📚 Year 8 Edexcel Chemistry Quick Reference Handbook: Formulas and Theorems | 八年级爱德思化学：公式定理速查手册
This handbook provides a concise summary of essential formulas, laws, and key concepts for Year 8 Edexcel Chemistry. It covers atomic theory, chemical equations, reaction types, and the reactivity of acids that you will encounter throughout the course. Use this quick reference to reinforce your understanding and prepare for assessments.
本手册为八年级爱德思化学的重要公式、定律和核心概念提供简明总结。内容涵盖原子理论、化学方程式、反应类型以及酸的化学性质，帮助你巩固知识、备考评估。
1. Atomic Structure | 原子结构
All matter is made of atoms, which consist of a central nucleus surrounded by electrons. The nucleus contains protons and neutrons.
所有物质由原子构成，原子由中心的原子核和绕核运动的电子组成。原子核包含质子和中子。
Protons have a relative mass of 1 and a charge of +1. Neutrons have a mass of 1 and no charge. Electrons have a negligible mass (about 1/1836 of a proton) and a charge of −1.
质子的相对质量为1，带一个单位正电荷。中子的相对质量为1，不带电。电子的质量可忽略（约为质子质量的1/1836），带一个单位负电荷。
Atoms are electrically neutral because the number of protons equals the number of electrons.
原子是电中性的，因为质子数与电子数相等。
The atomic number (Z) is the number of protons in an atom, which determines the element. The mass number (A) is the total number of protons and neutrons.
原子序数（Z）是原子中的质子数，决定了元素种类。质量数（A）等于质子数加中子数。
Electrons are arranged in shells (energy levels) around the nucleus. The first shell holds up to 2 electrons, the second up to 8, and for the first 20 elements the third shell also holds up to 8 electrons.
电子在原子核外的电子层上排布。第一层最多容纳2个电子，第二层最多8个，前20号元素的第三层最多容纳8个电子。
2. Elements, Compounds and Mixtures | 元素、化合物与混合物
An element is a pure substance made of only one type of atom. Examples include oxygen (O₂), iron (Fe) and gold (Au).
元素是由同一种原子组成的纯净物。例如氧气（O₂）、铁（Fe）和金（Au）。
A compound is a substance formed when two or more different elements are chemically bonded together. Compounds have a fixed composition and can be represented by a chemical formula, e.g. H₂O, CO₂.
化合物是由两种或以上不同元素通过化学键结合而成的物质。化合物有固定的组成，可用化学式表示，如H₂O、CO₂。
A mixture consists of two or more substances (elements or compounds) that are not chemically combined. Mixtures can be separated by physical methods such as filtration, distillation or chromatography.
混合物由两种或以上物质（元素或化合物）混合而成，它们之间
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