📚 Year 7 SQA Chemistry: Quick Reference Handbook of Formulas and Theorems | SQA Year 7 化学：公式定理速查手册
This quick reference guide covers essential formulas, rules, and theorems in the Year 7 SQA Chemistry curriculum. Designed for revision and daily study, it brings together atomic structure, chemical formula writing, balancing equations, and key calculation methods. Keep this handbook handy to strengthen your understanding and solve problems with confidence.
这本速查手册涵盖 SQA Year 7 化学课程中的核心公式、规则与定理。它汇总了原子结构、化学式书写、方程式配平和关键计算方法，适合复习与日常学习。常备此手册，有助于加深理解并自信地解题。
1. Atomic Structure and Particle Calculation | 原子结构与粒子计算
Every atom has a small, dense nucleus containing protons and neutrons, surrounded by electrons arranged in shells. The atomic number (Z) is the number of protons, which uniquely identifies the element.
每个原子都有一个由质子和中子组成的致密小核，核外有电子分层排布。原子序数(Z)等于质子数，它决定了元素的种类。
The mass number (A) is the total number of protons and neutrons in the nucleus. To find the number of neutrons, simply use the formula:
质量数(A)是原子核内质子数与中子数之和。计算中子数时，只需使用下面的公式：
number of neutrons = A – Z
so it contains 11 protons and 11 electrons. If an atom loses or gains electrons, it becomes an ion, and the electron number changes accordingly.
在中性原子中，电子数等于质子数(Z)。例如，钠原子的 Z = 11，因此它有 11 个质子和 11 个电子。如果原子得到或失去电子，就会变成离子，此时电子数随之改变。
The elemental symbol often appears with A and Z: AZX. For 2311Na, the atom has 11 protons, (23 – 11) = 12 neutrons, and 11 electrons.
元素符号常与 A 和 Z 一同给出：AZX。例如 2311Na，该原子有 11 个质子，(23 – 11) = 12 个中子，以及 11 个电子。
2. Writing Chemical Formulae – Valency Rules | 化学式书写 – 化合价规则
The chemical formula of an ionic compound is built by balancing the charges of positive and negative ions. The valency (combining power) of an ion tells you how many charges it carries.
离子化合物的化学式是通过平衡正负离子的电荷来书写的。离子的化合价（结合能力）表示它带多少个电荷。
To write the formula, use the 'cross-over' method: put the magnitude of the charge of one ion as the subscript of the other, and then simplify to the smallest whole-number ratio if necessary.
书写化学式时使用“十字交叉法”：将一个离子电荷的绝对值作为另一个离子的下标，如有公因数再化简为最小整数比。
pposite, subscript 1 is not written). For aluminium ion Al³⁺ and oxide ion O²⁻, cross the numbers: Al2O3.
例如：钠离子 Na⁺ 与氯离子 Cl⁻ → NaCl（电荷等量相反，下标 1 省略）。对于铝离子 Al³⁺ 与氧离子 O²⁻，交叉数字得到：Al2O3。
ds to appear more than once, enclose it in brackets: calcium nitrate Ca²⁺ and NO₃⁻ → Ca(NO3)2.
如果多原子离子需出现多次，要用括号括起来：钙离子 Ca²⁺ 与硝酸根 NO₃⁻ → Ca(NO3)2。
3. Common Polyatomic Ions | 常见多原子离子
Knowing these ions by heart helps you write formulae and equations quickly.
熟记以下离子有助于快速书写化学式和方程式。
| Name / 名称 | Formula | Charge |
|---|---|---|
| Hydroxide / 氢氧根 | OH⁻ | 1⁻ |
| Nitrate / 硝酸根 | NO₃⁻ | 1⁻ |
| Carbonate / 碳酸根 | CO₃²⁻ | 2⁻ |
| Sulfate / 硫酸根 | SO₄²⁻ | 2⁻ |
| Ammonium / 铵根 | NH₄⁺ | 1⁺ |
Always apply brackets when more than one polyatomic ion is used, e.g. ammonium sulfate: (NH4)2SO4.
当需要多个多原子离子时，务必使用括号，例如硫酸铵：(NH4)2SO4。
4. Balancing Chemical Equations | 化学方程式的配平
A balanced chemical equation shows the same number of each type of atom on both sides, reflecting the Law of Conservation of Mass. Never change chemical formulae to balance; only add coefficients in front.
配平的化学方程式两边同种原子的数目相等，体现了质量守恒定律。配平时绝不可改动化学式本身，只能在前面添加系数。
Use the following steps: first balance metals, then non-metals (except oxygen and hydrogen), then balance hydrogen and finally oxygen. Check that all coefficients are in the simplest whole-number ratio.
