📚 Naming Compounds: A Level Chemistry Guide | 化合物命名：A-Level 化学指南
Systematic chemical nomenclature turns potentially ambiguous formulas like FeCl₂ and FeCl₃ into precise names that reveal both composition and oxidation state. In Cambridge A Level Chemistry, you must be able to move confidently between names and formulas for ionic compounds, covalent molecules, acids, hydrated salts and simple organic species.
系统化学命名法将 FeCl₂ 与 FeCl₃ 这类可能产生歧义的化学式，转化为既能反映组成又能表明氧化态的精确名称。在剑桥 A Level 化学课程中，你需要熟练地在离子化合物、共价分子、酸、水合盐以及简单有机物的名称与化学式之间进行转换。
1. Why Systematic Naming Matters | 为什么系统命名很重要
Chemical formulas show the ratio of atoms or ions, but they do not always show the bonding type or the oxidation state of a metal. Naming rules allow chemists to communicate structure unambiguously across languages and exam papers.
化学式可以展示原子或离子的比例，但并不能总是体现成键类型或金属的氧化态。命名规则使化学工作者能够在不同语言和考试卷面中准确无误地传递结构信息。
The IUPAC system assigns one principal name to each compound, while common names such as water, ammonia and limestone are still accepted in everyday use but are not always accepted in assessments.
IUPAC 体系为每种化合物指定一个主要名称，而水、氨、石灰石等俗名在日常交流中仍然被接受，但在考试中并不总是适用。
For A Level, you need to know both the systematic name and the common names of frequently encountered laboratory substances.
在 A Level 课程中，你既需要掌握系统名称，也需要熟悉常见实验室物质的俗名。
2. Binary Ionic Compounds | 二元离子化合物
Binary ionic compounds contain a metal cation and a non-metal anion. The name places the cation first and the anion second, with the non-metal ending changed to -ide. For example, NaCl is sodium chloride, MgO is magnesium oxide, and Ca₃N₂ is calcium nitride.
二元离子化合物由一种金属阳离子和一种非金属阴离子组成。命名时阳离子在前、阴离子在后，非金属元素词尾改为 -ide。例如 NaCl 为 sodium chloride（氯化钠），MgO 为 magnesium oxide（氧化镁），Ca₃N₂ 为 calcium nitride（氮化钙）。
The formula is built by balancing total positive and negative charges. Aluminium oxide contains Al³⁺ and O²⁻, so the neutral combination is Al₂O₃.
书写化学式时需要使正负电荷总数平衡。氧化铝含有 Al³⁺ 和 O²⁻，因此电中性组合为 Al₂O₃。
Non-metal anions use predictable endings: chlorine becomes chloride, oxygen becomes oxide, nitrogen becomes nitride, sulfur becomes sulfide, and phosphorus becomes phosphide.
非金属阴离子的词尾有规律：氯变为 chloride，氧变为 oxide，氮变为 nitride，硫变为 sulfide，磷变为 phosphide。
3. Transition Metals and Oxidation States | 过渡金属与氧化态
Transition metals often form more than one stable cation, so the name must include the oxidation state as a Roman numeral in parentheses. Iron can form Fe²⁺ and Fe³⁺; FeCl₂ is iron(II) chloride and FeCl₃ is iron(III) chloride.
过渡金属通常可形成多种稳定阳离子，因此名称中必须用括号内的罗马数字标明氧化态。铁可以形成 Fe²⁺ 和 Fe³⁺；FeCl₂ 为 iron(II) chloride（氯化亚铁），FeCl₃ 为 iron(III) chloride（氯化铁）。
The Roman numeral is calculated from the known charge of the anion. In Cu₂O, the oxide ion is O²⁻, so the two copper ions must carry a total charge of +2; each copper is +1, giving copper(I) oxide.
