Delta fig E\mathbf{E} The effect of passing an electric current through aqueous copper(II) chromate. Delta\Delta 图 E\mathbf{E} 电流通过铬酸铜 （II） 水溶液的效果。
SKILLS REASONING 技能推理
The explanation for this phenomenon is that: 对这种现象的解释是：
the positive sodium ions migrate towards the negative electrode where they gain electrons and become sodium atoms 正钠离子向负极迁移，在那里它们获得电子并成为钠原子
the negative chloride ions migrate towards the positive electrode where they lose electrons and become chlorine molecules. 负氯离子向正极迁移，在那里它们失去电子并变成氯分子。
At the negative electrode: 2Na^(+)+2e^(-)rarr2Na2 \mathrm{Na}^{+}+2 \mathrm{e}^{-} \rightarrow 2 \mathrm{Na} 在负极处： 2Na^(+)+2e^(-)rarr2Na2 \mathrm{Na}^{+}+2 \mathrm{e}^{-} \rightarrow 2 \mathrm{Na}
At the positive electrode: quad2Cl^(-)rarrCl_(2)+2e^(-)\quad 2 \mathrm{Cl}^{-} \rightarrow \mathrm{Cl}_{2}+2 \mathrm{e}^{-} 在正极处： quad2Cl^(-)rarrCl_(2)+2e^(-)\quad 2 \mathrm{Cl}^{-} \rightarrow \mathrm{Cl}_{2}+2 \mathrm{e}^{-}
Overall equation: quad2NaClrarr2Na+Cl_(2)\quad 2 \mathrm{NaCl} \rightarrow 2 \mathrm{Na}+\mathrm{Cl}_{2} 总体方程式： quad2NaClrarr2Na+Cl_(2)\quad 2 \mathrm{NaCl} \rightarrow 2 \mathrm{Na}+\mathrm{Cl}_{2}
We can demonstrate the movement of ions by passing a direct current through copper(II) chromate(VI) solution (fig E). Aqueous copper(II) ions, Cu^(2+)(aq)\mathrm{Cu}^{2+}(\mathrm{aq}), are blue and aqueous chromate(VI) ions, CrO_(4)^(2-)(aq)\mathrm{CrO}_{4}^{2-}(\mathrm{aq}), are yellow. 我们可以通过使直流电通过铜 （II） 铬酸盐 （VI） 溶液来证明离子的运动（图 E）。铜 （II） 水离子 Cu^(2+)(aq)\mathrm{Cu}^{2+}(\mathrm{aq}) ， 为蓝色，铬酸盐 （VI） 水离子 CrO_(4)^(2-)(aq)\mathrm{CrO}_{4}^{2-}(\mathrm{aq}) 为 黄色。
The Cu^(2+)(aq)\mathrm{Cu}^{2+}(\mathrm{aq}) ions migrate towards the negative electrode and the solution around this electrode turns blue. The CrO_(4)^(2-)(aq)\mathrm{CrO}_{4}^{2-}(\mathrm{aq}) ions migrate towards the positive terminal and the solution around this electrode turns yellow. Cu^(2+)(aq)\mathrm{Cu}^{2+}(\mathrm{aq}) 离子向负极迁移，该电极周围的溶液变为蓝色。 CrO_(4)^(2-)(aq)\mathrm{CrO}_{4}^{2-}(\mathrm{aq}) 离子向正极迁移，该电极周围的溶液变为黄色。
Further evidence for the existence of ions is supplied by electron density maps. 电子密度图提供了离子存在的进一步证据。
Fig F\mathbf{F} is an electron density map for sodium chloride. 图 F\mathbf{F} 是氯化钠的电子密度图。
A
A
fig F Electron density map of sodium chloride produced from X-ray diffraction patterns. 图 F 由 X 射线衍射图谱产生的氯化钠的电子密度图。
The electron density map clearly shows separate ions. A represents a sodium ion and B represents a chloride ion. 电子密度图清楚地显示了单独的离子。A 代表钠离子，B 代表氯离子。
CHECKPOINT 检查站
Explain what is meant by the term ‘ionic bonding’. 解释术语“离子键”的含义。
Calcium reacts with fluorine to form the ionic compound calcium fluoride: 钙与氟反应形成离子化合物氟化钙：
Use a dot-and-cross diagram to show the electronic changes that occur in this reaction. 使用点十字图显示该反应中发生的电子变化。
3. (a) Suggest why the strength of ionic bonding is greater in sodium fluoride than in potassium fluoride. 3. （a） 说明为什么氟化钠的离子键强度大于氟化钾。
(b) Suggest why the strength of ionic bonding in calcium oxide is approximately four times larger than that in potassium fluoride. （b） 说明为什么氧化钙中的离子键强度大约是氟化钾中的四倍。
SUBJECT VOCABULARY 学科词汇
ionic bonding the electrostatic attraction between oppositely charged ions 离子键合 带相反电荷的离子之间的静电吸引
3A3 A
2 IONIC RADII AND POLARISATION OF IONS 3A3 A 2 离子半径和离子极化
LEARNING OBJECTIVES 学习目标
Understand the effects of ionic radius and ionic charge on the strength of ionic bonding. 了解离子半径和离子电荷对离子键强度的影响。
Understand reasons for the trends in ionic radii down a group in the Periodic Table, and for a set of isoelectronic ions, e.g. N^(3-)\mathrm{N}^{3-} to Al^(3+)\mathrm{Al}^{3+}. 了解元素周期表中一组离子半径下降趋势以及一组等电子离子（例如 N^(3-)\mathrm{N}^{3-} 到 Al^(3+)\mathrm{Al}^{3+} ）的原因。
Understand the meaning of the term polarisation as applied to ions. 了解术语极化应用于离子的含义。
TRENDS IN IONIC RADII 离子半径的趋势
Ionic radii are difficult to measure accurately, and vary according to the environment of the ion. For example, it is important how many oppositely charged ions are touching it (i.e. the co-ordination number). The nature of the ions is also important. 离子半径难以准确测量，并且根据离子环境而变化。例如，有多少带相反电荷的离子接触到它（即配位数）很重要。离子的性质也很重要。
There are several different ways of measuring ionic radii and they all produce slightly different values. If you are going to make reliable comparisons using ionic radii, all the values must come from the same source. 有几种不同的方法来测量离子半径，它们产生的值都略有不同。如果要使用离子半径进行可靠的比较，则所有值必须来自同一来源。
Remember that there are quite large uncertainties when using ionic radii. Trying to explain things in detail is made difficult because of those uncertainties. 请记住，使用离子半径时存在相当大的不确定性。由于这些不确定性，试图详细解释事情变得困难。
table A Trends in ionic radii in Groups 1 and 7. 表 A 第 1 组和第 7 组离子半径的趋势。
As you go down each group, the ions have more electron shells; therefore, the ions get larger. 随着你沿着每组向下走，离子有更多的电子壳层;因此，离子变得更大。
table B Trends in ionic radii across a period. 表 B 一段时间内离子半径的趋势。
All six of the ions listed in table B are isoelectronic. In other words, they have the same number of electrons and therefore the same electronic configuration. 表 B 中列出的所有 6 个离子都是等电子离子。换句话说，它们具有相同的电子数量，因此具有相同的电子配置。
The ionic radius decreases as the number of protons increases. 离子半径随着质子数量的增加而减小。
As the positive charge of the nucleus increases, the electrons are attracted more strongly and are therefore pulled closer to the nucleus. 随着原子核的正电荷增加，电子被更强烈地吸引，因此被拉得更靠近原子核。
POLARISATION AND POLARISING POWER OF IONS 离子的极化和极化能力
In an ionic lattice, the positive ion will attract the electrons of the anion. If the electrons are pulled towards the cation, the anion is polarised since the even distribution of its electron density has been distorted. 在离子晶格中，正离子会吸引阴离子的电子。如果电子被拉向阳离子，阴离子就会极化，因为其电子密度的均匀分布已经扭曲。
The extent to which an anion is polarised by a cation depends on several factors. The two main factors are known as Fajan’s rules and are summarised here. 阴离子被阳离子极化的程度取决于几个因素。这两个主要因素被称为 Fajan 规则，总结如下。
DID YOU KNOW? 您是否了解？
When you compare chemical values, you should make sure all the data you are comparing come from the same source. For example, the values in tables B and C\mathbf{C} have all been taken from the Database of Ionic Radii from Imperial College London. However, Chemistry Data Book (JG Stark and HG Wallace) gives a value of 0.171 for the ionic radius of the nitride ion, N^(3-)\mathrm{N}^{3-}. In either case, the value is larger than that for the oxide ion, 0^(2-)0^{2-}, as expected. 当您比较化学值时，您应该确保您正在比较的所有数据都来自同一来源。例如，表 B 和 C\mathbf{C} 中的值均取自伦敦帝国理工学院的 Database of Ionic Radii。然而，化学数据手册（JG Stark 和 HG Wallace）给出的氮化物离子 N^(3-)\mathrm{N}^{3-} 半径值为 0.171。无论哪种情况，该值都大于氧化物离子 的值， 0^(2-)0^{2-} 正如预期的那样。
Region where electrons are existing in an area of orbital overlap 电子存在于轨道重叠区域中的区域 Deltaquad\Delta \quad fig A A representation of a cation attracting the electrons of an anion in an ionic lattice. Deltaquad\Delta \quad 图 A 在离子晶格中吸引阴离子电子的阳离子的表示。
Polarisation will be increased by: 两极分化将通过以下方式增加：
high charge and small size of the cation (i.e. high charge density of the cation) 阳离子电荷高且尺寸小（即阳离子的电荷密度高）
high charge and large size of the anion. 高电荷和大阴离子尺寸。
HIGH CHARGE AND SMALL SIZE OF CATIONS 高电荷和小尺寸阳离子
