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 why elements behave the way they do, how they bond, and why the periodic table is arranged as it is. In this revision article, we will break down the key ideas you need for your Edexcel IGCSE Science exam.

理解原子结构是所有化学的基础。它解释了元素为何具有这样的性质、它们如何成键，以及元素周期表为何如此排列。在这篇复习文章中，我们将拆解 Edexcel IGCSE 科学考试所需的关键概念。

1. The Atom and its Subatomic Particles | 原子及其亚原子粒子

Every atom is made of three fundamental particles: protons, neutrons and electrons. Protons have a positive charge, neutrons have no charge, and electrons have a negative charge. Protons and neutrons are found in the tiny nucleus, while electrons orbit in shells around the nucleus.

每个原子都由三种基本粒子组成：质子、中子和电子。质子带正电，中子不带电，电子带负电。质子和中子位于微小的原子核中，而电子在原子核周围的壳层中运动。

The relative mass and charge of each particle are essential to remember:

每种粒子的相对质量和电荷是必须记住的：

Particle	Relative Mass	Relative Charge
Proton	1	+1
Neutron	1	0
Electron	1/1840 (almost 0)	−1

An atom is neutral overall because the number of protons equals the number of electrons.

原子整体呈电中性，因为质子数等于电子数。

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

The atomic number (Z) is the number of protons in the nucleus. It defines the element. The mass number (A) is the total number of protons plus neutrons.

原子序数（Z）是原子核中的质子数。它定义了元素种类。质量数（A）是质子数加中子数的总和。

mass number = number of protons + number of neutrons

For example, a sodium atom has atomic number 11 and mass number 23. It therefore has 11 protons, 11 electrons and 23 − 11 = 12 neutrons.

例如，钠原子的原子序数为 11，质量数为 23。因此它有 11 个质子、11 个电子，以及 23 − 11 = 12 个中子。

You can write this notation: ²³₁₁Na. The top number is the mass number, and the bottom number is the atomic number.

可以这样写：²³₁₁Na。上面的数字是质量数，下面的数字是原子序数。

3. Isotopes | 同位素

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

同位素是同一元素的原子，它们具有相同数目的质子，但中子数目不同。因此它们的原子序数相同，但质量数不同。

For example, carbon-12 (¹²C) and carbon-14 (¹⁴C) are both carbon isotopes. Carbon-12 has 6 neutrons, while carbon-14 has 8 neutrons.

例如，碳-12（¹²C）和碳-14（¹⁴C）都是碳的同位素。碳-12 有 6 个中子，而碳-14 有 8 个中子。

Isotopes of the same element have identical chemical properties because chemical behaviour depends on the number of electrons, not the number of neutrons. However, physical properties such as mass may differ.

同一元素的同位素具有相同的化学性质，因为化学行为取决于电子数目，而不是中子数目。然而，质量等物理性质可能不同。

4. Electron Shells and Electronic Configuration | 电子壳层与电子排布

Electrons occupy energy levels (shells) around the nucleus. The first shell can hold up to 2 electrons, the second shell can hold up to 8, and the third shell can hold up to 8 (for the first 20 elements).

电子占据原子核周围的能级（壳层）。第一壳层最多容纳 2 个电子，第二壳层最多容纳 8 个，第三壳层最多容纳 8 个（对于前 20 号元素）。

To work out the electronic configuration, fill the shells in order from the inside out. For example:

要确定电子排布，按从内到外的顺序填充壳层。例如：

Oxygen (8): 2, 6

氧（8）：2, 6
Sodium (11): 2, 8, 1

钠（11）：2, 8, 1
Chlorine (17): 2, 8, 7

氯（17）：2, 8, 7

The electrons in the outermost shell are called valence electrons. They determine how the atom reacts.

最外层壳层中的电子称为价电子。它们决定原子如何反应。

5. The Periodic Table – Groups and Periods | 元素周期表——族和周期

The periodic table arranges elements in order of increasing atomic number. Each row is called a period, and each column is called a group.

元素周期表按原子序数递增的顺序排列元素。每一行称为一个周期，每一列称为一个族。

Elements in the same group have the same number of electrons in their outer shell. This gives them similar chemical properties. For example, Group 1 elements all have 1 outer electron, and Group 7 elements all have 7 outer electrons.

同一族的元素具有相同的最外层电子数。这使得它们具有相似的化学性质。例如，第 1 族元素都有 1 个外层电子，第 7 族元素都有 7 个外层电子。

The number of shells increases as you go down a group, and the number of outer electrons increases as you go across a period.

在族中向下移动时，壳层数目增加；在周期中向右移动时，外层电子数目增加。

6. Group 1 – Alkali Metals | 第 1 族——碱金属

Group 1 elements (litium, sodium, potassium, etc.) are soft metals that react rapidly with water to form an alkaline solution and hydrogen gas. Their reactivity increases down the group because the outer electron is further from the nucleus and is more easily lost.

第 1 族元素（锂、钠、钾等）是软金属，它们与水迅速反应生成碱性溶液和氢气。它们的反应活性随族向下而增强，因为外层电子距离原子核更远，更容易失去。

2Na + 2H₂O → 2NaOH + H₂

Sodium fizzes, moves on the water surface, and may melt into a ball. Potassium burns with a lilac flame.

钠浮在水面上嘶嘶作响、四处移动，并可能熔成小球。钾燃烧时产生淡紫色火焰。

7. Group 7 – Halogens | 第 7 族——卤素

Group 7 elements (fluorine, chlorine, bromine, iodine) are non-metals with 7 outer electrons. They react by gaining one electron to form negative ions (halides) with a charge of −1.

