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

This revision guide covers the core atomic structure and periodic table content needed for Edexcel A-level combined science study: nuclear structure, electron configuration, isotope calculations, periodic trends, ionisation energy, and key group chemistry. It is designed to help you convert descriptive ideas into precise, exam-ready explanations.

本复习指南涵盖 Edexcel A-level 综合科学学习所需的原子结构与元素周期表核心内容：原子核结构、电子排布、同位素计算、周期趋势、电离能以及重要族化学。它旨在帮助你把描述性概念转化为精确、适合考试的解答。

1. The Nuclear Model of the Atom | 原子的核模型

Atoms contain three sub-atomic particles: protons and neutrons in the nucleus, and electrons arranged around the nucleus. Protons carry a positive charge, neutrons are neutral, and electrons carry a negative charge. The atom has a radius of about 10⁻¹⁰ m, while the nucleus is about 10⁻¹⁵ m, so most of the atom is empty space.

原子含有三种亚原子粒子：原子核中的质子和中子，以及围绕原子核排布的电子。质子带正电，中子不带电，电子带负电。原子的半径约为 10⁻¹⁰ m，而原子核约为 10⁻¹⁵ m，因此原子大部分是空的空间。

The strong nuclear force holds protons and neutrons together despite electrostatic repulsion between protons. The number of protons defines the element and is called the atomic number, Z. The total number of protons and neutrons is the mass number, A.

强核力将质子和中子结合在一起，克服质子之间的静电排斥。质子的数目决定了元素种类，称为原子序数 Z。质子与中子的总数为质量数 A。

proton relative mass ≈ 1, charge = +1

质子的相对质量约为 1，电荷为 +1
neutron relative mass ≈ 1, charge = 0

中子的相对质量约为 1，电荷为 0
electron relative mass ≈ 1/1836, charge = −1

电子的相对质量约为 1/1836，电荷为 −1

2. Electrons, Energy Levels and Orbitals | 电子、能级与轨道

Electrons occupy shells labelled by the principal quantum number n. Within these shells, electrons are arranged in subshells called s, p, d and f. Each orbital can hold a maximum of two electrons with opposite spin. The s subshell has one orbital, p has three, d has five, and f has seven.

电子占据由主量子数 n 标记的电子层。在这些电子层内，电子排布在称为 s、p、d、f 的亚层中。每个轨道最多容纳两个自旋相反的电子。s 亚层有 1 个轨道，p 有 3 个，d 有 5 个，f 有 7 个。

Electron configurations are built using three rules: electrons fill the lowest energy orbitals first (Aufbau principle), no two electrons in the same orbital can have the same spin (Pauli exclusion principle), and electrons occupy degenerate orbitals singly before pairing (Hund’s rule). For example, sodium has the configuration 1s²2s²2p⁶3s¹, and chlorine is 1s²2s²2p⁶3s²3p⁵.

电子排布遵循三条规则：电子优先填充能量最低的轨道（能量最低原理）、同一轨道中的两个电子自旋必须相反（泡利不相容原理）、电子在简并轨道中先单独占据再配对（洪特规则）。例如，钠的电子排布为 1s²2s²2p⁶3s¹，氯为 1s²2s²2p⁶3s²3p⁵。

Transition metals show characteristic exceptions because the 4s and 3d subshells are close in energy. Chromium is [Ar]3d⁵4s¹, and copper is [Ar]3d¹⁰4s¹, rather than the predicted 3d⁴4s² and 3d⁹4s².

过渡金属因 4s 与 3d 亚层能量接近而表现出特征性的排布例外。铬的排布为 [Ar]3d⁵4s¹，铜为 [Ar]3d¹⁰4s¹，而不是预计的 3d⁴4s² 和 3d⁹4s²。

3. Atomic Number, Mass Number and Isotopes | 原子序数、质量数与同位素

The atomic number Z is the number of protons in the nucleus. It identifies the element and determines its position in the periodic table. The mass number A is the sum of protons and neutrons. In a neutral atom, the number of electrons equals Z.