The ability of a cation to attract electrons from the anion towards itself is called its polarising power. A cation with a high charge and a small radius has a large polarising power. An approximate value for the polarising power of a cation can be obtained by calculating its charge density. The charge density of a cation is the charge divided by the surface area of the ion. If the ion is assumed to be a sphere, its surface area is equal to 4pir^(2)4 \pi r^{2}, where rr is the ionic radius. 阳离子将电子从阴离子吸引到自身的能力称为其极化能力。电荷大、半径小的阳离子具有较大的极化能力。阳离子的极化能力的近似值可以通过计算其电荷密度来获得。阳离子的电荷密度是电荷除以离子的表面积。如果假设离子是一个球体，则其表面积等于 4pir^(2)4 \pi r^{2} ，其中 rr 是离子半径。
An approximation to the charge density can be determined by dividing the charge by the square of its ionic radius. 电荷密度的近似值可以通过将电荷除以其离子半径的平方来确定。
" charge density "∼(" charge ")/(r^(2))\text { charge density } \sim \frac{\text { charge }}{\mathrm{r}^{2}}
HIGH CHARGE AND LARGE SIZE OF ANIONS 高电荷和大尺寸阴离子
The ease with which an anion is polarised depends on its charge and its size. Anions with a high charge and a large size are polarised the most easily. 阴离子极化的难易程度取决于其电荷和大小。高电荷和大尺寸的阴离子最容易极化。
In an ionic lattice, the polarisation of the anions creates some degree of sharing of electrons between the two nuclei. That is, some degree of covalent bonding exists. You will learn more about this concept in Topic 12B (Book 2: IAL). 在离子晶格中，阴离子的极化在两个原子核之间产生了一定程度的电子共享。也就是说，存在一定程度的共价键。您将在主题 12B（第 2 册：IAL）中了解有关此概念的更多信息。
CHECKPOINT 检查站
Explain the trend in the following ionic radii: 解释以下离子半径的趋势：
(a) Ca^(2+) > Mg^(2+) > Be^(2+)\mathrm{Ca}^{2+}>\mathrm{Mg}^{2+}>\mathrm{Be}^{2+} （一） Ca^(2+) > Mg^(2+) > Be^(2+)\mathrm{Ca}^{2+}>\mathrm{Mg}^{2+}>\mathrm{Be}^{2+}
(b) P^(3-) > S^(2-) > Cl^(-)\mathrm{P}^{3-}>\mathrm{S}^{2-}>\mathrm{Cl}^{-} （二） P^(3-) > S^(2-) > Cl^(-)\mathrm{P}^{3-}>\mathrm{S}^{2-}>\mathrm{Cl}^{-}
The table gives the ionic radii of some ions. 该表给出了一些离子的离子半径。
FORMULA OF ION 离子的公式
IONIC RADIUS / nm 离子半径 / nm
Li^(+)\mathrm{Li}^{+}
0.076
Na^(+)\mathrm{Na}^{+}
0.102
Mg^(2+)\mathrm{Mg}^{2+}
0.072
Al^(3+)\mathrm{Al}^{3+}
0.054
FORMULA OF ION IONIC RADIUS / nm
Li^(+) 0.076
Na^(+) 0.102
Mg^(2+) 0.072
Al^(3+) 0.054| FORMULA OF ION | IONIC RADIUS / nm |
| :---: | :---: |
| $\mathrm{Li}^{+}$ | 0.076 |
| $\mathrm{Na}^{+}$ | 0.102 |
| $\mathrm{Mg}^{2+}$ | 0.072 |
| $\mathrm{Al}^{3+}$ | 0.054 |
Arrange the ions in order of their polarising power. Show how you arrived at your answer. 按离子的极化能力顺序排列离子。展示您是如何得出答案的。
SUBJECT VOCABULARY 学科词汇
polarising power the ability of a positive ion (cation) to distort the electron density of a neighbouring negative ion (anion) 极化能力 正离子（阳离子）扭曲相邻负离子（阴离子）的电子密度的能力
polarisation the distortion of the electron density of a negative ion (anion) 极化：负离子（阴离子）电子密度的扭曲
3A3 A 3 PHYSICAL PROPERTIES OF IONIC COMPOUNDS 3A3 A 3 离子化合物的物理性质
LEARNING OBJECTIVES 学习目标
■ Be able to explain the physical properties of ionic compounds in terms of their bonding and structure. ■ 能够从键合和结构方面解释离子化合物的物理性质。
Ionic compounds typically have the following physical properties: 离子化合物通常具有以下物理性质：
high melting temperatures 高熔点
brittleness 脆性
poor electrical conductivity when solid but good when molten 固体时导电性差，但熔融时导电性好
often soluble in water. 常溶于水。
HIGH MELTING TEMPERATURES 熔化温度高
Ionic solids consist of a giant lattice network of oppositely charged ions (see Topic 2B.2). There are many ions in the lattice and the combined electrostatic forces of attraction among all of the ions is large. 离子固体由带相反电荷的离子的巨大晶格网络组成（参见主题 2B.2）。晶格中有许多离子，所有离子之间的组合静电吸引力很大。
A large amount of energy is required to overcome the forces of attraction sufficiently for the ions to break free from the lattice and slide past one another. 需要大量的能量来克服足够的吸引力，使离子从晶格中挣脱出来并相互滑过。
BRITTLENESS 脆性
If a stress is applied to a crystal of an ionic solid, then the layers of ions may slide over one another. 如果对离子固体的晶体施加应力，则离子层可能会相互滑动。
A figA\mathbf{f i g} \mathbf{A} Effect of stress on an ionic crystal. A figA\mathbf{f i g} \mathbf{A} 应力对离子晶体的影响。
Ions of the same charge are now side by side and repel one another. The crystals break apart. 相同电荷的离子现在并排并相互排斥。晶体碎裂。
ELECTRICAL CONDUCTIVITY 电导率
Solid ionic compounds do not, in general, conduct electricity. This is because there are no delocalised electrons and the ions are also not free to move under the influence of an applied potential difference. 固体离子化合物通常不导电。这是因为没有离域电子，并且离子在施加的电位差的影响下也不能自由移动。
However, molten ionic compounds will conduct since the ions are now mobile and will migrate to the electrodes of opposite sign when a potential difference is applied. If direct current is used, the compound will undergo electrolysis as the ions are discharged at the electrodes. 然而，熔融离子化合物会导电，因为离子现在是可移动的，并且在施加电位差时会迁移到相反符号的电极上。如果使用直流电，当离子在电极处放电时，化合物将发生电解。
EXAM HINT 考试提示
Remember, oxidation always takes place at the anode. 请记住，氧化总是发生在阳极。
Aqueous solutions of ionic compounds also conduct electricity and undergo electrolysis, since the lattice breaks down into separate ions when the compound dissolves. 离子化合物的水溶液也导电并发生电解，因为当化合物溶解时晶格会分解成单独的离子。
DID YOU KNOW? 您是否了解？
As nearly always in chemistry, there are exceptions. Some ionic compounds do conduct electricity when solid. For example, solid lithium nitride (Li_(3)(N))\left(\mathrm{Li}_{3} \mathrm{~N}\right) will conduct electricity and is used in batteries for this reason. 就像化学中几乎总是一样，也有例外。一些离子化合物在固体时确实导电。例如，固体氮化 (Li_(3)(N))\left(\mathrm{Li}_{3} \mathrm{~N}\right) 锂会导电并因此用于电池。
SOLUBILITY 溶解度
Many ionic compounds are soluble in water. We will explain this solubility more fully in Topic 12A (Book 2: IAL), including the part played by entropy changes. 许多离子化合物溶于水。我们将在主题 12A（第 2 册：IAL）中更全面地解释这种溶解度，包括熵变化所起的作用。
At the moment, you just need to understand that the energy required to break apart the lattice structure and separate the ions can, in some instances, be supplied by the hydration of the separated ions produced. Both positive and negative ions are attracted to water molecules because of the polarity that water molecules possess (see Topic 3B for an explanation of polarity). 目前，您只需要了解，在某些情况下，分解晶格结构和分离离子所需的能量可以由产生的分离离子的水合提供。由于水分子所具有的极性，正离子和负离子都会被水分子吸引（有关极性的解释，请参阅主题 3B）。
The oxygen ends of the water molecules are attracted to positive ions. 水分子的氧端被正离子吸引。
The hydrogen ends of the water molecules are attracted to negative ions. 水分子的氢端被负离子吸引。
fig B Hydration of ions. 图 B 离子的水合。
hydration the process of water molecules being attracted to ions in solution and surrounding the ions; the oxygen ends of the water molecules are attracted to the positive ions (cations); the hydrogen ends of the water molecules are attracted to the negative ions (anions); hydration of ions is an exothermic process (i.e. heat energy is released) 水合：水分子被溶液中的离子吸引并包围离子的过程;水分子的氧端被正离子（阳离子）吸引;水分子的氢端被负离子（阴离子）吸引;离子的水合是一个放热过程（即释放热能）
LEARNING OBJECTIVES 学习目标
Know that a covalent bond is formed by the overlap of two atomic orbitals each containing a single electron.(shared) pair of electrons. 知道共价键是由两个原子轨道重叠形成的，每个原子轨道都包含一个电子。（共享的）电子对。
Understand the relationship between bond length and bond strength for covalent bonds. 了解共价键的键长和键强度之间的关系。
DID YOU KNOW? 您是否了解？
There is a fourth way that overlap can occur. An s- and p -orbital can overlap end on. 还有第四种方式可以发生重叠。s 轨道和 p 轨道可以重叠。 Delta\Delta fig B Overlap of an s- and a p-orbital to form a sigma bond. Delta\Delta 图 B s 轨道和 p 轨道重叠形成 σ 键。
This overlap, however, can only result from atoms of two different elements. This almost always leads to the formation of a variant of a covalent bond, known as a ‘polar’ covalent bond (see Topic 3B.2). 然而，这种重叠只能由两种不同元素的原子引起。这几乎总是导致共价键变体的形成，称为“极性”共价键（参见主题 3B.2）。
FORMATION OF COVALENT BONDS 共价键的形成
