📚 Year 8 OCR Chemistry: Quick Reference Handbook of Formulas and Theorems | Year 8 OCR 化学：公式定理速查手册
Chemistry is the science that explains what everything around us is made of and how substances change. For Year 8 students following the OCR curriculum, having a clear set of core formulas, laws and models is the key to mastering topics from atoms and elements to reactions and equations. This handbook brings together the essential chemical rules, notation and principles you need to solve problems and describe the world at the particle level.
化学是解释我们周围一切由什么构成以及物质如何变化的科学。对于学习 OCR 课程的 Year 8 学生来说，掌握一套清晰的核心公式、定律和模型，是精通原子、元素、反应和方程式等主题的关键。这本手册汇集了你解决问题和在粒子层面描述世界所需的基本化学规则、符号和原理。
1. Atoms, Elements and Compounds | 原子、元素与化合物
All matter is made of atoms. An element is a substance composed of only one type of atom, such as oxygen (O) or iron (Fe). When two or more different elements chemically bond together in a fixed ratio, they form a compound, like water (H₂O) or carbon dioxide (CO₂). Mixtures contain different substances that are not chemically combined and can be separated by physical methods.
所有物质都由原子组成。元素是仅由一种原子构成的物质，如氧（O）或铁（Fe）。当两种或多种不同元素以固定比例通过化学键结合时，就形成化合物，如水（H₂O）或二氧化碳（CO₂）。混合物含有未通过化学键结合的不同物质，可以通过物理方法分离。
2. Atomic Structure and Subatomic Particles | 原子结构与亚原子粒子
An atom consists of a central nucleus containing protons (positive charge) and neutrons (neutral), surrounded by electrons (negative charge) arranged in shells. The atomic number (Z) equals the number of protons, which defines the element. The mass number (A) is the total number of protons plus neutrons.
原子由一个包含质子（带正电）和中子（不带电）的中央原子核以及按电子层排列的电子（带负电）组成。原子序数（Z）等于质子数，它决定了元素的种类。质量数（A）是质子数与中子数的总和。
The first electron shell can hold up to 2 electrons, the second up to 8, and the third up to 8 for the first 20 elements. Electronic configuration is written as, for example, 2,8,1 for sodium (Na). Electrons in the outermost shell are called valence electrons and determine chemical properties.
第一电子层最多容纳 2 个电子，第二层最多 8 个，前 20 号元素的第三层最多 8 个。电子排布写作如钠（Na）的 2,8,1。最外层的电子称为价电子，决定化学性质。
3. The Periodic Table and Group Properties | 元素周期表与族性质
The periodic table arranges elements in order of increasing atomic number. Horizontal rows are called periods; vertical columns are groups. Elements in the same group have the same number of valence electrons, giving them similar chemical behaviour.
元素周期表按原子序数递增排列元素。横行称为周期，纵列称为族。同一族元素具有相同的价电子数，因此化学性质相似。
Key groups for Year 8 include Group 1 (alkali metals, very reactive, 1 valence electron), Group 7 (halogens, reactive non-metals, 7 valence electrons) and Group 0/8 (noble gases, unreactive, full outer shell). The reactivity of Group 1 metals increases down the group, while reactivity of Group 7 decreases down the group.
Year 8 需重点掌握的族包括：第 1 族（碱金属，非常活泼，有 1 个价电子）、第 7 族（卤素，活泼非金属，7 个价电子）和第 0/8 族（稀有气体，不活泼，最外层全满）。第 1 族金属的活泼性沿族向下增强，而第 7 族的活泼性则向下减弱。
4. Chemical Formulae and Naming Compounds | 化学式与化合物命名
A chemical formula uses element symbols and subscript numbers to show the types and ratios of atoms in a compound. The formula of an ionic compound is determined by balancing the charges of the positive cation and negative anion. For example, sodium chloride is NaCl because Na⁺ and Cl⁻ combine in a 1:1 ratio.
化学式用元素符号和下标数字表示化合物中原子的种类和个数比例。离子化合物的化学式通过平衡阳离子和阴离子的电荷来确定。例如，氯化钠是 NaCl，因为 Na⁺ 与 Cl⁻ 以 1:1 比例结合。
When naming simple binary compounds, the metal goes first, followed by the non-metal with an ‘-ide’ ending: magnesium + oxygen → magnesium oxide (MgO). For compounds containing polyatomic ions, learn common ions such as sulfate SO₄²⁻, nitrate NO₃⁻, carbonate CO₃²⁻ and hydroxide OH⁻. Brackets are used when more than one polyatomic ion is needed, e.g. Ca(OH)₂.