罗马数字可根据阴离子的已知电荷计算。在 Cu₂O 中，氧离子为 O²⁻，因此两个铜离子的总电荷必须为 +2；每个铜为 +1，命名为 copper(I) oxide（氧化亚铜）。
Do not use Roman numerals for metals with fixed oxidation states, such as Group 1, Group 2, aluminium and zinc.
对于氧化态固定的金属，例如第 1 族、第 2 族、铝和锌，不要使用罗马数字。
| Formula | Name | 中文 |
|---|---|---|
| FeO | iron(II) oxide | 氧化亚铁 |
| Fe₂O₃ | iron(III) oxide | 氧化铁 |
| CuO | copper(II) oxide | 氧化铜 |
| Cu₂O | copper(I) oxide | 氧化亚铜 |
4. Polyatomic Ions | 多原子离子
Polyatomic ions are charged groups of atoms that remain intact in many reactions. Common examples include sulfate SO₄²⁻, nitrate NO₃⁻, carbonate CO₃²⁻, ammonium NH₄⁺ and hydroxide OH⁻.
多原子离子是由多个原子组成的带电基团，在许多反应中保持整体不变。常见例子包括 sulfate SO₄²⁻（硫酸根）、nitrate NO₃⁻（硝酸根）、carbonate CO₃²⁻（碳酸根）、ammonium NH₄⁺（铵根）和 hydroxide OH⁻（氢氧根）。
When naming a compound containing a polyatomic ion, keep the ion name unchanged. Na₂SO₄ is sodium sulfate, CaCO₃ is calcium carbonate, and NH₄Cl is ammonium chloride.
命名含多原子离子的化合物时，保留该离子名称不变。Na₂SO₄ 为 sodium sulfate（硫酸钠），CaCO₃ 为 calcium carbonate（碳酸钙），NH₄Cl 为 ammonium chloride（氯化铵）。
Use brackets when more than one polyatomic ion is needed in a formula. Calcium nitrate is Ca(NO₃)₂, not CaNO₃₂.
当化学式中需要多个多原子离子时，应使用括号。硝酸钙写作 Ca(NO₃)₂，而不是 CaNO₃₂。
| Formula | Name | 中文 |
|---|---|---|
| NO₃⁻ | nitrate | 硝酸根 |
| NO₂⁻ | nitrite | 亚硝酸根 |
| SO₄²⁻ | sulfate | 硫酸根 |
| SO₃²⁻ | sulfite | 亚硫酸根 |
| CO₃²⁻ | carbonate | 碳酸根 |
| HCO₃⁻ | hydrogencarbonate | 碳酸氢根 |
| OH⁻ | hydroxide | 氢氧根 |
| NH₄⁺ | ammonium | 铵根 |
The ion MnO₄⁻ is often called permanganate, but Cambridge A Level frequently uses manganate(VII). Both names describe the same ion, with manganese in the +7 oxidation state.
MnO₄⁻ 常被称作 permanganate（高锰酸根），但剑桥 A Level 通常称之为 manganate(VII)（高锰酸根）。两个名称描述同一种离子，锰处于 +7 氧化态。
5. Binary Covalent Compounds | 二元共价化合物
For non-metal–non-metal compounds, the more electropositive element is named first and the more electronegative element takes the -ide suffix. Greek prefixes indicate the number of atoms: mono-, di-, tri-, tetra-, penta- and hexa-.
对于非金属与非金属形成的化合物，电正性较强的元素先命名，电负性较强的元素词尾改为 -ide。希腊数字前缀表示原子个数：mono-、di-、tri-、tetra-、penta- 和 hexa-。
Examples include CO carbon monoxide, CO₂ carbon dioxide, PCl₅ phosphorus pentachloride and N₂O₄ dinitrogen tetroxide. The prefix mono- is usually omitted for the first element.
示例包括 CO carbon monoxide（一氧化碳）、CO₂ carbon dioxide（二氧化碳）、PCl₅ phosphorus pentachloride（五氯化磷）和 N₂O₄ dinitrogen tetroxide（四氧化二氮
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