Atomic Structure | 原子结构

📚 Atomic Structure | 原子结构

Atoms are the fundamental building blocks of matter. Understanding their structure is essential for explaining the properties of elements, compounds, and reactions in GCSE Science.

原子是物质的基本组成单位。理解原子结构是解释元素、化合物和反应性质的关键，也是GCSE科学的核心内容。

1. Subatomic Particles | 亚原子粒子

The atom is composed of three main subatomic particles: protons, neutrons, and electrons. Protons carry a positive charge, neutrons are neutral, and electrons carry a negative charge.

原子由三种主要的亚原子粒子构成：质子、中子和电子。质子带正电荷，中子不带电，电子带负电荷。

Proton – relative charge +1, relative mass 1, located in the nucleus.
Neutron – relative charge 0, relative mass 1, located in the nucleus.
Electron – relative charge -1, relative mass 1/1836 (approximately negligible), located in shells around the nucleus.

质子 – 相对电荷 +1，相对质量 1，位于原子核内。
中子 – 相对电荷 0，相对质量 1，位于原子核内。
电子 – 相对电荷 -1，相对质量约为 1/1836（可忽略不计），位于原子核外的电子壳层中。

Proton mass = 1.67 × 10⁻²⁷ kg

质子质量 = 1.67 × 10⁻²⁷ kg

The number of protons determines which element an atom belongs to. In a neutral atom, the number of electrons equals the number of protons.

质子数决定了原子属于哪种元素。在电中性原子中，电子数等于质子数。

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. The mass number (A) is the total number of protons and neutrons in the nucleus.

原子序数（Z）是指原子核中的质子数。质量数（A）是指原子核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

This can be written using nuclide notation:

这可以用核素符号表示：

ᴬ₉X (where A is the mass number, Z is the atomic number, and X is the element symbol)

ᴬ₉X（其中 A 为质量数，Z 为原子序数，X 为元素符号）

For example, sodium has atomic number 11 and mass number 23, so it contains 11 protons, 11 electrons, and 12 neutrons.

例如，钠的原子序数为 11，质量数为 23，因此它含有 11 个质子、11 个电子和 12 个中子。

3. Isotopes | 同位素

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

同位素是指同一种元素中具有相同质子数但中子数不同的原子。因此它们的原子序数相同，但质量数不同。

Examples of isotopes include carbon-12 and carbon-14:

同位素的例子包括碳-12 和碳-14：

Isotope	Protons	Neutrons
Carbon-12	6	6
Carbon-14	6	8

同位素	质子数	中子数
碳-12	6	6
碳-14	6	8

Isotopes of the same element have identical chemical properties because chemical behaviour depends on the number of electrons. However, their physical properties such as density and melting point may differ.

同种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。然而，它们的物理性质如密度和熔点可能会有所不同。

4. Electron Configuration | 电子排布

Electrons occupy specific energy levels, often called shells. Electrons fill the lowest available energy level first. The first shell holds a maximum of 2 electrons, the second shell holds up to 8, and the third shell also holds up to 8 for the first 18 elements.

电子占据特定的能级，通常称为电子壳层。电子最先填充能量最低的壳层。第一层最多容纳 2 个电子，第二层最多容纳 8 个电子，对于前 18 种元素，第三层也最多容纳 8 个电子。

For example, the electron configuration of oxygen (atomic number 8) is 2,6:

例如，氧（原子序数 8）的电子排布为 2,6：

Electron configuration of O = 2, 6

氧的电子排布 = 2, 6

Group number (for main groups) equals the number of electrons in the outermost shell. Period number equals the number of occupied shells.

（对于主族而言）族序数等于最外层电子数。周期数等于已占据的电子壳层数。

5. Ions and Ionic Bonds | 离子与离子键

Atoms can lose or gain electrons to achieve a full outer shell, forming charged particles called ions. Metals typically lose electrons to form positive ions (cations), while non-metals gain electrons to form negative ions (anions).

原子可以通过失去或获得电子来获得满外层电子结构，从而形成带电粒子，即离子。金属通常失去电子形成正离子（阳离子），而非金属获得电子形成负离子（阴离子）。

Na → Na⁺ + e⁻

Cl + e⁻ → Cl⁻

Ionic bonding is the strong electrostatic attraction between oppositely charged ions. This occurs between a metal and a non-metal. For example, sodium chloride is formed when sodium transfers one electron to chlorine.

离子键是带相反电荷的离子之间强烈的静电吸引作用。它通常发生在金属与非金属之间。例如，氯化钠形成时，钠将一个电子转移给氯。

6. Covalent Bonds | 共价键

A covalent bond is formed when two non-metal atoms share a pair of electrons. This shared pair of electrons gives each atom a stable electron arrangement.