给简单二元化合物命名时，金属在前，非金属在后，并以“-ide”结尾：镁 + 氧 → 氧化镁（MgO）。含有原子团的化合物需熟记常见离子，如硫酸根 SO₄²⁻、硝酸根 NO₃⁻、碳酸根 CO₃²⁻ 和氢氧根 OH⁻。需要多个原子团时使用括号，例如 Ca(OH)₂。
5. Writing and Balancing Chemical Equations | 化学方程式的书写与配平
A word equation describes a reaction using the names of reactants and products. A symbol equation replaces names with chemical formulae and must be balanced to obey the law of conservation of mass. Balancing means ensuring the same number of each type of atom appears on both sides of the arrow.
文字方程式用反应物和生成物的名称描述反应。符号方程式用化学式代替名称，且必须配平以遵守质量守恒定律。配平意味着确保箭头两边每种原子的个数相等。
State symbols are added in brackets: (s) for solid, (l) for liquid, (g) for gas, and (aq) for aqueous (dissolved in water). For example, the balanced equation for the reaction of hydrogen with oxygen is: 2H₂(g) + O₂(g) → 2H₂O(l). Always adjust only the large coefficients in front of formulae, never alter the subscripts inside a formula.
状态符号加在括号中：(s) 表示固体，(l) 表示液体，(g) 表示气体，(aq) 表示水溶液。例如，氢气与氧气反应的配平方程式为：2H₂(g) + O₂(g) → 2H₂O(l)。始终只调整化学式前面的大系数，绝不能改动化学式内部的下标。
6. Law of Conservation of Mass | 质量守恒定律
The total mass of reactants equals the total mass of products in a chemical reaction. No atoms are created or destroyed; they are only rearranged. This principle underpins all balanced equations and helps explain why the mass seems to change in open systems when a gas escapes or enters.
化学反应中，反应物的总质量等于生成物的总质量。原子没有被创造或消灭，只是重新组合。这一原理是所有配平方程式的基础，并解释了在敞开体系中，当气体逸出或进入时，为何质量似乎发生变化。
In a closed system, mass stays constant throughout. For example, when a metal reacts with oxygen from the air, the product appears heavier because oxygen atoms have been added. Conversely, heating a carbonate in an open container leads to a mass loss as carbon dioxide gas escapes.
在密闭体系中，质量始终保持不变。例如，金属与空气中的氧气反应，产物看起来更重，因为加入了氧原子。反之，在开放容器中加热碳酸盐，由于二氧化碳气体逸出，质量会减少。
7. Types of Chemical Reactions | 化学反应类型
Recognising reaction patterns helps predict products. The main types for Year 8 include: combination (synthesis), where two or more substances form one product; decomposition, where one compound breaks into simpler substances; combustion, the rapid reaction of a substance with oxygen releasing heat and light; and displacement, where a more reactive element pushes out a less reactive one from its compound.
认识反应类型有助于预测产物。Year 8 需要掌握的主要类型包括：化合反应（合成），两种或多种物质生成一种产物；分解反应，一种化合物分解为更简单的物质；燃烧，物质与氧气快速反应并释放热和光；以及置换反应，较活泼的元素将较不活泼的元素从其化合物中置换出来。
A neutralisation reaction between an acid and a base produces a salt and water. Thermal decomposition is a type of decomposition driven by heat, such as copper carbonate → copper oxide + carbon dioxide. Always link the reaction type to the rearrangement of atoms.
酸与碱之间的中和反应生成盐和水。热分解是受热驱动的分解反应，例如碳酸铜 → 氧化铜 + 二氧化碳。始终将反应类型与原子的重新组合联系起来。
8. Acids, Bases and the pH Scale | 酸、碱与 pH 标度
Acids are substances that release hydrogen ions (H⁺) in water; they have a sour taste, turn blue litmus red and have a pH less than 7. Common laboratory acids include hydrochloric acid (HCl), sulfuric acid (H₂SO₄) and nitric acid (HNO₃). Bases neutralise acids; alkalis are soluble bases that release hydroxide ions (OH⁻) in water, feel soapy and turn red litmus blue, with a pH greater than 7.
酸是在水中释放氢离子（H⁺）的物质；它们有酸味，使蓝色石蕊试纸变红，pH 小于 7。实验室常见酸包括盐酸（HCl）、硫酸（H₂SO₄）和硝酸（HNO₃）。碱能中和酸；可溶的碱称为碱，在水中释放氢氧根离子（OH⁻），手感滑腻，使红色石蕊试纸变蓝，pH 大于 7。
The pH scale runs from 0 (very acidic) to 14 (very alkaline), with 7 being neutral. Universal indicator and pH probes give precise pH values. Concentrated acids and alkalis are corrosive and must be handled safely.
pH 标度范围为 0（强酸）到 14（强碱），7 为中性。通用指示剂和 pH 计能给出精确的 pH 值。浓酸和浓碱具有腐蚀性，必须安全操作。
9. Neutralisation and Making Salts | 中和反应与盐的制备
Neutralisation is a reaction between an acid and a base (or alkali) that produces a salt and water. The general equation is: acid + base → salt + water. For example, hydrochloric acid + sodium hydroxide → sodium chloride + water: HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l).
