Atomic Structure and the Periodic Table | 原子结构与元素周期表

📚 Atomic Structure and the Periodic Table | 原子结构与元素周期表

Understanding atomic structure is the foundation of all chemistry. It explains how atoms are built, how elements behave, and why the periodic table is arranged in its familiar form.

理解原子结构是所有化学的基础。它解释了原子如何构成、元素如何表现，以及元素周期表为什么以我们熟悉的形式排列。

1. The Structure of an Atom | 原子的结构

An atom is the smallest particle of an element that can take part in a chemical reaction. It contains a central nucleus surrounded by electrons. The nucleus is very small and dense compared with the whole atom, and it is positively charged.

原子是元素中能够参与化学反应的最小粒子。它由中心原子核以及围绕在核外的电子组成。与整个原子相比，原子核非常小且密度很大，并且带正电荷。

The nucleus is made of protons and neutrons, which are together called nucleons. Electrons move around the nucleus in energy levels (shells) and are negatively charged.

原子核由质子和中子构成，二者统称为核子。电子在原子核周围的能层（即电子壳层）中运动，带负电荷。

2. Subatomic Particles | 亚原子粒子

All atoms are made from three types of subatomic particle: protons, neutrons and electrons. Their relative masses and relative charges are given in the table below.

所有原子都由三种亚原子粒子组成：质子、中子和电子。它们的相对质量和相对电荷如下表所示。

Particle	Relative mass	Relative charge
Proton	1	+1
Neutron	1	0
Electron	1/1840	-1

Because an atom has no overall charge, the number of protons is always equal to the number of electrons in a neutral atom.

由于原子整体不带电，中性原子中质子的数目始终等于电子的数目。

3. Atomic Number and Mass Number | 原子序数与质量数

The atomic number (Z) is the number of protons in an atom. It defines the element. The mass number (A) is the total number of protons and neutrons in an atom.

原子序数（Z）是原子中质子的数目，它决定了元素的种类。质量数（A）是原子中质子数和中子数的总和。

mass number = number of protons + number of neutrons

质量数 = 质子数 + 中子数

For example, an oxygen atom has atomic number 8 and mass number 16. It therefore contains 8 protons, 8 neutrons and 8 electrons.

例如，氧原子原子序数为8、质量数为16，因此含有8个质子、8个中子和8个电子。

4. Isotopes | 同位素

Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. They therefore have the same atomic number but different mass numbers.

同位素是同一元素中具有相同质子数但不同中子数的原子，因此它们具有相同的原子序数，但质量数不同。

Carbon-12 (¹²C) has 6 protons and 6 neutrons. Carbon-14 (¹⁴C) also has 6 protons but has 8 neutrons. Both are carbon isotopes.

碳-12（¹²C）含有6个质子和6个中子；碳-14（¹⁴C）同样有6个质子，但有8个中子。两者都是碳的同位素。

Isotopes of an element have the same chemical properties because they have the same number of electrons and the same electron arrangement. They may have different physical properties, such as mass or density.

同一元素的同位素具有相同的化学性质，因为它们具有相同的电子数和相同的电子排布。它们的物理性质可能不同，例如质量或密度。

5. Electron Arrangement | 电子排布

Electrons are arranged in shells (energy levels) around the nucleus. For the first 20 elements, the rules are simple: the first shell can hold up to 2 electrons, the second shell can hold up to 8 electrons, and the third shell can hold up to 8 electrons before the fourth shell begins to fill.

电子围绕原子核排列在电子壳层（能层）中。对于前20号元素，规律很简单：第一个壳层最多容纳2个电子，第二个壳层最多容纳8个电子，第三个壳层最多容纳8个电子，然后才填充第四个壳层。

For example, sodium has 11 electrons. Its electron arrangement is 2, 8, 1, meaning that it has 2 electrons in the first shell, 8 in the second shell and 1 in the outer shell.

例如，钠有11个电子，其电子排布为2，8，1，意思是第一个壳层有2个电子，第二个壳层有8个电子，最外层有1个电子。

The number of electrons in the outer shell determines how an atom reacts chemically.

最外层的电子数决定了一个原子如何发生化学反应。

6. The Periodic Table Layout | 元素周期表的布局

The periodic table arranges all known elements in order of increasing atomic number. Each horizontal row is called a period. Each vertical column is called a group.

元素周期表将所有已知元素按原子序数递增的顺序排列。每个横排称为一个周期，每个纵列称为一个族。

In the Edexcel IGCSE specification, groups are numbered 1 to 7 and 0. Group 1 contains the alkali metals, Group 2 contains the alkaline earth metals, Group 7 contains the halogens and Group 0 contains the noble gases.

在Edexcel IGCSE大纲中，族编号为1到7和0。第1族是碱金属，第2族是碱土金属，第7族是卤素，第0族是稀有气体。

Elements in the same group have the same number of outer-shell electrons. For groups 1 and 2, this is the same as the group number. For group 7, there are 7 outer-shell electrons; for group 0, there are 8 (except helium, which has 2).

同一族的元素具有相同的最外层电子数。对于第1族和第2族，最外层电子数等于族号。第7族有7个最外层电子；第0族有8个（但氦除外，它有2个）。

7. Groups and Periods | 族与周期

Elements in the same group have similar chemical properties because they have the same number of outer-shell electrons. As you go down a group, the number of occupied electron shells increases, and the atoms become larger.

