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. In your IGCSE Science course, you need to know how protons, neutrons and electrons are arranged, and how this arrangement determines the properties and behaviour of elements in the periodic table.

理解原子结构是所有化学的基础。在IGCSE科学课程中，你需要知道质子、中子和电子是如何排列的，以及这种排列如何决定元素在周期表中的性质和行为。

1. The Atom | 原子

An atom is the smallest particle of an element that can exist and still retain the properties of that element. It consists of a central nucleus, containing protons and neutrons, surrounded by electrons moving in energy levels (shells).

原子是元素能存在并保留该元素性质的最小粒子。它由一个包含质子和中子的中心原子核，以及围绕核在能级（电子壳层）中运动的电子组成。

The nucleus is tiny and dense, while the electrons occupy a large volume of space around it. In a neutral atom, the number of protons equals the number of electrons.

原子核又小又密，而电子则占据核外广阔的空间。在电中性的原子中，质子数等于电子数。

2. Subatomic Particles | 亚原子粒子

There are three subatomic particles that you must know: protons, neutrons and electrons.

你必须了解三种亚原子粒子：质子、中子和电子。

Particle	Relative mass	Relative charge
Proton	1	+1
Neutron	1	0
Electron	1/1836	-1

The mass of an electron is so small that it is often taken as approximately zero. The charge on an electron is equal in size but opposite in sign to the charge on a proton.

电子的质量非常小，通常近似为零。电子所带的电荷与质子电荷大小相等、符号相反。

3. 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 of an atom. It defines which element the atom is. The mass number (A) is the total number of protons plus neutrons in the nucleus.

原子序数（Z）是原子核中的质子数，它决定了原子属于哪种元素。质量数（A）是原子核中质子数加中子数的总和。

Mass number = number of protons + number of neutrons

For example, a carbon atom with 6 protons and 6 neutrons has an atomic number of 6 and a mass number of 12.

例如，一个含有6个质子和6个中子的碳原子，其原子序数为6，质量数为12。

4. Electron Configuration | 电子排布

Electrons occupy energy levels (shells) around the nucleus. The first shell can hold a maximum of 2 electrons, and the second and third shells can hold a maximum of 8 electrons each. For IGCSE, you only need to consider the first three shells.

电子占据原子核周围的能级（壳层）。第一层最多容纳2个电子，第二层和第三层最多各容纳8个电子。在IGCSE中，你只需要考虑前三层。

The electron configuration is written by showing the number of electrons in each shell, separated by commas. For example, sodium (Na) has 11 electrons, so its configuration is 2,8,1.

电子排布通过依次写出每层电子数（用逗号隔开）来表示。例如，钠（Na）有11个电子，其排布为2,8,1。

Electron configurations are usually shown in diagrams with circles and crosses, but the written form is just as important. You must be able to draw the configuration for the first 20 elements.

电子排布通常用圆圈和叉号的图表示，但书面形式同样重要。你必须能画出前20号元素的电子排布图。

5. Electronic Structure and the Periodic Table | 电子结构与周期表

In the periodic table, elements are arranged in order of increasing atomic number. Elements in the same group (vertical column) have the same number of outer-shell electrons, which gives them similar chemical properties.

在周期表中，元素按原子序数递增排列。同一族（纵列）的元素具有相同的最外层电子数，因此化学性质相似。

Group I elements have 1 electron in their outer shell.
Group II elements have 2 electrons in their outer shell.
Group VII elements have 7 electrons in their outer shell.
Group 0 elements have 8 electrons in their outer shell (except helium, which has 2).

第一族元素最外层有1个电子。

第二族元素最外层有2个电子。

第七族元素最外层有7个电子。

第0族元素最外层有8个电子（氦例外，只有2个）。

The number of occupied shells corresponds to the period (horizontal row) in which the element is located.

占据的电子层数对应元素所在的周期（横行）。

6. Isotopes | 同位素

Isotopes are atoms of the same element which have the same number of protons but a different number of neutrons. This means they have the same atomic number but different mass numbers.

同位素是同一种元素的原子，具有相同的质子数但中子数不同。这意味着它们的原子序数相同、质量数不同。

For example, chlorine-35 and chlorine-37 both have 17 protons, but chlorine-35 has 18 neutrons while chlorine-37 has 20 neutrons.

例如，氯-35和氯-37都有17个质子，但氯-35有18个中子，氯-37有20个中子。

Isotopes of the same element have identical chemical properties because chemical behaviour depends on the number of electrons, which is the same. However, their physical properties may differ slightly, such as density or rate of diffusion.

