📚 Year 9 CIE Chemistry Formula & Theorem Quick-Reference Handbook | 九年级CIE化学：公式定理速查手册
Welcome to your Year 9 CIE Chemistry Quick-Reference Handbook. This guide compiles the essential formulas, theorems, and principles you need to master for your chemistry studies. Use it to revise atomic structure, chemical calculations, key laws, and reactivity concepts.
欢迎使用九年级CIE化学速查手册。本手册汇编了化学学习中必须掌握的核心公式、定理与原理，涵盖原子结构、化学计算、重要定律及反应活性概念，方便复习巩固。
1. Atomic Structure and Isotopes | 原子结构与同位素
Atomic number (Z) = number of protons in the nucleus.
原子序数（Z）= 原子核内的质子数。
In a neutral atom, the number of electrons equals the atomic number Z.
在电中性原子中，电子数等于原子序数Z。
Mass number (A) = total number of protons + neutrons.
质量数（A）= 质子数与中子数之和。
Number of neutrons = A – Z.
中子数 = A – Z。
Isotopes are atoms of the same element with the same Z but different A due to variable neutron numbers.
同位素是具有相同原子序数Z但因子数不同而质量数A不同的同种元素的原子。
Electron shells: first holds up to 2 e⁻, second up to 8 e⁻, third up to 8 e⁻ (valid for elements 1-20).
电子层排布：第一层最多容纳2个电子，第二层最多8个，第三层最多8个（适用于1-20号元素）。
Valence electrons = electrons in the outermost shell; they determine an element's chemical properties.
价电子 = 最外层电子；它们决定元素的化学性质。
2. Ionic Charges and Chemical Formulae | 离子电荷与化学式
To write a correct formula, learn the charges of common ions. The overall charge of a compound must be zero.
要书写正确的化学式，需熟记常见离子的电荷。化合物总电荷必须为零。
| Cation / 阳离子 | Symbol | Anion / 阴离子 | Symbol |
|---|---|---|---|
| Sodium / 钠 | Na⁺ | Chloride / 氯离子 | Cl⁻ |
| Potassium / 钾 | K⁺ | Bromide / 溴离子 | Br⁻ |
| Magnesium / 镁 | Mg²⁺ | Iodide / 碘离子 | I⁻ |
| Calcium / 钙 | Ca²⁺ | Oxide / 氧离子 | O²⁻ |
| Aluminium / 铝 | Al³⁺ | Sulfide / 硫离子 | S²⁻ |
| Ammonium / 铵根 | NH₄⁺ | Nitrate / 硝酸根 | NO₃⁻ |
| Hydrogen / 氢 | H⁺ | Sulfate / 硫酸根 | SO₄²⁻ |
| Copper(II) / 铜(II) | Cu²⁺ | Carbonate / 碳酸根 | CO₃²⁻ |
| Iron(II) / 铁(II) | Fe²⁺ | Hydroxide / 氢氧根 | OH⁻ |
Use the crossing-over method: the magnitude of the charge on one ion becomes the subscript of the other ion. Reduce to the simplest ratio.
使用交叉法：一个离子的电荷绝对值成为另一个离子的下标。化简至最简整数比。
Example: Al³⁺ and O²⁻ → Al₂O₃.
例如：Al³⁺ 与 O²⁻ → Al₂O₃。
3. Relative Atomic and Molecular Masses | 相对原子质量与相对分子质量
Relative atomic mass (Ar) is the average mass of an atom of an element compared to 1/12 of the mass of a carbon‑12 atom.
相对原子质量（Ar）是某元素一个原子的平均质量相对于一个碳‑12原子质量的1/12的比值。
Ar has no unit. It is found on the periodic table.
Ar 没有单位，可在元素周期表中找到。
Relative molecular mass (Mr) = sum of the Ar values of all atoms in the chemical formula.
相对分子质量（Mr）= 化学式中所有原子的相对原子质量之和。
Example: Mr(H₂O) = 2×1 + 16 = 18.
