📚 Edexcel IGCSE Science: Atomic Structure and the Periodic Table | Edexcel IGCSE 科学：原子结构与元素周期表
This revision guide focuses on atomic structure and the periodic table, a fundamental topic in the Edexcel IGCSE Science specification. You will learn about the particles that make up atoms, how to calculate relative atomic mass, and how elements are arranged in the periodic table. Understanding these ideas is essential for success in both chemistry and combined science exams.
本复习指南聚焦于原子结构与元素周期表，这是爱德思 IGCSE 科学课程中的一个基础主题。你将学习构成原子的粒子、如何计算相对原子质量，以及元素在周期表中的排列方式。理解这些概念对于化学和综合科学考试的成功至关重要。
1. The Atom | 1. 原子
All matter is made of atoms. An atom is the smallest particle of an element that can take part in a chemical reaction. Atoms are extremely small, about 1 × 10⁻¹⁰ m in diameter. They contain even smaller subatomic particles: protons, neutrons and electrons. The protons and neutrons are located in a dense central nucleus, while the electrons move around the nucleus in energy levels (shells).
所有物质都由原子组成。原子是元素能参与化学反应的最小粒子。原子非常小，直径约为 1 × 10⁻¹⁰ 米。原子包含更小的亚原子粒子：质子、中子和电子。质子和中子位于致密的原子核中，而电子在核外的能层（壳层）中运动。
2. Subatomic Particles | 2. 亚原子粒子
The three subatomic particles have different relative masses and charges. Protons have a relative mass of 1 and a relative charge of +1. Neutrons have a relative mass of 1 and a relative charge of 0. Electrons have a relative mass of 1/1840 (often taken as 0) and a relative charge of -1. The properties are summarised in the table below.
三种亚原子粒子具有不同的相对质量和相对电荷。质子的相对质量为 1，相对电荷为 +1。中子的相对质量为 1，相对电荷为 0。电子的相对质量约为 1/1840（通常近似为 0），相对电荷为 -1。这些性质总结在下表中。
| Particle | Relative mass | Relative charge |
| Proton | 1 | +1 |
| Neutron | 1 | 0 |
| Electron | 1/1840 (≈0) | -1 |
An atom is electrically neutral because the number of protons equals the number of electrons. The positive charges cancel the negative charges exactly.
原子是电中性的，因为质子数等于电子数。正电荷恰好抵消负电荷。
3. Atomic Number and Mass Number | 3. 原子序数与质量数
The atomic number (Z) is the number of protons in the nucleus of an atom. In a neutral atom, the number of electrons equals the number of protons. The mass number (A) is the total number of protons and neutrons in the nucleus. You can calculate the number of neutrons using the formula below.
原子序数（Z）是原子核中的质子数。在中性原子中，电子数等于质子数。质量数（A）是原子核中质子与中子的总数。你可以用下面的公式计算中子数。
neutron number = mass number – atomic number
For example, a sodium atom has an atomic number of 11 and a mass number of 23. Therefore it has 11 protons, 11 electrons, and 12 neutrons. Check that 23 – 11 = 12.
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 个电子和 12 个中子。验证：23 – 11 = 12。
4. Isotopes | 4. 同位素
Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. This means they have the same atomic number but different mass numbers. For example, chlorine-35 and chlorine-37 are two isotopes of chlorine. Chlorine-35 has 17 protons and 18 neutrons, while chlorine-37 has 17 protons and 20 neutrons.
同位素是同一元素的不同原子，它们具有相同的质子数但不同的中子数。这意味着它们具有相同的原子序数但不同的质量数。例如，氯-35 和氯-37 是氯的两种同位素。氯-35 有 17 个质子和 18 个中子，而氯-37 有 17 个质子和 20 个中子。
Isotopes have the same chemical properties because they have the same electronic configuration, but their physical properties may differ. For example, an isotope with a larger mass may have a higher boiling point or diffuse more slowly.
同位素具有相同的化学性质，因为它们具有相同的电子排布，但物理性质可能不同。例如，质量更大的同位素可能沸点更高或扩散更慢。
5. Electronic Configuration | 5. 电子排布
Electrons are arranged in energy levels (shells) around the nucleus. The arrangement of electrons is called the electronic configuration. The first shell can hold up to 2 electrons, the second and third shells can hold up to 8 electrons each.
电子在原子核周围的能层（壳层）中排列。电子的排列方式称为电子排布。第一个能层最多容纳 2 个电子，第二和第三能层最多各容纳 8 个电子。
To write the electronic configuration, you fill the shells in order. For example, carbon has 6 electrons, so its electronic configuration is 2, 4. Sodium has 11 electrons, so it is 2, 8, 1. Sulfur has 16 electrons, so it is 2, 8, 6.
写电子排布时，按顺序填充能层。例如，碳有 6 个电子，所以它的电子排布是 2, 4。钠有 11 个电子，所以是 2, 8, 1。硫有 16 个电子，所以是 2, 8, 6。
6. The Periodic Table | 6. 元素周期表
The periodic table arranges elements in order of increasing atomic number. Each element is represented by a box showing its symbol, atomic number and mass number. The table has rows called periods and columns called groups.
元素周期表按原子序数递增的顺序排列元素。每个元素由一个方框表示，方框内显示符号、原子序数和质量数。周期表有行称为周期，列称为族。
Elements in the same group have the same number of outer-shell electrons and therefore similar chemical properties. The modern periodic table is based on Mendeleev’s original table, but elements are now arranged by atomic number instead of atomic mass.
同一族的元素具有相同的外层电子数，因此化学性质相似。现代周期表基于门捷列夫的原始表，但现在按原子序数而非原子量排列元素。
7. Groups and Periods | 7. 族与周期
A period is a horizontal row. The period number indicates the number of occupied electron shells. For example, elements in the second period have two electron shells. A group is a vertical column.
周期是横排。周期号表示已占据的电子能层数。例如，第二周期的元素有 2 个电子壳层。族是纵列。
The group number (for groups 1, 2 and 13-18) is related to the number of outer-shell electrons. For example, group 1 elements have 1 outer-shell electron, and group 7 elements have 7 outer-shell electrons. Knowing the group number helps you predict the reactivity and the formulas of compounds.
族号（对于第 1、2 和 13-18 族）与最外层电子数有关。例如，第 1 族元素有 1 个最外层电子，第 7 族元素有 7 个最外层电子。知道族号有助于预测反应活性和化合物化学式。
8. Group 1 Alkali Metals | 8. 第 1 族碱金属
Group 1 elements, also called alkali metals, are highly reactive metals. They have one outer-shell electron, which they lose easily to form a positive ion with a charge of +1. Their reactivity increases down the group, because the outer electron is farther from the nucleus and is more easily lost.
第 1 族元素也称为碱金属，是高度活泼
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