A covalent bond forms between two atoms when an atomic orbital containing a single electron from one atom overlaps with an atomic orbital, which also contains a single electron, of another atom. The two electrons in the area of overlap are the bonding electrons. They are sometimes referred to as a ‘shared pair of electrons’. The covalent bond is the electrostatic attraction between the two nuclei of the bonded atoms and the pair of electrons shared between them. 当包含一个原子的单个电子的原子轨道与另一个原子的原子轨道（也包含一个电子）重叠时，两个原子之间会形成共价键。重叠区域中的两个电子是键合电子。它们有时被称为“共享电子对”。共价键是键合原子的两个原子核与它们之间共享的一对电子之间的静电吸引力。
The atomic orbitals involved can be any of those found in the atoms, but we shall limit our discussion to those involving only s- and p-orbitals. 所涉及的原子轨道可以是在原子中发现的任何原子轨道，但我们将讨论仅限于那些只涉及 s 轨道和 p 轨道的轨道。
Fig A shows three ways in which these orbitals may overlap. 图 A 显示了这些轨道可能重叠的三种方式。
end on overlap of two s-orbitals (sigma bond) 在两个 S 轨道重叠时结束 （Sigma 键）
end on overlap of two p-orbitals (sigma bond) 两个 p 轨道重叠时结束（σ 键）
sideways overlap of two p-orbitals (pi bond) 两个 p 轨道的横向重叠 （Pi 键）
A fig A Formation of sigma bonds by end-on overlap of atomic orbitals and a pi bond by sideways overlap of p-orbitals. A 图 A 通过原子轨道的末端重叠形成 σ 键，通过 p 轨道的横向重叠形成 π 键。
An end-on overlap leads to the formation of sigma (sigma)(\sigma) bonds. This leads to the formation of a single covalent bond between the two atoms. 端接重叠导致 σ (sigma)(\sigma) 键的形成。这导致在两个原子之间形成单个共价键。
A sideways overlap of two p-orbitals leads to the formation of a pi (pi)(\pi) bond. A feature of a pi\pi bond is that it cannot form until a sigma\sigma bond has been formed. For this reason pi\pi bonds only exist between atoms that are joined by double or triple bonds. 两个 p 轨道的横向重叠导致 pi (pi)(\pi) 键的形成。 pi\pi 键的一个特点是在形成 sigma\sigma 键之前无法形成。因此， pi\pi 键仅存在于由双键或三键连接的原子之间。
The different types of orbital overlap are shown in the following examples. 以下示例显示了不同类型的轨道重叠。
EXAMPLE 1. HYDROGEN 示例 1.氢
A hydrogen atom has an electronic configuration of 1s^(1)1 \mathrm{~s}^{1}. 氢原子的电子排布为 1s^(1)1 \mathrm{~s}^{1} 。
When two hydrogen atoms bond together to form a hydrogen molecule, the two s-orbitals overlap to form a new molecular orbital. The two electrons then exist in this new orbital. The highest electron density is between the two nuclei. 当两个氢原子键合形成氢分子时，两个 s 轨道重叠形成新的分子轨道。然后这两个电子存在于这个新轨道中。最高的电子密度在两个原子核之间。
diagram showing orbital overlap 显示轨道重叠的图表
space filling model of a hydrogen molecule 氢分子的空间填充模型
fig C\mathbf{C} Formation of the sigma\sigma bond in hydrogen. C\mathbf{C} 图 氢中 sigma\sigma 键的形成。
EXAMPLE 2. CHLORINE 示例 2.氯
A chlorine atom has an electronic configuration of 1s^(2)2s^(2)2p^(6)3s^(2)3p_(x)^(2)3p_(y)^(2)3p_(z)^(1)1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p_{x}{ }^{2} 3 p_{y}{ }^{2} 3 p_{z}{ }^{1}. 氯原子的电子排布为 1s^(2)2s^(2)2p^(6)3s^(2)3p_(x)^(2)3p_(y)^(2)3p_(z)^(1)1 s^{2} 2 s^{2} 2 p^{6} 3 s^{2} 3 p_{x}{ }^{2} 3 p_{y}{ }^{2} 3 p_{z}{ }^{1} 。
When two chlorine atoms bond together, the two p orbitals (each containing a single electron) overlap. 当两个氯原子键合在一起时，两个 p 轨道（每个都包含一个电子）重叠。
diagram showing the orbital overlap 显示轨道重叠的图表
space filling model of a chlorine molecule 氯分子的空间填充模型 Delta\Delta fig D\mathbf{D} Formation of the sigma\sigma bond in chlorine. Delta\DeltaD\mathbf{D} 图 在氯中形成 sigma\sigma 键。
EXAMPLE 3. pi\pi BOND FORMATION 示例 3. pi\pi 键形成
Once a sigma\sigma bond has been formed, it is possible, in certain circumstances, for a pi\pi bond to form. 一旦形成 sigma\sigma 债券，在某些情况下，就有可能形成 pi\pi 债券。
The pi\pi bond results in a high electron density both above and below the molecule, as shown in fig E\mathbf{E}. 该 pi\pi 键导致分子上方和下方的高电子密度，如图 E\mathbf{E} 所示。
sideways overlap of pp-orbitals -orbitals 的 pp 横向重叠
fig E\mathbf{E} Formation of a pi\pi bond. E\mathbf{E} 图 键的 pi\pi 形成。
This is what happens in the ethene molecule. One of the bonds between the carbon atoms is a sigma\sigma bond; the other is a pi\pi bond. 这就是乙烯分子中发生的事情。碳原子之间的键之一是 sigma\sigma 键;另一个是 pi\pi 债券。
The pi\pi bond in ethene is weaker than the sigma\sigma bond. This is the reason for the increased reactivity of alkenes compared with alkanes, and why alkenes can easily undergo addition reactions. (See Topic 5 for more information.) 乙烯中的 pi\pi 键比 sigma\sigma 键弱。这就是烯烃与烷烃相比反应性增加的原因，也是烯烃容易发生加成反应的原因。（有关更多信息，请参阅主题 5。
The triple bond in the nitrogen molecule (N-=N)(\mathrm{N} \equiv \mathrm{N}) is made up of one sigma\sigma bond and two pi\pi bonds. 氮分子中的三键 (N-=N)(\mathrm{N} \equiv \mathrm{N}) 由一个 sigma\sigma 键和两个 pi\pi 键组成。
DID YOU KNOW? 您是否了解？
This view of the bonding in chlorine is very simple. 这种氯键合的观点非常简单。
An alternative theory describes the bonding as the overlap between two sp^(3)\mathrm{sp}^{3} hybrid orbitals. This theory is not included in this book, but we would encourage you to carry out your own research if you are interested. Look up ‘orbital hybridisation’. 另一种理论将键合描述为两个 sp^(3)\mathrm{sp}^{3} 杂化轨道之间的重叠。该理论未包含在本书中，但如果您有兴趣，我们鼓励您进行自己的研究。查找 'orbital hybridisation'。
The p-orbitals marked are those that are involved in the formation of the pi bonds. 标记的 p 轨道是参与 pi 键形成的轨道。
fig F Formation of the two pi\pi bonds in nitrogen. 图 F 两个 pi\pi 键在氮中的形成。
LEARNING TIP 学习小贴士
When making a comparison between bond length and bond strength, it is important to compare ‘like with like’, in other words, compare things that are the same or very similar. 在比较键长和键强度时，重要的是要 “同类 ”进行比较，换句话说，比较相同或非常相似的事物。
For example, the strength of the C-C\mathrm{C}-\mathrm{C} bond (347(kJ)mol^(-1))\left(347 \mathrm{~kJ} \mathrm{~mol}^{-1}\right) is greater than that of the N-N\mathrm{N}-\mathrm{N} bond (158(kJ)mol^(-1))\left(158 \mathrm{~kJ} \mathrm{~mol}^{-1}\right) despite being longer ( 0.154 nm compared with 0.145 nm ). In a molecule such as hydrazine (H_(2)(N)-NH_(2))\left(\mathrm{H}_{2} \mathrm{~N}-\mathrm{NH}_{2}\right), each nitrogen atom has a non-bonding (lone) pair of electrons and these repel one another, weakening the bond. In a molecule such as ethane (H_(3)C-CH_(3))\left(\mathrm{H}_{3} \mathrm{C}-\mathrm{CH}_{3}\right), the carbon atoms do not have any lone pairs. 例如，尽管键更长，但 C-C\mathrm{C}-\mathrm{C} 键 (347(kJ)mol^(-1))\left(347 \mathrm{~kJ} \mathrm{~mol}^{-1}\right) 的强度大于 N-N\mathrm{N}-\mathrm{N} 键 (158(kJ)mol^(-1))\left(158 \mathrm{~kJ} \mathrm{~mol}^{-1}\right) 的强度（0.154 nm 与 0.145 nm 相比）。在分子中，例如 肼 (H_(2)(N)-NH_(2))\left(\mathrm{H}_{2} \mathrm{~N}-\mathrm{NH}_{2}\right) ，每个氮原子都有一对非键合（孤）电子，这些电子相互排斥，削弱了键。在分子中，例如 乙烷 (H_(3)C-CH_(3))\left(\mathrm{H}_{3} \mathrm{C}-\mathrm{CH}_{3}\right) ，碳原子没有任何孤对电子。
BOND LENGTH AND BOND STRENGTH 键长和键强度
The bond length is the distance between the nuclei of two atoms that are covalently bonded together. 键长是共价键合在一起的两个原子的原子核之间的距离。
The strength of a covalent bond is measured in terms of the amount of energy required to break one mole of the bond in the gaseous state (see Topic 6). 共价键的强度是根据在气态下破坏一摩尔键所需的能量来衡量的（参见主题 6）。
Table A shows the relationship between the bond length and bond strength of a selection of covalent bonds. 表 A 显示了一系列共价键的键长和键强度之间的关系。
table A Relationship between bond length and bond strength for a range of covalent bonds. 表 A 一系列共价键的键长和键强度之间的关系。
The general relationship between bond length and bond strength, for bonds that are of a similar nature, is the shorter the bond, the greater the bond strength. This is a result of an increase in electrostatic attraction between the two nuclei and the electrons in the overlapping atomic orbitals. 对于具有相似性质的键，键长和键强度之间的一般关系是键越短，键强度越大。这是两个原子核与重叠原子轨道中的电子之间的静电吸引力增加的结果。