按以下步骤进行：先配平金属原子，再配平非金属（氧和氢除外），然后配平氢，最后配平氧。检查所有系数是否已化为最小整数比。
Example: H2 + O2 → H2O. Start with H: 2 on each side, but oxygen: 2 on left, 1 on right. Put 2 before H2O to get O2 → 2H2O (now H: 4 on right). Adjust H2 on left to 2: 2H2 + O2 → 2H2O.
示例：H2 + O2 → H2O。先看 H：左右各 2 个，但氧原子左边 2 个，右边 1 个。在 H2O 前加系数 2 得 O2 → 2H2O（此时右边 H 变成 4）。再将左边 H2 配系数 2：2H2 + O2 → 2H2O。
5. Law of Conservation of Mass | 质量守恒定律
In a chemical reaction, atoms are neither created nor destroyed. The total mass of reactants always equals the total mass of products.
化学反应中，原子既不会凭空产生也不会消失。反应物的总质量始终等于生成物的总质量。
This principle is why we must balance equations. If 4 g of hydrogen react completely with 32 g of oxygen, exactly 36 g of water is formed. Any apparent mass change in an open container is usually due to gas entering or leaving.
正是这一原理要求我们必须配平方程式。若 4 克氢气与 32 克氧气恰好完全反应，则必定生成 36 克水。在开放容器中若质量有表观变化，往往是气体进入或逸散所致。
6. Relative Atomic Mass (Ar) and Relative Formula Mass (Mr) | 相对原子质量与相对式量
The relative atomic mass (Ar) is the average mass of an atom compared to 1/12 of the mass of a carbon‑12 atom. It has no units. You find Ar values on the Periodic Table.
相对原子质量(Ar)是原子的平均质量与碳‑12 原子质量的 1/12 相比的比值，没有单位。Ar 数值可从元素周期表上获得。
The relative formula mass (Mr) is the sum of all the Ar in a chemical formula. For covalent molecules you may call it relative molecular mass.
相对式量(Mr)是化学式中所有原子的 Ar 之和。对共价分子也可称为相对分子质量。
Mr = ∑ (number of atoms × Ar)
Example: H2O (Ar: H = 1, O = 16) → Mr = (2 × 1) + (1 × 16) = 18. CO2 (C = 12, O = 16) → Mr = 12 + (2 × 16) = 44.
示例：H2O（Ar值：H=1，O=16）→ Mr = (2 × 1) + (1 × 16) = 18。CO2（C=12，O=16）→ Mr = 12 + (2 × 16) = 44。
7. Percentage Composition of a Compound | 化合物中元素的百分含量
Percentage composition tells you what proportion of the total mass each element contributes.
百分含量表明各元素在总质量中所占的比例。
% mass of element = (total Ar of that element ÷ Mr of compound) × 100%
Example: In H2O, total mass of H = 2 × 1 = 2. Mr = 18. % H = (2 ÷ 18) × 100% = 11.1%. The rest is oxygen.
示例：水中，H 的总质量 = 2 × 1 = 2，Mr = 18。则 % H = (2 ÷ 18) × 100% = 11.1%。其余为氧。
8. States of Matter and Symbols | 物质状态与符号
In chemical equations, we indicate the physical state of each substance using symbols in parentheses. This is important for understanding reaction conditions.
化学方程式中，我们用括号中的符号标示各物质的物理状态，这有助于理解反应条件。
| Symbol | State / 状态 |
|---|---|
| (s) | solid / 固体 |
| (l) | liquid / 液体 |
| (g) | gas / 气体 |
| (aq) | aqueous (dissolved in water) / 水溶液 |
Example: 2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g). The symbols tell you sodium is solid, water is liquid, and hydrogen gas bubbles off.
示例：2Na(s) + 2H2O(l) → 2NaOH(aq) + H2(g)。状态符号告诉我们钠是固体、水是液体、生成的氢气以气泡逸出。
9. Reaction Types and Patterns | 反应类型与规律
Recognising patterns helps you predict products. Below are common reaction types studied in Year 7.
辨识规律有助于预测产物。以下是 Year 7 常见的反应类型。
Combination (synthesis): two or more substances join to form one product. A + B → AB. E.g. 2H2 + O2 → 2H2O.
化合反应：两种或多种物质结合生成一种产物。A + B → AB。如 2H2 + O2 → 2H2O。
Decomposition: a single compound breaks down into two or more simpler substances. AB → A + B. E.g. CaCO3 → CaO + CO2 (thermal decomposition).
分解反应：一种化合物分解成两种或多种较简单的物质。AB → A + B。如 CaCO3 → CaO + CO2（热分解）。
Displacement (metal + acid): eactive metal pushes a less reactive metal or hydrogen out of a compound. Zn + 2HCl → ZnCl2 + H2.
置换反应（金属与酸）：较活泼金属将氢或较不活泼金属从化合物中置换出来。Zn + 2HCl → ZnCl2 + H2。
Neutralisation: acid + base → salt + water. E.g. HCl + NaOH → NaCl + H2O.
中和反应：酸 + 碱
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