📚 Chlorides: From Table Salt to Silver Chloride | 氯化物：从食盐到氯化银
Chlorides are a large and important family of chemical compounds. They all contain chlorine, but not as the toxic green gas Cl₂; instead, chlorine is present as the chloride ion, Cl⁻. In this article, you will learn how chlorides form, how to name them, how to test for them, and why compounds such as sodium chloride and hydrogen chloride matter in everyday life.
氯化物是一个庞大而重要的化合物家族。它们都含有氯，但并不是以有毒的绿色气体 Cl₂ 形式存在；相反，氯以氯离子 Cl⁻ 的形式存在。在本文中，你将学习氯化物如何形成、如何命名、如何检验它们，以及氯化钠和氯化氢等化合物为何在日常生活中如此重要。
1. What Are Chlorides? | 什么是氯化物？
A chloride is a compound that contains the chloride ion, Cl⁻. The chloride ion forms when a chlorine atom gains one electron. Because it has gained a negative charge, it is an anion.
氯化物是含有氯离子 Cl⁻ 的化合物。氯离子是氯原子得到一个电子后形成的。由于它带上了负电荷，因此是一种阴离子。
Many chlorides are salts made from a metal and chlorine. For example, sodium chloride, NaCl, contains sodium ions Na⁺ and chloride ions Cl⁻.
许多氯化物是由金属和氯形成的盐。例如，氯化钠 NaCl 含有钠离子 Na⁺ 和氯离子 Cl⁻。
Some chlorides are covalent molecules, such as hydrogen chloride, HCl. So chlorides are not all ionic; their bonding depends on the element joined to chlorine.
有些氯化物是共价分子，例如氯化氢 HCl。因此，并不是所有氯化物都是离子化合物；它们的成键方式取决于与氯结合的元素。
2. The Chloride Ion | 氯离子
The chloride ion has the formula Cl⁻. It has 17 protons but 18 electrons, so its overall charge is 1−.
氯离子的化学符号为 Cl⁻。它有 17 个质子但有 18 个电子，因此整体带 1 个负电荷。
Because chloride ions are negative, they are attracted to positive ions in ionic compounds. This electrostatic attraction holds the ionic lattice together.
由于氯离子带负电，它们在离子化合物中会被正离子吸引。这种静电吸引力将离子晶格结合在一起。
Chloride ions are stable. They have the same electron arrangement as the noble gas argon, which makes them much less reactive than chlorine atoms.
氯离子很稳定。它们具有与稀有气体氩相同的电子排布，因此比氯原子反应性弱得多。
3. Naming Chlorides | 氯化物的命名
The name of a chloride usually comes from the metal or positive ion followed by the word ‘chloride’. Sodium forms sodium chloride, potassium forms potassium chloride, and calcium forms calcium chloride.
氯化物的名称通常来自金属或正离子，后面加上“氯化”二字。钠形成氯化钠，钾形成氯化钾，钙形成氯化钙。
If a metal can form more than one ion, we use Roman numerals. For example, iron(II) chloride contains Fe²⁺ and iron(III) chloride contains Fe³⁺.
如果一种金属可以形成不止一种离子，我们就使用罗马数字。例如，氯化亚铁含 Fe²⁺，氯化铁含 Fe³⁺。
For covalent chlorides, simple prefixes are used: HCl is hydrogen chloride, CCl₄ is carbon tetrachloride. KS3 usually focuses on naming simple metal chlorides.
对于共价氯化物，使用简单的前缀命名：HCl 是氯化氢，CCl₄ 是四氯化碳。KS3 阶段通常主要学习简单金属氯化物的命名。
4. Sodium Chloride: The Most Familiar Chloride | 氯化钠：最常见的氯化物
Sodium chloride, NaCl, is ordinary table salt. It is an ionic compound made of Na⁺ and Cl⁻ ions arranged in a giant lattice.
氯化钠 NaCl 就是普通的食盐。它是一种离子化合物，由 Na⁺ 和 Cl⁻ 离子排列成巨型晶格。
It dissolves easily in water, forming a neutral solution. The dissolved ions can carry electric current, so sodium chloride solution conducts electricity.
它易溶于水，形成中性溶液。溶解后的离子能够导电，因此氯化钠溶液可以导电。
Sodium chloride is essential for life. It helps control water balance in the body and is used to flavour and preserve food.
氯化钠对生命至关重要。它有助于控制体内的水分平衡，并用于调味和保存食物。
5. Hydrogen Chloride and Hydrochloric Acid | 氯化氢与盐酸
Hydrogen chloride, HCl, is a colourless gas at room temperature. It is a covalent molecule, not an ionic salt.
氯化氢 HCl 在室温下是一种无色气体。它是共价分子，不是离子盐。
When hydrogen chloride dissolves in water, it forms hydrochloric acid. The solution contains H⁺ ions and Cl⁻ ions, and it is strongly acidic.
当氯化氢溶于水时，形成盐酸。该溶液含有 H⁺ 离子和 Cl⁻ 离子，呈强酸性。
Hydrochloric acid is found in the stomach, where it helps digest food and kills harmful bacteria. In the laboratory, it is a common strong acid used to make chlorides.