例如：Mr(H₂O) = 2×1 + 16 = 18。
For ionic compounds, we use relative formula mass (same calculation as Mr).
对于离子化合物，我们使用相对式量（计算方式与Mr相同）。
4. Balancing Chemical Equations | 配平化学方程式
Atoms cannot be created or destroyed, so the number of each type of atom must be the same on both sides of the equation.
原子不可创造或毁灭，因此方程式两边每种原子的数目必须相等。
Only change the coefficients (large numbers in front), never alter the subscripts in the chemical formulae.
只可改动化学式前的系数（大数字），绝不可改动化学式中的下标。
Example: H₂ + O₂ → H₂O should be balanced as 2H₂ + O₂ → 2H₂O.
例如：H₂ + O₂ → H₂O 应配平为 2H₂ + O₂ → 2H₂O。
Check each element systematically; leave hydrogen and oxygen for last if possible.
系统检查每种元素；尽可能最后配平氢和氧。
5. The Law of Conservation of Mass | 质量守恒定律
In a chemical reaction, the total mass of reactants equals the total mass of products.
在化学反应中，反应物的总质量等于生成物的总质量。
This law holds because atoms are simply rearranged, not gained or lost.
该定律成立是因为原子仅仅重新排列，不会增加或消失。
If a reaction seems to lose mass, it is often because a gas has escaped into the surroundings.
如果反应似乎质量减少，通常是因为有气体逸散到环境中。
In a closed system, the mass stays constant before and after the reaction.
在封闭系统中，反应前后的质量保持不变。
6. The Mole Concept and Basic Calculations | 摩尔概念与基础计算
One mole is the amount of substance that contains 6.02 × 10²³ particles (Avogadro's constant).
1摩尔是含有6.02 × 10²³个微粒（阿伏伽德罗常数）的物质的量。
n = m / M
n = m / M （物质的量 = 质量 / 摩尔质量）
Where M = molar mass (g/mol), numerically equal to Mr or Ar.
其中 M = 摩尔质量（g/mol），数值上等于Mr或Ar。
At room temperature and pressure (RTP), 1 mole of any gas occupies 24 dm³.
在常温常压下，1摩尔任何气体的体积为24 dm³。
V(gas) = n × 24 dm³
V(气体) = n × 24 dm³
Concentration (mol/dm³): c = n / V, where V is volume of solution in dm³.
浓度（mol/dm³）：c = n / V，其中V为溶液体积，单位dm³。
These relationships allow you to convert between mass, moles, volume of gas, and concentration.
这些关系式可实现质量、物质的量、气体体积和浓度之间的换算。
7. Reactivity Series and Displacement Reactions | 金属活动性顺序与置换反应
The reactivity series ranks metals by their tendency to lose electrons and form positive ions.
金属活动性顺序根据金属失去电子形成阳离子的倾向大小排列。
Series (highest to lowest): K, Na, Ca, Mg, Al, Zn, Fe, Sn, Pb, (H), Cu, Ag, Au.
顺序（由高到低）：钾、钠、钙、镁、铝、锌、铁、锡、铅、（氢）、铜、银、金。
A more reactive metal displaces a less reactive metal from its compound in aqueous solution or molten form.
较活泼的金属能从水溶液或熔融状态中置换出较不活泼的金属。
Example: Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s). Zinc is more reactive than copper.
例如：Zn(s) + CuSO₄(aq) → ZnSO₄(aq) + Cu(s)，锌比铜更活泼。
Hydrogen is included in the series; metals above hydrogen can displace it from acids.
氢包含在顺序中；位于氢之前的金属可以从酸中置换出氢气。
8. Acids, Bases and the pH Scale | 酸、碱与pH值
An acid is a proton (H⁺) donor. A base is a proton acceptor. Alkalis are soluble bases that release OH⁻ ions in water.
酸是质子（H⁺）供体。碱是质子受体。可溶性碱在水中释放OH⁻离子，称为alkali。
The pH scale runs from 0 to 14: pH < 7 acidic
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