同一元素的同位素具有完全相同的化学性质，因为化学行为取决于电子数，而电子数相同。但它们的物理性质可能略有差异，如密度或扩散速率。

Relative atomic mass is the weighted mean mass of all the naturally occurring isotopes of an element compared to 1/12 of the mass of carbon-12.

相对原子质量是元素所有天然同位素的加权平均质量，与碳-12质量的1/12相比较。

7. Ions | 离子

Ions are charged particles formed when atoms gain or lose electrons. When an atom loses electrons, it becomes a positively charged cation. When it gains electrons, it becomes a negatively charged anion.

离子是原子获得或失去电子后形成的带电粒子。当原子失去电子时，它成为带正电荷的阳离子；当它获得电子时，它成为带负电荷的阴离子。

For example, a sodium atom (Na) loses one electron to form a Na⁺ ion. A chlorine atom (Cl) gains one electron to form a Cl⁻ ion.

例如，钠原子（Na）失去1个电子形成Na⁺离子；氯原子（Cl）获得1个电子形成Cl⁻离子。

Ionic charges are determined by the group number. Group I metals form +1 ions, Group II metals form +2 ions, Group VI non-metals form −2 ions, and Group VII non-metals form −1 ions.

离子电荷由族序数决定。第一族金属形成+1离子，第二族金属形成+2离子，第六族非金属形成−2离子，第七族非金属形成−1离子。

8. Relative Atomic Mass Calculations | 相对原子质量计算

You may be asked to calculate the relative atomic mass (Aᵣ) of an element given the mass numbers and abundances of its isotopes. The formula is:

你可能需要根据同位素的质量数和丰度计算元素的相对原子质量（Aᵣ）。公式为：

Aᵣ = (mass₁ × abundance₁ + mass₂ × abundance₂ + …) ÷ total abundance

For example, chlorine has 75% of carbon-35 and 25% of carbon-37. The relative atomic mass is:

例如，氯有75%的碳-35和25%的碳-37，其相对原子质量为：

(35 × 75 + 37 × 25) ÷ 100 = (2625 + 925) ÷ 100 = 3550 ÷ 100 = 35.5

So the relative atomic mass of chlorine is 35.5, which is why chlorine appears as 35.5 on the periodic table.

因此，氯的相对原子质量为35.5，这就是为什么周期表中氯显示为35.5。

9. Understanding the Periodic Table Layout | 理解周期表布局

The periodic table is divided into periods (horizontal rows) and groups (vertical columns). Elements in the same group have similar chemical properties. Metals are found on the left and in the middle, while non-metals are on the right. The zig-zag line separates metals from non-metals.

周期表分为周期（横行）和族（纵列）。同一族元素化学性质相似。金属位于左侧和中部，非金属位于右侧。锯齿线将金属与非金属分开。

Group 0 (noble gases) are unreactive because they have a full outer shell of electrons. This full shell gives them a stable electronic configuration.

第0族（稀有气体）不活泼，因为它们具有满电子外层。这个满壳层使它们具有稳定的电子构型。

Group I elements (alkali metals) are soft, have low density and are very reactive. Their reactivity increases as you go down the group because the outer electron is further from the nucleus and is more easily lost.

第一族元素（碱金属）柔软、密度低且非常活泼。随着向下移动，反应性增加，因为外层电子离核更远，更容易失去。

Group VII elements (halogens) are non-metals that exist as diatomic molecules. Their reactivity decreases as you go down the group because the atoms get larger and it becomes harder to gain an electron.

第七族元素（卤素）是非金属，以双原子分子存在。随着向下移动反应性降低，因为原子变大，获得电子变得更困难。

10. Common Exam Tips | 常见考试提示

In the exam, make sure you can:

在考试中，确保你能：

State the charge and relative mass of each subatomic particle.
Calculate the number of protons, neutrons and electrons from atomic and mass numbers.
Write and draw electron configurations for the first 20 elements.
Define isotope, ion, atomic number and mass number.
Calculate relative atomic mass from isotope abundance data.
Explain trends in groups I and VII using electron structure.

说出每种亚原子粒子的电荷和相对质量。

从原子序数和质量数计算质子、中子和电子的数目。

书写并画出前20号元素的电子排布。

定义同位素、离子、原子序数和质量数。

根据同位素丰度数据计算相对原子质量。

用电子结构解释第一族和第七族的趋势。

Be careful with the spelling of “neutron” and “electron” – it is a common mistake to reverse the letters. Also remember that in a neutral atom, the number of electrons equals the number of protons only; the neutrons are not involved in balancing charge.

注意“neutron”和“electron”的拼写——把字母顺序写反是常见错误。还要记住，在电中性原子中，电子数只等于质子数；中子不参与电荷平衡。

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