共价键是两个非金属原子共享一对电子时形成的化学键。共享的电子对使每个原子都达到稳定的电子构型。

Examples include hydrogen (H₂), water (H₂O), and methane (CH₄).

例如氢气（H₂）、水（H₂O）和甲烷（CH₄）。

H· + ·H → H:H

In a simple molecular substance, the covalent bonds within the molecule are strong, but intermolecular forces are weak, leading to low melting and boiling points.

在简单的分子物质中，分子内部的共价键很强，但分子间作用力较弱，因此熔点和沸点较低。

7. Metallic Bonding | 金属键

Metallic bonding occurs in metals, where positive metal ions are surrounded by a “sea” of delocalised electrons. These free electrons come from the outer shells of metal atoms.

金属键存在于金属中，正金属离子被“离域电子海”包围。这些自由电子来自金属原子的最外层。

The electrostatic attraction between the positively charged ions and the negatively charged delocalised electrons holds the structure together.

带正电荷的离子与带负电荷的离域电子之间的静电引力把金属结构结合在一起。

This model explains many properties of metals, including electrical conductivity, thermal conductivity, malleability, and ductility.

这一模型可以解释金属的许多性质，包括导电性、导热性、可延展性和可锻性。

8. Relative Atomic Mass | 相对原子质量

The relative atomic mass (Aᵣ) of an element is the weighted mean mass of its isotopes compared with one-twelfth the mass of a carbon-12 atom.

相对原子质量（Aᵣ）是指元素的同位素相对于碳-12 原子质量的十二分之一的加权平均质量。

Aᵣ = (mass of isotope₁ × abundance₁ + mass of isotope₂ × abundance₂) / 100

Aᵣ =（同位素₁的质量 × 丰度₁ + 同位素₂的质量 × 丰度₂）÷ 100

For example, chlorine has two isotopes: chlorine-35 (75%) and chlorine-37 (25%).

例如，氯有两种同位素：氯-35（占 75%）和氯-37（占 25%）。

Aᵣ = (35 × 75 + 37 × 25) / 100 = (2625 + 925) / 100 = 35.5

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

This is why the relative atomic mass of chlorine is shown as 35.5 on the periodic table.

这就是为什么氯的相对原子质量在元素周期表中显示为 35.5。

9. Periodic Table Trends | 元素周期表趋势

The periodic table arranges elements in order of increasing atomic number. Elements are placed in periods (rows) and groups (columns) based on their electron configuration.

元素周期表按原子序数递增的顺序排列元素。元素根据其电子排布被安排在周期（横行）和族（纵列）中。

Across a period, the number of protons increases, causing a stronger attraction between the nucleus and the outer electrons. This results in a decrease in atomic radius and an increase in ionisation energy.

同一周期从左到右，质子数增加，导致原子核对外层电子的引力增强。因此原子半径减小，电离能增大。

Down a group, each element has an additional electron shell, so the atomic radius increases. The outer electrons are further from the nucleus and are shielded by inner electrons, making them easier to remove.

同一族从上到下，每个元素增加一个电子壳层，因此原子半径增大。外层电子离核更远，受到内层电子的屏蔽，因此更容易失去电子。

For example, group 1 elements (alkali metals) are highly reactive and become more reactive as you go down the group because the outer electron is more easily lost.

例如，第 1 族元素（碱金属）非常活泼，且从上到下反应性增强，因为最外层电子更容易失去。

10. Calculating Protons, Neutrons, and Electrons | 计算质子、中子和电子

For a neutral atom:

对于电中性原子：

Number of protons = atomic number
Number of electrons = atomic number
Number of neutrons = mass number – atomic number

质子数 = 原子序数
电子数 = 原子序数
中子数 = 质量数 – 原子序数

For an ion, the number of electrons changes. A positive ion (cation) has fewer electrons than protons. A negative ion (anion) has more electrons than protons.

对于离子，电子数会发生变化。正离子（阳离子）的电子数少于质子数。负离子（阴离子）的电子数多于质子数。

Example: Calculate the number of subatomic particles in an aluminium ion, Al³⁺, with a mass number of 27.

例：计算质量数为 27 的铝离子 Al³⁺ 中的亚原子粒子数。

Protons = 13, Neutrons = 27 – 13 = 14, Electrons = 13 – 3 = 10

质子 = 13，中子 = 27 – 13 = 14，电子 = 13 – 3 = 10

Remember that the number of protons identifies the element, and the arrangement of electrons controls its chemical reactivity.

请记住，质子数决定了元素种类，而电子排布决定了其化学活泼性。

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Atomic Structure | 原子结构