CHECKPOINT 检查站
Suggest a reason for the following trend in bond strengths: 提出债券强度出现以下趋势的原因：
The F-F\mathrm{F}-\mathrm{F} bond in fluorine is much shorter (0.142nm)(0.142 \mathrm{~nm}) than the Cl-Cl(0.199nm)\mathrm{Cl}-\mathrm{Cl}(0.199 \mathrm{~nm}) bond in chlorine, and yet it is much weaker ( 158kJmol^(-1)158 \mathrm{~kJ} \mathrm{~mol}^{-1} compared with 242kJmol^(-1)242 \mathrm{~kJ} \mathrm{~mol}^{-1} ). Suggest a reason for this. 氟中的 F-F\mathrm{F}-\mathrm{F} 键比氯中的 Cl-Cl(0.199nm)\mathrm{Cl}-\mathrm{Cl}(0.199 \mathrm{~nm}) 键短 (0.142nm)(0.142 \mathrm{~nm}) 得多，但它要弱得多（ 158kJmol^(-1)158 \mathrm{~kJ} \mathrm{~mol}^{-1} 与 242kJmol^(-1)242 \mathrm{~kJ} \mathrm{~mol}^{-1} 相比）。提出一个原因。
Suggest a reason why the sigma (sigma)(\sigma) bond between the two carbon atoms in the ethene molecule is stronger that the pi (pi)(\pi) bond. 提出乙烯分子中两个碳原子之间的 σ (sigma)(\sigma) 键比 pi (pi)(\pi) 键强的原因。
SUBJECT VOCABULARY 学科词汇
bond length the distance between the nuclei of two atoms that are covalently bonded together 键长 共价键合在一起的两个原子的原子核之间的距离
LEARNING OBJECTIVES 学习目标
Know that electronegativity is the ability of an atom to attract a bonding pair of electrons. 要知道，电负性是原子吸引一对键合电子的能力。 ◻\square Know that ionic and covalent bonding are the extremes of a continuum of bonding type and that electronegativity differences lead to bond polarity. ◻\square 要知道，离子键和共价键是键合类型连续体的极端，电负性差异会导致键极性。
Understand what a polar covalent bond is. 了解什么是极性共价键。
Understand that electron density maps for discrete (simple) molecules show that there is a high electron density between the nuclei of two covalently bonded atoms. 了解离散（简单）分子的电子密度图表明两个共价键合原子的原子核之间存在高电子密度。
WHAT IS ELECTRONEGATIVITY? 什么是电负性？
Electronegativity is the ability of an atom to attract a bonding pair of electrons. 电负性是原子吸引一对键合电子的能力。
The electronegativity of elements, in general: 元素的电负性，一般来说：
decreases down a group of the Periodic Table, that is, from top to bottom 在元素周期表中的一组向下减少，即从上到下
increases from left to right across a period. 在一段时间内从左到右增加。
This is demonstrated in the following section of the Periodic Table (fig A). 这在元素周期表的以下部分（图 A）中进行了演示。 Delta\Delta fig A\mathbf{A} able of electronegativities. Delta\Delta 无花果 A\mathbf{A} 能够 电负性。
DISTRIBUTION OF ELECTRON DENSITY 电子密度分布
If two atoms of the same element are bonded together by the overlap of atomic orbitals, the distribution of electron density between the two nuclei will be symmetrical. This is because the ability of each atom to attract the bonding pair of electrons is identical. 如果同一元素的两个原子通过原子轨道的重叠键合在一起，则两个原子核之间的电子密度分布将是对称的。这是因为每个原子吸引键合电子对的能力是相同的。
The diagram in fig B is an electron density map for chlorine (Cl_(2))\left(\mathrm{Cl}_{2}\right) : 图 B 中的图表是氯的电子密度图 (Cl_(2))\left(\mathrm{Cl}_{2}\right) ： Delta\Delta fig B Electron density map of a chlorine molecule. Delta\Delta 图 B 氯分子的电子密度图。
The diagram looks like a contour map. The contour lines correspond to electron density. You can think of them as showing how likely it is that a bonding electron will fall within that contour at a given instant in time. For a normal covalent bond, the contours are symmetrical around the nuclei. 该图看起来像一个等值线图。等值线对应于电子密度。您可以将它们视为显示键合电子在给定时刻落在该轮廓内的可能性有多大。对于正常的共价键，围绕原子核的轮廓是对称的。
LEARNING TIP 学习小贴士
Covalent bonds that are nonpolar are sometimes called ‘normal’ covalent bonds or ‘pure’ covalent bonds. This is to distinguish them from polar covalent bonds. 非极性的共价键有时称为“正常”共价键或“纯”共价键。这是为了将它们与极性共价键区分开来。
Both types of bond are formed by the overlap of atomic orbitals. 这两种类型的键都是由原子轨道的重叠形成的。
In both cases the overlapping area contains two electrons per bond formed. 在这两种情况下，重叠区域每个形成的键都包含两个电子。
POLAR COVALENT BONDS 极性共价键
However, if the two atoms bonded together are from elements that have different electronegativities, then the distribution of electron density will not be symmetrical about the two nuclei. This is shown in figC\mathbf{f i g} \mathbf{C} by the electron density map for the hydrogen chloride (HCl)(\mathrm{HCl}) molecule. 但是，如果键合在一起的两个原子来自不同具有不同电负性的元素，那么电子密度的分布将不会围绕两个原子核对称。这 figC\mathbf{f i g} \mathbf{C} 由氯化氢 (HCl)(\mathrm{HCl}) 分子的电子密度图显示。
fig C\mathbf{C} Electron density map of a hydrogen chloride molecule. C\mathbf{C} 图 氯化氢分子的电子密度图。
The contour lines are more closely spaced near to the chlorine atom, which is the atom with the higher electronegativity. 等值线在氯原子附近间隔更紧密，氯原子是电负性较高的原子。
Since the electron density is higher around the chlorine atom, that end of the molecule has acquired a slightly negative charge. This is represented by the symbol delta-\delta-. The other end of the molecule carries a slightly positive charge, represented by the symbol delta+\delta+. 由于氯原子周围的电子密度较高，因此分子的那一端获得了轻微的负电荷。这由符号 delta-\delta- 表示。分子的另一端带有轻微的正电荷，由符号 delta+\delta+ 表示。
A bond like this is called a polar covalent bond or sometimes just a ‘polar bond’. 像这样的键称为极性共价键，有时简称为“极性键”。
Another way of representing a polar covalent bond is to use an arrow to show the direction of electron drift. 表示极性共价键的另一种方法是使用箭头来显示电子漂移的方向。
HrarrCl\mathrm{H} \rightarrow \mathrm{Cl}
Other examples of polar covalent bonds are: 极性共价键的其他例子是：
Polar covalent bonds can be thought of as being between two ideals of bonding types. These ideals are: 极性共价键可以被认为是介于两种理想的键合类型之间。这些理想是：
pure (100%) covalent 纯 （100%） 共价
pure (100%) ionic. 纯 （100%） 离子。
Consider a polar covalent bond as a covalent bond that has some degree of ionic character. 将极性共价键视为具有一定程度离子特性的共价键。
If the electronegativity difference is large enough, then the main type of bonding is ionic. 如果电负性差异足够大，则主要的键合类型是离子键合。
A very approximate measure of the degree of ionic bonding in a compound is given in table A . 表 A 给出了化合物中离子键合程度的非常近似的量度。
table A Relationship between percentage ionic character and difference in electronegativity. 表 A 离子特性百分比与电负性差异之间的关系。
CHECKPOINT 检查站
Suggest why the electronegativity of fluorine is greater than that of chlorine, despite the fact that the nucleus of a chlorine atom contains more protons. 说明为什么氟的电负性大于氯，尽管氯原子的原子核包含更多的质子。
Ionic bonding and covalent bonding are two extremes of chemical bonding. Many compounds have bonding that is intermediate in character. 离子键和共价键是化学键的两个极端。许多化合物具有中等性质的键合。
(a) Giving an example in each case, explain what is meant by the terms: （a） 在每种情况下都举一个例子，解释这些术语的含义：
(i) ionic bonding, and (ii) covalent bonding. （i） 离子键，以及 （ii） 共价键。
(b) Select a compound that has bonding of an intermediate character and explain why it has this type of bonding. （b） 选择具有中间特性键合的化合物，并解释为什么它具有这种类型的键合。
Place the following bonds in order of decreasing polarity (i.e. place the most polar first). 按极性递减的顺序放置以下键（即，将极性最强的键放在最前面）。
Explain how you arrived at your answer. 解释您是如何得出答案的。
SUBJECT VOCABULARY 学科词汇
electronegativity the ability of an atom to attract a bonding pair of electrons in a covalent bond polar covalent bond a type of covalent bond between two atoms where the bonding electrons are unequally distributed; because of this, one atom carries a slight negative charge and the other a slight positive charge 电负性 原子在共价键中吸引一对键合电子的能力 极性共价键 两个原子之间的一种共价键，其中键合电子分布不均;因此，一个原子带有轻微的负电荷，另一个原子带有轻微的正电荷
LEARNING OBJECTIVES 学习目标
Understand what is meant by the term discrete (simple) molecule.Draw dot-and-cross diagrams to show electrons in discrete molecules with single, double and triple bonds.Draw displayed formulae to represent the bonding in discrete molecules.