同一族元素具有相似的化学性质，因为它们具有相同的最外层电子数。随着族从上到下移动，电子壳层增多，原子变大。

Elements in the same period have the same number of electron shells. As you move across a period from left to right, the atomic number increases and the number of outer-shell electrons increases by one each time.

同一周期元素具有相同的电子壳层数。在周期中从左向右移动时，原子序数增大，最外层电子数每次增加1个。

Knowing the group number and period number allows you to write the electron arrangement. For example, magnesium is in Group 2 and Period 3, so it has 3 shells and 2 outer electrons: 2, 8, 2.

知道族号和周期数就可以写出电子排布。例如，镁位于第2族、第3周期，因此它有3个壳层和2个最外层电子：2，8，2。

8. Metals and Non-metals | 金属与非金属

On the periodic table, metals are found on the left side and in the middle, while non-metals are found on the right side. A stepped line separates them.

在元素周期表中，金属位于左侧和中部，非金属位于右侧。两者之间有一条阶梯线分界。

Metals are generally shiny, malleable and good conductors of heat and electricity. Non-metals are usually dull, brittle and poor conductors (except graphite).

金属通常有光泽、具有延展性，是良好的热和电导体。非金属通常暗淡、易碎，并且导电导热性差（石墨除外）。

When elements react, metals tend to lose electrons to form positive ions, while non-metals tend to gain electrons to form negative ions.

当元素发生反应时，金属倾向于失去电子形成正离子，而非金属倾向于获得电子形成负离子。

9. Group 1: Alkali Metals | 第1族：碱金属

The alkali metals are lithium, sodium, potassium, rubidium, caesium and francium. They are soft, have relatively low densities, and cut easily with a knife.

碱金属包括锂、钠、钾、铷、铯和钫。它们质软、密度相对较小，容易用小刀切开。

They react vigorously with water to produce hydrogen gas and an alkaline hydroxide solution. For example:

它们能与水剧烈反应，产生氢气和碱性氢氧化物溶液。例如：

2Na + 2H₂O → 2NaOH + H₂

Reactivity increases going down Group 1, because the outer electron is further from the nucleus and is more easily lost.

沿着第1族向下，反应性增强，因为最外层电子离核更远，更容易失去。

10. Group 7: Halogens | 第7族：卤素

The halogens are fluorine, chlorine, bromine, iodine and astatine. They are non-metals and exist as diatomic molecules, such as F₂, Cl₂, Br₂ and I₂.

卤素包括氟、氯、溴、碘和砹。它们是非金属，以双原子分子存在，例如F₂、Cl₂、Br₂和I₂。

At room temperature, chlorine is a pale green gas, bromine is a reddish-brown liquid, and iodine is a grey-black solid. Their melting and boiling points increase going down the group.

在室温下，氯是黄绿色气体，溴是红棕色液体，碘是灰黑色固体。沿着第7族向下，熔点和沸点升高。

Reactivity decreases going down Group 7, because the incoming electron is added further from the nucleus and is less strongly attracted.

沿着第7族向下，反应性减弱，因为新加入的电子离核更远，受到的吸引力更弱。

11. Group 0: Noble Gases | 第0族：稀有气体

The noble gases are helium, neon, argon, krypton, xenon and radon. They are colourless gases and are very unreactive because they have a full outer shell of electrons.

稀有气体包括氦、氖、氩、氪、氙和氡。它们是无色气体，由于具有满电子的最外层壳层，因此非常不活泼。

A full outer shell makes the atom stable, so noble gases do not easily form bonds or ions. This is why they are sometimes called inert gases.

满的最外层使原子稳定，因此稀有气体不容易成键或形成离子，因此有时也称为惰性气体。

Helium has 2 outer electrons, but this fills its only shell. The other noble gases have 8 outer electrons.

氦有2个最外层电子，但这已经填满它唯一的壳层。其他稀有气体都有8个最外层电子。

12. Predicting Properties and Exam Tips | 预测性质与考试建议

You can use the periodic table to predict the electron arrangement of an element. The period number tells you the number of shells; the group number tells you the number of outer electrons.

你可以利用元素周期表预测元素的电子排布。周期数告诉你电子壳层数，族号告诉你最外层电子数。

For example, an element with atomic number 12 and mass number 24 has 12 protons, 12 electrons and 12 neutrons. Its electron arrangement is 2, 8, 2, so it is in Period 3 and Group 2.

例如，原子序数为12、质量数为24的元素，有12个质子、12个电子和12个中子。它的电子排布是2，8，2，所以位于第3周期、第2族。

In exams, always state the number of protons and electrons separately. Remember that the atomic number is not given as a symbol; you must read it directly from the periodic table.

考试中，务必分开说明质子和电子的数目。记住原子序数不是符号给出的，而是直接从周期表中读出的。

Practice writing electron arrangements for elements 1 to 20 until you can do this quickly and accurately. Also practise explaining trends in reactivity using the distance of the outer electrons from the nucleus.

反复练习书写前20号元素的电子排布，直到快速又准确。同时练习用最外层电子与原子核的距离来解释反应性变化的趋势。

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Atomic Structure and the Periodic Table | 原子结构与元素周期表