第 7 族元素（氟、氯、溴、碘）是非金属，具有 7 个外层电子。它们通过获得一个电子形成带 −1 电荷的负离子（卤化物）。

Reactivity decreases down the group. Fluorine is the most reactive, while iodine is the least. A more reactive halogen can displace a less reactive halogen from its salt solution.

反应活性在族中向下递减。氟的反应活性最强，碘最弱。较活泼的卤素能从其盐溶液中置换出较不活泼的卤素。

Cl₂ + 2KBr → 2KCl + Br₂

Chlorine displaces bromine because chlorine is above bromine in Group 7.

氯能置换出溴，因为在第 7 族中氯位于溴的上方。

8. Group 0 – Noble Gases | 第 0 族——稀有气体

Group 0 elements (helium, neon, argon, krypton, xenon) have a full outer shell of electrons. Helium has 2, and the rest have 8. This makes them stable and unreactive.

第 0 族元素（氦、氖、氩、氪、氙）具有充满电子的外壳层。氦有 2 个电子，其余有 8 个。这使得它们稳定且不反应。

Noble gases are monatomic (exist as single atoms) and are used in contexts where unreactive gases are needed. Argon is used in welding to prevent oxidation, and neon is used in advertising signs.

稀有气体是单原子的（以单个原子存在），用于需要不反应气体的场合。氩气用于焊接以防止氧化，氖气用于广告灯管。

As you go down Group 0, the boiling point increases because the atoms have greater mass and stronger intermolecular forces, even though they remain unreactive.

在稀有气体族中向下移动时，沸点升高，因为原子质量更大，分子间作用力更强，尽管它们仍不反应。

9. Metals and Non-Metals | 金属与非金属

The periodic table can be divided into metals and non-metals. Metals are found on the left and centre of the table, while non-metals are on the right. Metals tend to lose electrons to form positive ions, while non-metals gain electrons to form negative ions.

元素周期表可分为金属和非金属。金属位于表格的左侧和中间，非金属位于右侧。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。

Typical metal properties include high electrical conductivity, high melting points, malleability and metallic lustre. Non-metals are usually poor conductors, brittle in the solid state, and have lower melting points.

金属的典型性质包括高导电性、高熔点、延展性和金属光泽。非金属通常导电性差，固态时脆弱，熔点较低。

Some elements, such as carbon (graphite), show non-metal properties but also conduct electricity due to delocalised electrons.

有些元素，如碳（石墨），显示非金属的性质，但也因离域电子而导电。

10. Patterns and Predicting Properties | 规律与预测性质

The periodic table is a powerful prediction tool. If you know an element’s group and period, you can predict its electronic configuration, ion charge and reactivity trends.

元素周期表是一个强大的预测工具。如果你知道元素的族和周期，就可以预测其电子排布、离子电荷和反应活性趋势。

Elements in Group 2 tend to form +2 ions.

第 2 族元素倾向于形成 +2 离子。
Elements in Group 6 tend to form −2 ions.

第 6 族元素倾向于形成 −2 离子。
Elements in Period 3 have 3 occupied shells.

第 3 周期元素有 3 个被占据的壳层。

For example, magnesium (Group 2, Period 3) has electronic configuration 2,8,2 and forms Mg²⁺ ions in reactions.

例如，镁（第 2 族，第 3 周期）的电子排布为 2,8,2，在反应中形成 Mg²⁺ 离子。

Exam tip: Always link electronic configuration to group number and period number. The group number tells you the outer electrons, and the period number tells you the number of shells.

考试提示：始终将电子排布与族号和周期号联系起来。族号告诉你外层电子数，周期号告诉你壳层数。

11. Historical Development of the Periodic Table | 元素周期表的历史发展

Dmitri Mendeleev arranged the elements by increasing atomic weight and placed elements with similar properties in columns. He left gaps for undiscovered elements and even predicted their properties. Later, the table was reordered by atomic number when Henry Moseley showed that this was the true basis of periodicity.

德米特里·门捷列夫按原子量递增排列元素，并将性质相似的元素放在同一列中。他为未发现的元素留出空位，甚至预测了它们的性质。后来，亨利·莫塞莱表明原子序数才是周期性的真正基础，表格被重新排列。

Modern periodic law states that the properties of elements are a periodic function of their atomic number. This explains why isotopes of the same element occupy the same position in the table.

现代周期律指出，元素的性质是其原子序数的周期函数。这解释了为什么同一元素的同位素在周期表中占据相同的位置。

12. Worked Exam Question | 典型考试题解析

Question: An element X has atomic number 19 and mass number 39. Give the number of protons, neutrons and electrons, and write its electronic configuration.

题目：某元素 X 的原子序数为 19，质量数为 39。写出它的质子数、中子数和电子数，并写出其电子排布。

Protons = 19 (atomic number). Electrons = 19 (neutral atom). Neutrons = 39 − 19 = 20. Electronic configuration: 2,8,8,1.

质子数 = 19（原子序数）。电子数 = 19（中性原子）。中子数 = 39 − 19 = 20。电子排布：2,8,8,1。

Since the outer shell has 1 electron, element X belongs to Group 1. It has 4 shells, so it is in Period 4. This element is potassium.

由于最外层有 1 个电子，元素 X 属于第 1 族。它有 4 个壳层，因此位于第 4 周期。该元素是钾。

Always show your working for such calculations. Even if the final answer is wrong, you can gain method marks.

对于此类计算，务必写出过程。即使最终答案错误，你也可以获得方法分。

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