DID YOU KNOW? 您是否了解？
Molecules are common in organic substances (and therefore biochemistry). They also make up most of the oceans and the atmosphere. However, ionic crystals (salts) and giant covalent crystals (network solids) are often made up of repeating unit cells that extend either in a plane (such as in graphene) or three-dimensionally (such as in diamond or sodium chloride). These substances are not composed of molecules. Solid metals are also not composed of molecules. 分子在有机物质中很常见（因此在生物化学中也很常见）。它们还构成了海洋和大气的大部分。然而，离子晶体（盐）和巨型共价晶体（网状固体）通常由重复的晶胞组成，这些晶胞要么在平面上延伸（如石墨烯），要么在三维面上延伸（如金刚石或氯化钠）。这些物质不是由分子组成的。固体金属也不是由分子组成的。 /_\\triangle fig A Dot-and-cross diagram for hydrogen with overlapping circles. /_\\triangle 图 A 具有重叠圆圈的氢的点十字图。
DISCRETE MOLECULES 离散分子
A discrete (simple) molecule is an electrically neutral group of two or more atoms held together by covalent bonds. 离散（简单）分子是由两个或多个原子组成的电中性基团，由共价键结合在一起。
DOT-AND-CROSS DIAGRAMS 点和交叉图
Covalent and polar covalent bonding in discrete molecules can be shown by dot-and-cross diagrams. 离散分子中的共价键和极性共价键可以用点叉图表示。
Fig A shows the example of hydrogen, H_(2)\mathrm{H}_{2}. 图 A 显示了氢 的例子。 H_(2)\mathrm{H}_{2}
Further examples of dot-and-cross diagrams are shown in table A. 表 A 显示了点交叉图的更多示例。
SUBSTANCE 物质
table A Dot-and-cross diagrams for water, ammonia and methane. 表 A 水、氨和甲烷的点和交叉图。
EXAM HINT 考试提示
When drawing a molecule such as chloromethane, do not forget to show all of the non-bonding electrons on the chlorine atom. 绘制氯甲烷等分子时，不要忘记显示氯原子上的所有非键合电子。
THE OCTET RULE 八位组规则
You might read that in order to form a stable compound, the outer shell of each atom must have the same number of electrons as the outer shell of a noble gas. In most cases this will be eight electrons. This has led to a rule that is often referred to as the ‘octet rule’. 您可能会读到，为了形成稳定的化合物，每个原子的外壳必须具有与惰性气体外壳相同的电子数。在大多数情况下，这将是八个电子。这导致了通常被称为“八位字节规则”的规则。
This is not always true, as you can see from the examples in table B. In each case, the outer shell of the central atom of the molecule does not contain eight electrons. 这并不总是正确的，从表 B 中的示例中可以看出。在每种情况下，分子中心原子的外壳不包含八个电子。
SUBSTANGE
DOT-AND-CROSS DIAGRAM 点交叉图
NUMBER OF ELECTRONS AROUND 周围的电子数
CENTRAL ATOM 中央原子
SUBSTANGE DOT-AND-CROSS DIAGRAM NUMBER OF ELECTRONS AROUND
CENTRAL ATOM | SUBSTANGE | DOT-AND-CROSS DIAGRAM | NUMBER OF ELECTRONS AROUND |
| :--- | :---: | :---: |
| CENTRAL ATOM | | |
table B Examples breaking the octet rule. 表 B 打破八位字节规则的示例。
DOT-AND-CROSS DIAGRAMS OF MOLECULES CONTAINING MULTIPLE BONDS 包含多个键的分子的点和交叉图
Table C\mathbf{C} shows the dot-and-cross diagrams for three molecules (O_(2),N_(2),CO_(2))\left(\mathrm{O}_{2}, \mathrm{~N}_{2}, \mathrm{CO}_{2}\right) that contain a double or triple bond. 表格 C\mathbf{C} 显示了包含双键或三键的三个分子 (O_(2),N_(2),CO_(2))\left(\mathrm{O}_{2}, \mathrm{~N}_{2}, \mathrm{CO}_{2}\right) 的点交叉图。
Table C\mathbf{C} gives some examples of dot-and-cross diagrams together with the displayed formulae. 表格 C\mathbf{C} 给出了一些点叉图的示例以及显示的公式。
A displayed (full structural) formula shows each bonding pair as a line drawn between the two atoms involved. 显示的（完整结构）公式将每个键合对显示为在所涉及的两个原子之间绘制的一条线。
LEARNING OBJECTIVES 学习目标
Know that in a dative covalent bond both electrons in the bond are supplied by only one of the atoms involved in forming the bond.
Be able to draw dot-and-cross diagrams for some molecules and ions that contain dative covalent bonds, including Al_(2)Cl_(6)\mathrm{Al}_{2} \mathrm{Cl}_{6} and the ammonium ion. 能够为一些包含配格共价键的分子和离子绘制点交叉图，包括 Al_(2)Cl_(6)\mathrm{Al}_{2} \mathrm{Cl}_{6} 和铵离子。
DATIVE COVALENT BOND FORMATION 配向共价键形成
A dative covalent bond is formed when an empty orbital of one atom overlaps with an orbital containing a non-bonding pair (lone pair) of electrons of another atom. 当一个原子的空轨道与包含另一个原子的非键合电子对（孤对）的轨道重叠时，就会形成配位共价键。
The bond is often represented by an arrow from the atom providing the pair of electrons, to the atom with the empty orbital. Below are three examples of dative covalent bonds. 键通常由从提供电子对的原子到具有空轨道的原子的箭头表示。以下是配格共价键的三个例子。
THE HYDROXONIUM ION, H_(3)O^(+)\mathrm{H}_{3} \mathrm{O}^{+} HYDROXONIUM 离子， H_(3)O^(+)\mathrm{H}_{3} \mathrm{O}^{+}
The dot-and-cross diagram and the displayed formula of a hydroxonium ion are shown in fig A . 点交叉图和显示的氢氧离子公式如图 A 所示。
C[CH-]OC
A fig A Dot-and-cross diagram and displayed formula for the hydroxonium ion. 图 A 点和交叉图和显示的氢氧离子的公式。
The empty 1 s orbital of the H^(+)\mathrm{H}^{+}ion overlaps with the orbital of the oxygen atom that contains the lone pair of electrons. H^(+)\mathrm{H}^{+} 离子的空 1 s 轨道与包含孤对电子的氧原子的轨道重叠。
THE AMMONIUM ION, NH_(4)^(+)\mathrm{NH}_{4}{ }^{+} 铵离子， NH_(4)^(+)\mathrm{NH}_{4}{ }^{+}
The dot-and-cross diagram and the displayed formula of an ammonium ion are shown in fig B. 铵离子的点交叉图和显示的公式如图 B 所示。
fig B Dot-and-cross diagram and displayed formula for the ammonium ion. 图 B 点十字图和显示的铵离子公式。
The empty 1 s orbital of the H^(+)\mathrm{H}^{+}ion overlaps with the orbital of the nitrogen atom that contains the lone pair of electrons. H^(+)\mathrm{H}^{+} 离子的空 1 s 轨道与包含孤对电子的氮原子的轨道重叠。
The aluminium atom in the AlCl_(3)\mathrm{AlCl}_{3} molecule has only six electrons in its outer shell and so has an empty orbital (fig C). AlCl_(3)\mathrm{AlCl}_{3} 分子中的铝原子在其外壳中只有六个电子，因此有一个空轨道（图 C）。 /_\\triangle fig C\mathbf{C} Dot-and-cross diagram for aluminium chloride. /_\\triangle 图 氯化铝的 C\mathbf{C} 点十字图。
In the gas phase, just above its sublimation temperature, aluminium chloride exists as Al_(2)Cl_(6)\mathrm{Al}_{2} \mathrm{Cl}_{6} molecules (fig D). 在气相中，略高于其升华温度，氯化铝以分子形式 Al_(2)Cl_(6)\mathrm{Al}_{2} \mathrm{Cl}_{6} 存在（图 D）。
Two AlCl_(3)\mathrm{AlCl}_{3} molecules bond together. One of the atomic orbitals of a chlorine atom of one AlCl_(3)\mathrm{AlCl}_{3} molecule that contains a lone pair overlaps with the empty orbital of the aluminium atom of a second AlCl_(3)\mathrm{AlCl}_{3} molecule. The same happens between the chlorine atom of the second molecule and the aluminium atom of the first molecule. 两个 AlCl_(3)\mathrm{AlCl}_{3} 分子键合在一起。包含一个 AlCl_(3)\mathrm{AlCl}_{3} 孤对电子的分子的氯原子的原子轨道之一与第二个 AlCl_(3)\mathrm{AlCl}_{3} 分子的铝原子的空轨道重叠。第二个分子的氯原子和第一个分子的铝原子之间也会发生同样的情况。
One chlorine atom from each molecule acts as a bridge connecting the two molecules with dative covalent bonds. 每个分子中的一个氯原子充当用配位共价键连接两个分子的桥梁。
fig D Displayed formula for the aluminium dimer. 图 D 显示铝二聚体的公式。
OHECKPOINT
(a) Draw a dot-and-cross diagram for a molecule of NH_(3)\mathrm{NH}_{3} and a molecule of BF_(3)\mathrm{BF}_{3}. （a） 为 的分子 NH_(3)\mathrm{NH}_{3} 和 的分子绘制点十字图 BF_(3)\mathrm{BF}_{3} 。
(b) Draw a dot-and-cross diagram for a molecule of NH_(3)*BF_(3)\mathrm{NH}_{3} \cdot \mathrm{BF}_{3}. （b） 为 的分子绘制点十字图 NH_(3)*BF_(3)\mathrm{NH}_{3} \cdot \mathrm{BF}_{3} 。
Draw a dot-and-cross diagram and displayed formula for the AlCl_(4)^(-)\mathrm{AlCl}_{4}^{-}ion and identify the dative covalent bond. 绘制一个点交叉图并显示离子的 AlCl_(4)^(-)\mathrm{AlCl}_{4}^{-} 公式，并确定配格共价键。
One way of describing the bonding in a molecule of carbon monoxide (CO) is to state that it contains two covalent bonds and one dative bond. Using this description, draw a dot-and-cross diagram and displayed formula for a molecule of carbon monoxide. 描述一氧化碳 （CO） 分子中键合的一种方法是说明它包含两个共价键和一个配位键。使用此描述，绘制一个点交叉图并显示一氧化碳分子的公式。
SUBJECT VOGABULARY 主题词汇
dative covalent bond the bond formed when an empty orbital of one atom overlaps with an orbital containing a lone pair of electrons of another atom 配位共价键 当一个原子的空轨道与包含另一个原子的孤对电子的轨道重叠时形成的键
3C3 C 1 SHAPES OF MOLECULES AND IONS 3C3 C 1 分子和离子的形状
LEARNING OBJECTIVES 学习目标
■ Understand the principles of the electron-pair repulsion theory, used to interpret and predict the shapes of simple molecules and ions. ■ 了解电子对排斥理论的原理，用于解释和预测简单分子和离子的形状。