原子序数 Z 是原子核中的质子数。它决定了元素的种类及其在元素周期表中的位置。质量数 A 是质子数与中子数之和。在电中性原子中，电子数等于 Z。

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. Carbon has three naturally occurring isotopes: C-12, C-13 and C-14.

同位素是同一元素且质子数相同、但中子数不同的原子。因此它们具有相同的原子序数，但质量数不同。碳有三种天然同位素：C-12、C-13 和 C-14。

Isotopes have identical chemical properties because chemical behaviour is determined by the electron arrangement. They differ in physical properties such as mass, density and diffusion rate. This principle is important when interpreting mass spectra and tracer experiments.

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排布。它们的物理性质如质量、密度和扩散速率不同。这一原理在解释质谱和示踪实验时非常重要。

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

Relative atomic mass, Aᵣ, is the weighted average mass of an element relative to 1/12 of the mass of a carbon-12 atom. It reflects the abundance of each isotope in a natural sample.

相对原子质量 Aᵣ 是元素各同位素质量的加权平均值，相对基准为碳-12 原子质量的 1/12。它反映了天然样品中每种同位素的丰度。

The weighted average is calculated using the formula:

加权平均值由以下公式计算：

Aᵣ = Σ (isotopic mass × percentage abundance) / 100

For chlorine, 75.77% is Cl-35 and 24.23% is Cl-37. The relative atomic mass is:

以氯为例，75.77% 为 Cl-35，24.23% 为 Cl-37。其相对原子质量为：

Aᵣ(Cl) = (35 × 75.77 + 37 × 24.23) / 100 = 35.48

Mass spectrometry gives sharp peaks for each isotope. The peak height or area is proportional to abundance. In an exam, always check whether the data is given as percentages or as relative intensities.

质谱为每种同位素给出尖锐的峰。峰高或峰面积与丰度成正比。考试时务必检查数据是以百分比还是相对强度给出。

Isotope	Percentage abundance	Contribution to Aᵣ
Cl-35	75.77	26.52
Cl-37	24.23	8.97

5. The Periodic Table: Structure and Blocks | 元素周期表：结构与分区

The periodic table is arranged in order of increasing atomic number. Elements with similar outer-shell electron configurations appear in the same group, which explains similar chemical properties. Periods are horizontal rows; groups are vertical columns.

元素周期表按原子序数递增排列。外层电子排布相似的元素位于同一族，因此具有相似的化学性质。周期是水平的行，族是垂直的列。

The table is divided into s-block, p-block, d-block and f-block elements according to the subshell being filled. Group 1 and Group 2 are s-block; Groups 13 to 18 are p-block; transition elements are d-block; lanthanides and actinides are f-block.

周期表根据正在填充的亚层分为 s 区、p 区、d 区和 f 区。第 1 族和第 2 族为 s 区；第 13 至 18 族为 p 区；过渡元素为 d 区；镧系和锕系为 f 区。

The block and group of an element can be read from its outer electron configuration. For example, magnesium has configuration [Ne]3s² and is an s-block element in Group 2. Sulfur has [Ne]3s²3p⁴ and is a p-block element in Group 16.

元素的区和族可以从其外层电子排布读取。例如，镁的排布为 [Ne]3s²，是第 2 族 s 区元素。硫的排布为 [Ne]3s²3p⁴，是第 16 族 p 区元素。

6. Periodicity: Trends Across Period 3 | 周期性：第三周期的变化趋势

Across Period 3, atomic radius decreases because the nuclear charge increases while electrons are added to the same outer shell. The increased positive charge pulls the outer electrons closer without significant extra shielding from inner shells.

在第三周期从左到右，原子半径减小，因为核电荷增加而电子被添加到同一外层。增加的正电荷把外层电子拉得更近，而内层电子屏蔽没有明显增强。

Ionisation energy generally increases across the period, and electronegativity also increases. The trends are interrupted where electron pairing or a new subshell changes the energy of the electron being removed.

电离能沿周期总体上升，电负性也上升。当电子成对或进入新亚层时，被移除

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