中和是酸与碱（或碱）反应生成盐和水的过程。通用方程式为：酸 + 碱 → 盐 + 水。例如，盐酸 + 氢氧化钠 → 氯化钠 + 水：HCl(aq) + NaOH(aq) → NaCl(aq) + H₂O(l)。
Salts are named after the acid and the metal in the base: hydrochloric acid produces chlorides, sulfuric acid produces sulfates, nitric acid produces nitrates. To produce a pure, dry salt, you can use filtration and evaporation or crystallisation, depending on the solubility of the salt.
盐的命名依据所用酸和碱中的金属：盐酸生成氯化物，硫酸生成硫酸盐，硝酸生成硝酸盐。要制备纯净干燥的盐，可根据盐的溶解度采用过滤和蒸发或结晶的方法。
10. Reactivity Series of Metals | 金属活动性顺序
The reactivity series ranks metals by how readily they react. A more reactive metal can displace a less reactive metal from its compound. The order, starting with the most reactive: potassium (K), sodium (Na), calcium (Ca), magnesium (Mg), aluminium (Al), zinc (Zn), iron (Fe), lead (Pb), (hydrogen, H, for comparison), copper (Cu), silver (Ag), gold (Au).
金属活动性顺序根据金属反应的难易程度排序。较活泼的金属能将较不活泼的金属从其化合物中置换出来。顺序从最活泼开始：钾（K）、钠（Na）、钙（Ca）、镁（Mg）、铝（Al）、锌（Zn）、铁（Fe）、铅（Pb）、（氢，H，用于比较）、铜（Cu）、银（Ag）、金（Au）。
Metals above hydrogen in the series react with dilute acids to produce hydrogen gas and a salt. The test for hydrogen is a ‘squeaky pop’ with a lit splint. Only metals below hydrogen, like copper, do not react with dilute acids.
活动性顺序中排在氢之前的金属能与稀酸反应生成氢气和盐。检验氢气的方法是用点燃的木条靠近，会发出“噗”的爆鸣声。只有排在氢之后的金属，如铜，才不与稀酸反应。
11. Calculations Using Chemical Equations | 利用化学方程式的计算
Using balanced equations and relative atomic masses (Aᵣ), you can calculate the masses of reactants and products. Relative atomic mass is the average mass of an atom of an element compared to 1/12 of the mass of a carbon-12 atom. The relative formula mass (Mᵣ) of a compound is the sum of the Aᵣ of all atoms in its formula.
利用配平的方程式和相对原子质量（Aᵣ），可以计算反应物和生成物的质量。相对原子质量是一个元素原子的平均质量与碳-12 原子质量的 1/12 相比得到的值。化合物的相对式量（Mᵣ）是其化学式中所有原子 Aᵣ 的总和。
Example: to find the mass of magnesium oxide produced when 24g of magnesium burns completely in oxygen (2Mg + O₂ → 2MgO), first find Mᵣ: MgO = 24 + 16 = 40. From the equation, 2 moles of Mg (2×24=48g) produce 2 moles of MgO (2×40=80g). So 24g of Mg produces (24/48)×80 = 40g of MgO.
示例：计算 24g 镁在氧气中完全燃烧生成氧化镁的质量（2Mg + O₂ → 2MgO）。首先计算 Mᵣ：MgO = 24 + 16 = 40。由方程式可知，2 mol Mg（2×24=48g）生成 2 mol MgO（2×40=80g）。因此 24g Mg 生成 (24/48)×80 = 40g MgO。
These simple proportion calculations do not require the mole concept; they rely on the fixed mass ratios in balanced equations, which directly follow from conservation of mass.
这些简单的比例计算不需要引入摩尔概念，它们依据的是配平方程式中固定的质量比，这正是质量守恒定律的直接体现。
12. Key Theorems and Models | 重要定理与模型
Dalton’s atomic theory: all matter is made of tiny indivisible particles called atoms; atoms of the same element are identical; atoms combine in simple whole-number ratios to form compounds. Although we now know atoms can be split, this model explains the law of conservation of mass and the law of constant composition (a given compound always contains the same elements in the same proportion by mass).
道尔顿原子理论：所有物质都由称为原子的、不可分割的微粒组成；同种元素的原子完全相同；原子以简单的整数比结合形成化合物。尽管我们现在知道原子可以再分，但这一模型解释了质量守恒定律和定组成定律（某种化合物总是含有相同质量比例的相同元素）。
The kinetic particle model states that all particles are in constant motion; the energy of motion increases with temperature. This model explains changes of state, diffusion and gas pressure. In a solid, particles vibrate in fixed positions; in a liquid, they move past each other; in a gas, they move rapidly and randomly.
运动粒子模型指出，所有粒子都在不停地运动；运动能量随温度升高而增加。该模型解释了状态变化、扩散和气体压强。固态时，粒子在固定位置上振动；液态时，粒子相互滑动；气态时，粒子快速无规则运动。
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