Understand the term bond angle.Know and be able to explain the shapes of, and bond angles in, BeCl_(2),BCl_(3),CH_(4),NH_(3),NH_(4)^(+),H_(2)O,CO_(2)\mathrm{BeCl}_{2}, \mathrm{BCl}_{3}, \mathrm{CH}_{4}, \mathrm{NH}_{3}, \mathrm{NH}_{4}{ }^{+}, \mathrm{H}_{2} \mathrm{O}, \mathrm{CO}_{2}, gaseous PCl_(5),SF_(6)\mathrm{PCl}_{5}, \mathrm{SF}_{6} and C_(2)H_(4)\mathrm{C}_{2} \mathrm{H}_{4}. 了解术语键角。了解并能够解释 、 BeCl_(2),BCl_(3),CH_(4),NH_(3),NH_(4)^(+),H_(2)O,CO_(2)\mathrm{BeCl}_{2}, \mathrm{BCl}_{3}, \mathrm{CH}_{4}, \mathrm{NH}_{3}, \mathrm{NH}_{4}{ }^{+}, \mathrm{H}_{2} \mathrm{O}, \mathrm{CO}_{2} 、 气态 PCl_(5),SF_(6)\mathrm{PCl}_{5}, \mathrm{SF}_{6} 和 C_(2)H_(4)\mathrm{C}_{2} \mathrm{H}_{4} 的形状和键合角。
■ Be able to apply the electron-pair repulsion theory to predict the shapes of, and bond angles in, molecules and ions analogous to those mentioned above. ■ 能够应用电子对排斥理论来预测分子和离子的形状和键角，类似于上述内容。
ELECTRON PAIR REPULSION THEORY 电子对排斥理论
The electron pair repulsion (EPR) theory states that: 电子对排斥 （EPR） 理论指出：
the shape of a molecule or ion is caused by repulsion between the pairs of electrons, both bond pairs and lone (non-bonding) pairs, that surround the central atom 分子或离子的形状是由围绕中心原子的电子对之间的排斥引起的，包括键对和孤（非键）对
the electron pairs arrange themselves around the central atom so that the repulsion between them is at a minimum 电子对围绕中心原子排列，因此它们之间的排斥最小
This theory is sometimes also called the valence shell electron pair repulsion theory, abbreviated to VSEPR. 该理论有时也称为价壳电子对排斥理论，缩写为 VSEPR。
The first two rules are used to obtain the basic shape of the molecule or ion. The third rule is used to estimate values for the bond angles. 前两条规则用于获得分子或离子的基本形状。第三条规则用于估计键角的值。
THE SHAPES OF MOLECULES AND IONS 分子和离子的形状
To obtain the shape of a molecule or ion it is first necessary to obtain the number of bond pairs and lone pairs of electrons around the central atom. 要获得分子或离子的形状，首先需要获得中心原子周围的键对数和孤对电子数。
The easiest way to do this is by drawing a dot-and-cross diagram. You can then apply the guidelines listed in table A. 最简单的方法是绘制一个点交叉图。然后，您可以应用表 A 中列出的准则。
MOLECULES WITH MULTIPLE BONDS 具有多个键的分子
To determine the shape of a molecule containing one or more multiple bonds, treat each multiple bond as if it contained only one pair of electrons. 要确定包含一个或多个多重键的分子的形状，请将每个多重键视为仅包含一对电子。
EXAMPLE 1. CARBON DIOXIDE, CO_(2)\mathrm{CO}_{2} 示例 1.二氧化碳 CO_(2)\mathrm{CO}_{2}
The displayed formula for carbon dioxide is O=C=O\mathrm{O}=\mathrm{C}=\mathrm{O}. There are no lone pairs on the carbon atom. 显示的二氧化碳公式为 O=C=O\mathrm{O}=\mathrm{C}=\mathrm{O} 。碳原子上没有孤对电子。
If each double bond is treated as an electron pair, then the molecule is linear, like BeCl_(2)\mathrm{BeCl}_{2}. 如果将每个双键视为电子对，则分子是线性的，如 BeCl_(2)\mathrm{BeCl}_{2} 。
NUMBER OF BOND PAIRS 键对数
NUMBER OF LONE PAIRS 孤对数
SHAPE
EXAMPLE
2
0
linear 线性
Cl-Be-Cl\mathrm{Cl}-\mathrm{Be}-\mathrm{Cl}
3
0
三角平面
trigonal
planar
trigonal
planar| trigonal |
| :--- |
| planar |
ClB(Cl)Cl
4
0
tetrahedral 四面体的
C
5
0
trigonal bipyramidal 三角双锥体
Cl[Pb-](Cl)(Cl)(Cl)Cl
6
0
octahedral 八面体的
F[Sb-](F)(F)(F)(F)F
3
1
trigonal pyramidal 三角锥体
[1H]N[1H]
2
2
V-shaped V 形
[CH]=[CH]
NUMBER OF BOND PAIRS NUMBER OF LONE PAIRS SHAPE EXAMPLE
2 0 linear Cl-Be-Cl
3 0 "trigonal
planar" ClB(Cl)Cl
4 0 tetrahedral C
5 0 trigonal bipyramidal Cl[Pb-](Cl)(Cl)(Cl)Cl
6 0 octahedral F[Sb-](F)(F)(F)(F)F
3 1 trigonal pyramidal [1H]N[1H]
2 2 V-shaped [CH]=[CH]| NUMBER OF BOND PAIRS | NUMBER OF LONE PAIRS | SHAPE | EXAMPLE |
| :---: | :---: | :---: | :---: |
| 2 | 0 | linear | $\mathrm{Cl}-\mathrm{Be}-\mathrm{Cl}$ |
| 3 | 0 | trigonal <br> planar | <smiles>ClB(Cl)Cl</smiles> |
| 4 | 0 | tetrahedral | <smiles>C</smiles> |
| 5 | 0 | trigonal bipyramidal | <smiles>Cl[Pb-](Cl)(Cl)(Cl)Cl</smiles> |
| 6 | 0 | octahedral | <smiles>F[Sb-](F)(F)(F)(F)F</smiles> |
| 3 | 1 | trigonal pyramidal | <smiles>[1H]N[1H]</smiles> |
| 2 | 2 | V-shaped | <smiles>[CH]=[CH]</smiles> |
table A Shapes of molecules. 表 A 分子的形状。
EXAMPLE 2. ETHENE, C_(2)H_(4)\mathrm{C}_{2} \mathrm{H}_{4} 示例 2.乙烯 C_(2)H_(4)\mathrm{C}_{2} \mathrm{H}_{4}
The displayed formula of ethene is: 显示的乙烯公式为：
C=C
There are no lone pairs on either carbon atom. 两个碳原子上都没有孤对电子。
Treating each double bond as an electron pair produces a planar molecule with 120^(@)120^{\circ} bond angles. 将每个双键视为电子对会产生具有 120^(@)120^{\circ} 键角的平面分子。
THE BOND ANGLES IN MOLECULES AND IONS 分子和离子中的键角
Table B shows the bond angles of a range of molecules and ions. 表 B 显示了一系列分子和离子的键角。
Lone pair-bond pair repulsion is greater than bond pair-bond pair repulsion, so the angle is slightly less than 109.5^(@)109.5^{\circ}.
Trigonal pyramidal, e.g. NH_(3)
The bond angle is 107^(@).
Lone pair-bond pair repulsion is greater than bond pair-bond pair repulsion, so the angle is slightly less than 109.5^(@).| Trigonal pyramidal, e.g. $\mathrm{NH}_{3}$ |
| :--- |
| The bond angle is $107^{\circ}$. |
| Lone pair-bond pair repulsion is greater than bond pair-bond pair repulsion, so the angle is slightly less than $109.5^{\circ}$. |
V 形，例如 H_(2)O\mathrm{H}_{2} \mathrm{O}
键角为104.5^（@）104.5^{\circ}.
孤对-孤对排斥大于孤对-键对排斥，因此键角进一步从109.5^（@）109.5^{\circ}，并且略小于107^（@）107^{\circ} 在NH_（3）\mathrm{NH}_{3}。
V-shaped, e.g. H_(2)O\mathrm{H}_{2} \mathrm{O}
The bond angle is 104.5^(@)104.5^{\circ}.
Lone pair-lone pair repulsion is greater than lone pair-bond pair repulsion, so the bond angle is even further depressed from 109.5^(@)109.5^{\circ}, and is slightly less than the 107^(@)107^{\circ} in NH_(3)\mathrm{NH}_{3}.
V-shaped, e.g. H_(2)O
The bond angle is 104.5^(@).
Lone pair-lone pair repulsion is greater than lone pair-bond pair repulsion, so the bond angle is even further depressed from 109.5^(@), and is slightly less than the 107^(@) in NH_(3).| V-shaped, e.g. $\mathrm{H}_{2} \mathrm{O}$ |
| :--- |
| The bond angle is $104.5^{\circ}$. |
| Lone pair-lone pair repulsion is greater than lone pair-bond pair repulsion, so the bond angle is even further depressed from $109.5^{\circ}$, and is slightly less than the $107^{\circ}$ in $\mathrm{NH}_{3}$. |
Trigonal bipyramidal, e.g. PCl_(5)\mathrm{PCl}_{5}
There are two bond angles: 90^(@)90^{\circ} and 120^(@)120^{\circ}.
Trigonal bipyramidal, e.g. PCl_(5)
There are two bond angles: 90^(@) and 120^(@).| Trigonal bipyramidal, e.g. $\mathrm{PCl}_{5}$ |
| :--- |
| There are two bond angles: $90^{\circ}$ and $120^{\circ}$. |
There are two bond angles: 90^(@)90^{\circ} and 180^(@)180^{\circ}.
The angle between the bonds of two fluorine atoms opposite one another is 180^(@)180^{\circ}.
Octahedral, e.g. SF_(6)
There are two bond angles: 90^(@) and 180^(@).
The angle between the bonds of two fluorine atoms opposite one another is 180^(@).| Octahedral, e.g. $\mathrm{SF}_{6}$ |
| :--- |
| There are two bond angles: $90^{\circ}$ and $180^{\circ}$. |
| The angle between the bonds of two fluorine atoms opposite one another is $180^{\circ}$. |
As with CH_(4)\mathrm{CH}_{4}, the bond angles are 109.5^(@)109.5^{\circ}.
Note the change from 107^(@)107^{\circ} in ammonia to 109.5^(@)109.5^{\circ} in the ammonium ion.
Tetrahedral, e.g. NH_(4)^(+)
As with CH_(4), the bond angles are 109.5^(@).
Note the change from 107^(@) in ammonia to 109.5^(@) in the ammonium ion.| Tetrahedral, e.g. $\mathrm{NH}_{4}^{+}$ |
| :--- |
| As with $\mathrm{CH}_{4}$, the bond angles are $109.5^{\circ}$. |
| Note the change from $107^{\circ}$ in ammonia to $109.5^{\circ}$ in the ammonium ion. |
"Linear, e.g. BeCl_(2)
The bond angle is 180^(@)." "Trigonal planar, e.g. BCl_(3)
The bond angle is 120^(@)."
"Tetrahedral, e.g. CH_(4)
The bond angle is 109.5^(@)." "Trigonal pyramidal, e.g. NH_(3)
The bond angle is 107^(@).
Lone pair-bond pair repulsion is greater than bond pair-bond pair repulsion, so the angle is slightly less than 109.5^(@)."
"V-shaped, e.g. H_(2)O
The bond angle is 104.5^(@).
Lone pair-lone pair repulsion is greater than lone pair-bond pair repulsion, so the bond angle is even further depressed from 109.5^(@), and is slightly less than the 107^(@) in NH_(3)." "Trigonal bipyramidal, e.g. PCl_(5)
There are two bond angles: 90^(@) and 120^(@)."
"Octahedral, e.g. SF_(6)
There are two bond angles: 90^(@) and 180^(@).