胃液中含有盐酸，它有助于消化食物并杀死有害细菌。在实验室中，盐酸是一种常用于制备氯化物的强酸。
6. Other Important Chlorides | 其他重要氯化物
Calcium chloride, CaCl₂, is used to melt ice on roads because it lowers the freezing point of water. It is also used as a drying agent.
氯化钙 CaCl₂ 用于融化道路上的冰，因为它能降低水的凝固点。它也可用作干燥剂。
Potassium chloride, KCl, is used in fertilisers as a source of potassium for plants. It is also used as a salt substitute in low-sodium foods.
氯化钾 KCl 在化肥中用作植物的钾来源。它也用作低钠食品中的食盐替代品。
Magnesium chloride, MgCl₂, is found in sea water and is used in dust control and as a mineral supplement. Silver chloride, AgCl, is important in photography and testing.
氯化镁 MgCl₂ 存在于海水中，用于控制扬尘和作为矿物质补充剂。氯化银 AgCl 在摄影和检验中很重要。
7. Physical Properties of Chlorides | 氯化物的物理性质
Metal chlorides are usually crystalline solids at room temperature. They have high melting points because the ionic bonds in the lattice are strong.
金属氯化物在室温下通常是晶体固体。它们的熔点较高，因为晶格中的离子键很强。
Many metal chlorides dissolve in water to form clear solutions. The solutions often conduct electricity because they contain mobile ions.
许多金属氯化物溶于水形成透明溶液。这些溶液通常能导电，因为它们含有可自由移动的离子。
Covalent chlorides such as hydrogen chloride have low melting and boiling points. They may be gases or volatile liquids at room temperature.
共价氯化物（如氯化氢）的熔点和沸点较低。它们在室温下可能是气体或易挥发的液体。
8. Chemical Reactions That Make Chlorides | 生成氯化物的化学反应
Chlorides can be made when a metal reacts with hydrochloric acid. For example, magnesium reacts with hydrochloric acid to produce magnesium chloride and hydrogen gas.
金属与盐酸反应可以生成氯化物。例如，镁与盐酸反应生成氯化镁和氢气。
A general word equation is: metal + hydrochloric acid → metal chloride + hydrogen. In symbols for magnesium:
一般文字方程式为：金属 + 盐酸 → 金属氯化物 + 氢气。用符号表示镁的反应：
Mg + 2HCl → MgCl₂ + H₂
Chlorides can also form when a metal burns in chlorine gas. Sodium burns in chlorine to form sodium chloride:
金属在氯气中燃烧也可以生成氯化物。钠在氯气中燃烧生成氯化钠：
2Na + Cl₂ → 2NaCl
Neutralisation between hydrochloric acid and a base also produces a chloride salt and water:
盐酸与碱的中和反应也会生成氯化物盐和水：
NaOH + HCl → NaCl + H₂O
9. Testing for Chloride Ions | 氯离子的检验
To test for chloride ions in a solution, add a few drops of dilute nitric acid, then add silver nitrate solution. A white precipitate of silver chloride forms if chloride ions are present.
要检验溶液中的氯离子，先滴加几滴稀硝酸，然后加入硝酸银溶液。如果存在氯离子，就会生成氯化银的白色沉淀。
The ionic equation is:
离子方程式为：
Ag⁺(aq) + Cl⁻(aq) → AgCl(s)
The white solid is silver chloride.
白色固体就是氯化银。
Silver chloride is insoluble in water and does not dissolve in dilute nitric acid. This confirms the precipitate is a chloride, not a carbonate.
氯化银不溶于水，也不溶于稀硝酸。这可以确认沉淀是氯化物，而不是碳酸盐。
In contrast, carbonate ions also give a white precipitate with silver nitrate, but that precipitate dissolves in nitric acid. So the acid step is important.
相比之下，碳酸根离子与硝酸银也会产生白色沉淀，但该沉淀会溶于硝酸。因此加酸的步骤很重要。
10. Uses of Chlorides and Safety Notes | 氯化物的用途与安全注意事项
Chlorides have many uses: table salt for food, calcium chloride for de-icing, potassium chloride for fertilisers, and hydrochloric acid for cleaning and digestion.
氯化物用途广泛：食盐用于食品，氯化钙用于除冰，氯化钾用于化肥，盐酸用于清洁和消化。
Most common chlorides such as sodium chloride are safe in normal amounts. However, some chlorides can be harmful if swallowed in large quantities, and hydrochloric acid is corrosive.
大多数常见氯化物（如氯化钠）在正常用量下是安全的。但有些氯化物如果大量吞食可能有害，盐酸具有腐蚀性。
Always wear eye protection when using acids or silver nitrate in the laboratory. Wash spills off skin with plenty of water and follow your teacher’s safety instructions.
在实验室使用酸或硝酸银时，务必佩戴护目镜。皮肤上的溅洒物要用大量水冲洗，并遵守老师的安全指导。
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