The angle between the bonds of two fluorine atoms opposite one another is 180^(@)." "Tetrahedral, e.g. NH_(4)^(+)
As with CH_(4), the bond angles are 109.5^(@).
Note the change from 107^(@) in ammonia to 109.5^(@) in the ammonium ion."| Linear, e.g. $\mathrm{BeCl}_{2}$ <br> The bond angle is $180^{\circ}$. | Trigonal planar, e.g. $\mathrm{BCl}_{3}$ <br> The bond angle is $120^{\circ}$. |
| :---: | :---: |
| Tetrahedral, e.g. $\mathrm{CH}_{4}$ <br> The bond angle is $109.5^{\circ}$. | Trigonal pyramidal, e.g. $\mathrm{NH}_{3}$ <br> The bond angle is $107^{\circ}$. <br> Lone pair-bond pair repulsion is greater than bond pair-bond pair repulsion, so the angle is slightly less than $109.5^{\circ}$. |
| V-shaped, e.g. $\mathrm{H}_{2} \mathrm{O}$ <br> The bond angle is $104.5^{\circ}$. <br> Lone pair-lone pair repulsion is greater than lone pair-bond pair repulsion, so the bond angle is even further depressed from $109.5^{\circ}$, and is slightly less than the $107^{\circ}$ in $\mathrm{NH}_{3}$. | Trigonal bipyramidal, e.g. $\mathrm{PCl}_{5}$ <br> There are two bond angles: $90^{\circ}$ and $120^{\circ}$. |
| Octahedral, e.g. $\mathrm{SF}_{6}$ <br> There are two bond angles: $90^{\circ}$ and $180^{\circ}$. <br> The angle between the bonds of two fluorine atoms opposite one another is $180^{\circ}$. | Tetrahedral, e.g. $\mathrm{NH}_{4}^{+}$ <br> As with $\mathrm{CH}_{4}$, the bond angles are $109.5^{\circ}$. <br> Note the change from $107^{\circ}$ in ammonia to $109.5^{\circ}$ in the ammonium ion. |
table B The bond angles of a range of molecules and ions. 表 B 一系列分子和离子的键角。
CHECKPOINT 检查站
(a) Draw a diagram to show the shape of each of the following molecules: （a） 画一个图表来显示以下每个分子的形状：
(i) H_(2)S\mathrm{H}_{2} \mathrm{~S} （一） H_(2)S\mathrm{H}_{2} \mathrm{~S}
(ii) PH_(3)\mathrm{PH}_{3} （二） PH_(3)\mathrm{PH}_{3}
(iii) PF_(3)\mathrm{PF}_{3} （三） PF_(3)\mathrm{PF}_{3}
(iv) SCl_(2)\mathrm{SCl}_{2} （四） SCl_(2)\mathrm{SCl}_{2}
(v) AsF_(5)\mathrm{AsF}_{5} （五） AsF_(5)\mathrm{AsF}_{5}
(vi) HCN （vi） HCN
(vii) SO_(2)\mathrm{SO}_{2} （七） SO_(2)\mathrm{SO}_{2}
(b) Give the name of each shape. （b） 给出每个形状的名称。
Solid phosphorus pentachloride has the formula [PCl_(4)]^(+)(PCl_(6)]^(-)\left[\mathrm{PCl}_{4}\right]^{+}\left(\mathrm{PCl}_{6}\right]^{-}. 固体五氯化磷的分子式 [PCl_(4)]^(+)(PCl_(6)]^(-)\left[\mathrm{PCl}_{4}\right]^{+}\left(\mathrm{PCl}_{6}\right]^{-} 为 。
(a) Draw a diagram to show the shape of each ion. （a） 画一个图表来显示每个离子的形状。
(b) State the bond angles present in each ion. （b） 说明每个离子中存在的键角。
Two possible ways of arranging the bonding pairs and lone pairs of electrons in a molecule of XeF_(4)\mathrm{XeF}_{4} are: 在分子 XeF_(4)\mathrm{XeF}_{4} 中排列键对和孤对电子的两种可能方法是：
and 和
F[Te](F)(F)(F)(F)F
Suggest which of these two arrangements is the more likely and justify your answer. 建议这两种安排中哪一种更有可能，并证明您的答案是合理的。
SUBJECT VOCABULARY 学科词汇
electron pair repulsion (EPR) theory the electron pairs on the central atom of a molecule or ion arrange themselves in order to create the minimum repulsion between them; lone pair-lone pair repulsion is greater than lone pair-bond repulsion, which in turn is greater than bond pair-bond pair repulsion 电子对排斥 （EPR） 理论：分子或离子中心原子上的电子对自行排列，以便在它们之间产生最小的排斥;孤对-孤对-孤对排斥大于孤对-键排斥，而孤对-键对排斥又大于键对-键对排斥
LEARNING OBJECTIVES 学习目标
Understand the difference between non-polar and polar molecules and be able to predict whether or not a given molecule is likely to be polar. 了解非极性分子和极性分子之间的区别，并能够预测给定分子是否可能是极性的。
SHAPE AND POLARITY 形状和极性
The drift of bonded electrons towards the more electronegative element (see Topic 3B.2) results in a separation of charge. This separation of charge is called a dipole. 键合电子向电负性更强的元素漂移（参见主题 3B.2）导致电荷分离。这种电荷分离称为偶极子。
Each of the bonds in a molecule has its own dipole associated with it. The overall dipole of a molecule depends on its shape. Depending on the relative angles between the bonds, the individual dipoles can either reinforce one another or cancel out each other. 分子中的每个键都有自己的偶极子与之相关。分子的总偶极子取决于它的形状。根据键之间的相对角度，各个偶极子可以相互增强或相互抵消。
If the cancellation is complete, the resulting molecule will have no overall dipole and is said to be ‘non-polar’. 如果抵消完成，则得到的分子将没有总偶极子，称为“非极性”。
If the dipoles reinforce one another, the molecule will possess an overall dipole and is said to be ‘polar’. 如果偶极子相互增强，则该分子将具有一个整体偶极子，称为“极性”。
DIATOMIC MOLECULES 双原子分子
Hydrogen and chlorine are examples of diatomic molecules that are non-polar. The two atoms in each molecule are the same and so have the same electronegativity. The distribution of electron density of the bonding electrons in either molecule is totally symmetrical (see Topic 3B.2). The bond in each is therefore nonpolar, making the molecules non-polar. 氢和氯是非极性双原子分子的例子。每个分子中的两个原子相同，因此具有相同的电负性。任一分子中键合电子的电子密度分布是完全对称的（参见主题 3B.2）。因此，每个中的键都是非极性的，使分子成为非极性的。
However, the bond in the hydrogen chloride molecule is polar because the electronegativity of chlorine (3.0) is greater than that of hydrogen (2.1). 然而，氯化氢分子中的键是极性的，因为氯的电负性 （3.0） 大于氢的电负性 （2.1）。 H^(delta+)rarrCl^(delta-)\mathrm{H}^{\delta+} \rightarrow \mathrm{Cl}^{\delta-}
Since this is the only polar bond in the molecule, the molecule itself is polar. 由于这是分子中唯一的极性键，因此分子本身是极性的。
The following symbol is used to represent a dipole: ↛\nrightarrow 以下符号用于表示偶极子： ↛\nrightarrow
The dipole in the hydrogen chloride molecule is shown as: 氯化氢分子中的偶极子表示为：
Both bonds in the carbon dioxide molecule are polar, but the dipoles cancel out one another. 二氧化碳分子中的两个键都是极性的，但偶极子会相互抵消。
{:[O^(delta-)=C^(delta+)=O^(delta-)],[ larr+longrightarrow],[∼figA" Dipoles in carbon dioxide. "]:}\begin{aligned}
& \mathrm{O}^{\delta-}=\mathrm{C}^{\delta+}=\mathrm{O}^{\delta-} \\
& \leftarrow+ \longrightarrow \\
& \mathbb{\sim} \mathbf{f i g} \mathbf{A} \text { Dipoles in carbon dioxide. }
\end{aligned}
The carbon dioxide molecule is therefore non-polar. 因此，二氧化碳分子是非极性的。
2. TRIGONAL PLANAR MOLECULES 2. 三方平面分子
Example: boron chloride, BCl_(3)\mathrm{BCl}_{3} 示例：氯化硼， BCl_(3)\mathrm{BCl}_{3}
fig B Dipoles in boron trichloride. 图 B 三氯化硼中的偶极子。
All three B—Cl\mathrm{B} — \mathrm{Cl} bonds are polar, but because the molecule is symmetrical the dipoles cancel out one another. The molecule is non-polar. 所有三个 B—Cl\mathrm{B} — \mathrm{Cl} 键都是极性的，但由于分子是对称的，偶极子会相互抵消。该分子是非极性的。
3. TETRAHEDRAL MOLECULES 3. 四面体分子
Example 1: tetrachloromethane, CCl_(4)\mathrm{CCl}_{4} 实施例 1：四氯甲烷， CCl_(4)\mathrm{CCl}_{4}
/_\\triangle fig C Dipoles in tetrachloromethane. /_\\triangle 图 C 四氯甲烷中的偶极子。
All four C-Cl\mathrm{C}-\mathrm{Cl} bonds are polar, but because the molecule is symmetrical the dipoles cancel out one another. The molecule is non-polar. 所有四个 C-Cl\mathrm{C}-\mathrm{Cl} 键都是极性的，但由于分子是对称的，偶极子会相互抵消。该分子是非极性的。
Example 2: trichloromethane, CHCl_(3)\mathrm{CHCl}_{3} 实施例 2：三氯甲烷， CHCl_(3)\mathrm{CHCl}_{3}
fig D Dipoles in trichloromethane. 图 D 三氯甲烷中的偶极子。
All four bonds are polar but, although the molecule is symmetrical, the dipoles reinforce one another and so the molecule is polar. 所有四个键都是极性的，但是，尽管分子是对称的，但偶极子相互增强，因此分子是极性的。
All three N-H\mathrm{N}-\mathrm{H} bonds are polar and the dipoles reinforce one another. The molecule is polar. 所有三个 N-H\mathrm{N}-\mathrm{H} 键都是极性的，偶极子相互增强。分子是极性的。
fig E\mathbf{E} Dipoles in ammonia. 无花果 氨中的 E\mathbf{E} 偶极子。
fig F\mathbf{F} Dipoles in water. 图 水中的 F\mathbf{F} 偶极子。
Both O-H\mathrm{O}-\mathrm{H} bonds are polar and the dipoles reinforce one another. The molecule is polar. 两个 O-H\mathrm{O}-\mathrm{H} 键都是极性的，偶极子相互增强。分子是极性的。
ADDITIONAL READING 补充阅读
Dipole moments 偶极矩
The polarity of the molecule is measured by its dipole moment. 分子的极性由其偶极矩来测量。
For a diatomic molecule such as hydrogen chloride, the dipole moment is defined as the difference in charge (i.e. the difference in magnitude between delta+\delta+ and delta-\delta- ) multiplied by the distance of separation between the charges. 对于氯化氢等双原子分子，偶极矩定义为电荷差（即 和 delta-\delta- 之间的 delta+\delta+ 大小差）乘以电荷之间的分离距离。
For a polyatomic molecule, it is more complicated because the polarities of each bond have to be taken into account, as well as any lone pairs on the central atom. 对于多原子分子，它更复杂，因为必须考虑每个键的极性，以及中心原子上的任何孤对电子。
Table A gives the dipole moments of a number of molecules. 表 A 给出了许多分子的偶极矩。
table A Dipole moments of some molecules. 表 A 一些分子的偶极矩。
The unit of dipole moment is the Debye, symbol D. You do not need to understand this unit; just focus on the magnitude of the numbers. The larger the number, the more polar the molecule. 偶极矩的单位是德拜，符号 D。您无需了解此单元;只需关注数字的大小。数字越大，分子的极性越强。
CHECKPOINT 检查站
A bond between two atoms in a molecule may possess a dipole. 分子中两个原子之间的键可能具有偶极子。
(a) Explain how this dipole arises. （a） 解释这个偶极子是如何产生的。
(b) Some bonds that you are likely to meet in organic chemistry are listed. Which of these bonds are likely to possess a dipole? In each case indicate which atom is delta+\delta+ and which is delta-\delta-. （b） 列出了您在有机化学中可能遇到的一些键。这些键中的哪些可能具有偶极子？在每种情况下都指示哪个原子是 delta+\delta+ ，哪个原子是 delta-\delta- 。
There are two stereoisomers of dichloroethene. The structure and shape of each molecule is: 二氯乙烯有两种立体异构体。每个分子的结构和形状为：
ClC=CCl
cis-dichloroethene 顺式二氯乙烯
ClC=CCl
trans-dichloroethene 反式二氯乙烯
Suggest why the cis isomer is polar, while the trans isomer is nonpolar. 说明为什么顺式异构体是极性的，而反式异构体是非极性的。
SUBJECT VOCABULARY 学科词汇
dipole exists when two charges of equal magnitude but opposite signs are separated by a small distance 当两个大小相等但符号相反的电荷相距很短时，就会出现偶极子
dipole moment the difference in magnitude between delta+\delta+ and delta\delta multiplied by the distance of separation between the charges 偶极矩 （Dipole moment） 电荷之间的 delta+\delta+ 大小差 和 delta\delta 乘以电荷之间的分离距离
LEARNING OBJECTIVES 学习目标
Understand that metals consist of giant lattices of metal ions (cations) in a sea of delocalised electrons.Know that metallic bonding is the strong electrostatic attraction between cations and the delocalised electrons.Be 电子。是 able to use the above two models to interpret simple properties of metals, e.g. electrical conductivity and high melting temperature.
EXAM HINT 考试提示
If asked to draw a diagram of a metallic bond in an exam, make sure you include a key showing ions and electrons. 如果在考试中被要求绘制金属键的图表，请确保包含一个显示离子和电子的键。
THE NATURE OF METALLIC BONDING 金属粘接的性质
Metals typically have the following physical properties: 金属通常具有以下物理特性：
high melting temperatures 高熔点
good electrical conductivity 良好的导电性
good thermal conductivity 良好的导热性
malleability 展性
ductility. 延性。
Any theory of the way that the atoms in a metal are bonded together must explain the above properties. 任何关于金属中原子键合方式的理论都必须解释上述性质。
Metals typically have one, two or three electrons in the outer shell of their atoms and have low ionisation energies. The electrical conductivity of a metal generally increases as the number of outer-shell electrons increases. 金属的原子外壳中通常有一个、两个或三个电子，并且具有低电离能。金属的电导率通常随着外层电子数量的增加而增加。
Since electrical conductivity depends on the presence of mobile carriers of electric charge, we can build a picture of a metal as consisting of an array of atoms with at least some of their outer-shell electrons removed and free to move throughout the structure. These delocalised electrons are largely responsible for the characteristic properties of metals. 由于电导率取决于移动电荷载体的存在，我们可以构建一个金属由原子阵列组成的图片，其中至少去除了一部分原子的外层电子，并且可以在整个结构中自由移动。这些离域电子在很大程度上是金属特性的原因。
fig A Diagram showing the particles present in a metal. 图 A 显示金属中存在的颗粒的图表。
The electrons are said to be delocalised since they are free to move throughout the structure and are not confined, i.e. localised, between any pair of cations. 电子被称为离域电子，因为它们可以在整个结构中自由移动，并且不受任何一对阳离子之间的限制，即局部化。
There are electrostatic forces of attraction between the cations and the delocalised electrons. This is known as metallic bonding. 阳离子和离域电子之间存在静电吸引力。这被称为金属键合。
EXPLAINING THE PHYSICAL PROPERTIES OF METALS 解释金属的物理性质
MELTING TEMPERATURE 熔融温度
In order to melt a metal, it is necessary to partially overcome the forces of attraction between the cations and the delocalised electrons to such an extent that the cations are free to move around the structure. Metals have a giant lattice structure where many of these forces must be overcome. The energy required to do this is usually very large, so the melting temperatures are typically high. 为了熔化金属，必须部分克服阳离子和离域电子之间的吸引力，使阳离子可以在结构周围自由移动。金属具有巨大的晶格结构，必须克服其中的许多力。这样做所需的能量通常非常大，因此熔化温度通常很高。
The number of delocalised electrons per cation plays a part in determining the melting temperature of a metal. 每个阳离子的离域电子数在决定金属的熔化温度方面起着一定的作用。
Group 1 metals have low melting temperatures. 第 1 类金属的熔化温度较低。
Group 2 metals have higher melting temperatures. 第 2 组金属具有较高的熔化温度。
Metals in the d-block typically have high melting temperatures because they have more delocalised electrons per cation. d 区中的金属通常具有较高的熔点温度，因为它们每个阳离子具有更多的离域电子。
Another factor that affects the melting temperature is the charge-to-radius ratio of the cation. The greater the charge-to-radius ratio, the stronger the attraction for the delocalised electrons. Therefore, for two cations of the same charge, the smaller cation will attract the delocalised electrons more strongly. This is why, for example, the melting temperature of lithium is greater than that of sodium. 影响熔解温度的另一个因素是阳离子的电荷-半径比。电荷-半径比越大，对离域电子的吸引力就越强。因此，对于相同电荷的两个阳离子，较小的阳离子将更强烈地吸引离域电子。这就是为什么锂的熔化温度高于钠的熔化温度。
ELECTRICAL CONDUCTIVITY 电导率
When a potential difference is applied across the ends of a metal, the delocalised electrons will be attracted to, and move towards, the positive terminal of the cell. This flow of electrons constitutes an electric current. 当在金属的末端施加电位差时，离域电子将被吸引并移向电池的正极端子。这种电子流构成电流。
THERMAL CONDUCTIVITY 导热
Two factors contribute to the ability of metals to transfer heat energy. 两个因素有助于金属传递热能的能力。
1 The free-moving delocalised electrons pass kinetic energy along the metal. 1 自由移动的离域电子沿金属传递动能。
2 The cations are closely packed and pass kinetic energy from one cation to another. 2 阳离子紧密堆积，并将动能从一个阳离子传递到另一个阳离子。
The conduction by the delocalised electrons is by far the more significant of the two factors. 离域电子的传导是迄今为止两个因素中更重要的一个。
MALLEABILITY AND DUCTILITY 延展性和延展性
Metals can be hammered or pressed into different shapes (malleability). They can also be drawn into a wire (ductility). Both of these properties depend on the ability of the delocalised electrons and the cations to move throughout the structure of the metal. 金属可以锤击或压制成不同的形状（延展性）。它们也可以拉成线材（延展性）。这两种特性都取决于离域电子和阳离子在整个金属结构中移动的能力。
When a stress is applied to a metal, the layers of cations may slide over one another (fig B). 当对金属施加应力时，阳离子层可能会相互滑动（图 B）。
fig B The effect of stress on a metal. 图 B 应力对金属的影响。
However, because the delocalised electrons are free moving, they move with the cations and prevent strong forces of repulsion forming between the cations in one layer and the cations in another layer. 然而，由于离域电子是自由移动的，它们会随阳离子一起移动，并防止在一层中的阳离子和另一层中的阳离子之间形成强大的排斥力。
CHECKPOINT 检查站
Explain what is meant by the term ‘metallic bonding’. 解释术语“金属粘合”的含义。
Suggest why the melting temperatures and electrical conductivities of sodium, magnesium and aluminium are in the order Na < Mg < Al\mathrm{Na}<\mathrm{Mg}<\mathrm{Al}. 说明为什么钠、镁和铝的熔化温度和电导率是有序 Na < Mg < Al\mathrm{Na}<\mathrm{Mg}<\mathrm{Al} 的。
SUBJECT VOCABULARY 学科词汇
delocalised electrons electrons that are not associated with any single atom or any single covalent bond metallic bonding the electrostatic force of attraction between the metal cations and delocalised electrons 离域电子 不与任何单个原子或任何单个共价键结合的电子 金属键合 金属阳离子和离域电子之间的静电吸引力
DID YOU KNOW? 您是否了解？
The argument relating charge-to-radius ratio of the cation to the melting temperature is oversimplified. The way the ions are arranged in the lattice also affects the melting temperature. This is why there is no regular trend in the melting temperatures of the Group 2 metals. The way in which the ions are arranged in the lattice changes down the group from beryllium to radium. This is not included in this book and is not required for IAS or IAL studies. 将阳离子的电荷-半径比与熔解温度联系起来的论点过于简单化。离子在晶格中的排列方式也会影响熔化温度。这就是为什么第 2 组金属的熔化温度没有规律的趋势。离子在晶格中的排列方式从铍到镭沿基团向下变化。这不包括在本书中，也不是 IAS 或 IAL 研究所必需的。
