📚 Reactivity of Metals | 金属的活动性
Why does sodium fizz violently in water while gold remains unchanged for thousands of years? The answer lies in the reactivity of metals. This article revises the Cambridge Lower Secondary Science topic on reactivity, including reactions of metals with oxygen, water and acids, the reactivity series, displacement reactions and metal extraction.
为什么钠遇水剧烈反应，而黄金数千年不变？答案在于金属的活动性。本文复习剑桥初中科学中“金属活动性”专题，包括金属与氧气、水和酸的反应、活动性顺序、置换反应以及金属冶炼。
1. Metals and Non-metals | 金属与非金属
Metals are found on the left side and in the centre of the Periodic Table, while non-metals are located on the right side. Most elements are metals. Common examples include iron, copper, aluminium, zinc, sodium and gold. Non-metals include oxygen, carbon, sulfur and chlorine.
金属位于元素周期表的左侧和中部，非金属位于右侧。大多数元素是金属。常见的金属有铁、铜、铝、锌、钠和金。非金属包括氧、碳、硫和氯。
Metals and non-metals have very different physical and chemical properties. Knowing these differences helps predict how an element will behave in a reaction.
金属和非金属的物理性质与化学性质差异很大。了解这些差异有助于预测元素在反应中的表现。
2. Physical Properties of Metals | 金属的物理性质
Metals are usually shiny when polished, malleable and ductile. They are good conductors of heat and electricity. Most metals have high melting points and boiling points, and they are solid at room temperature except mercury, which is a liquid.
金属通常在抛光后有光泽，具有延展性和可塑性。它们是良好的导热体和导电体。大多数金属的熔点和沸点较高，在室温下为固体，但汞除外，它是液体。
These properties can be used to distinguish metals from non-metals. For example, graphite, a form of carbon, conducts electricity, but it is not shiny or malleable like a metal.
这些性质可用于区分金属和非金属。例如，石墨是碳的一种形式，虽然能导电，但它不像金属那样有光泽或具有延展性。
3. Chemical Properties: Basic Ideas | 化学性质：基本概念
In chemical reactions, metals tend to lose electrons and form positive ions. This is why metals are often written as positive ions such as Na⁺, Mg²⁺ and Al³⁺ in compounds.
在化学反应中，金属倾向于失去电子形成阳离子。因此金属在化合物中通常以阳离子形式存在，如 Na⁺、Mg²⁺ 和 Al³⁺。
A reactive metal loses electrons more easily than a less reactive metal. Oxidation is gain of oxygen or loss of electrons. Reduction is loss of oxygen or gain of electrons. These terms help explain displacement and extraction reactions.
活动性较强的金属比活动性较弱的金属更容易失去电子。氧化是指得到氧或失去电子；还原是指失去氧或得到电子。这些术语有助于解释置换反应和金属冶炼反应。
4. Reaction with Oxygen | 与氧气的反应
Many metals react with oxygen when heated, forming metal oxides. Magnesium burns with a bright white flame to form white magnesium oxide.
许多金属在加热时与氧气反应，生成金属氧化物。镁在氧气中燃烧发出耀眼白光，生成白色氧化镁。
2Mg + O₂ → 2MgO
Sodium reacts with oxygen to form sodium oxide. Potassium and calcium also burn vigorously. Copper reacts slowly with oxygen, forming black copper(II) oxide.
钠与氧气反应生成氧化钠。钾和钙也能剧烈燃烧。铜与氧气反应较慢，生成黑色氧化铜。
4Na + O₂ → 2Na₂O
5. Reaction with Water | 与水的反应
Very reactive metals such as potassium, sodium and calcium react with cold water. Potassium reacts violently, sodium fizzes and moves on the surface, and calcium fizzes less vigorously. Hydrogen gas is released, and an alkaline metal hydroxide is formed.
钾、钠、钙等非常活泼的金属能与冷水反应。钾反应剧烈，钠在水面上发出嘶嘶声并游动，钙反应较为温和。反应放出氢气，并生成碱性金属氢氧化物。
2K + 2H₂O → 2KOH + H₂
Magnesium reacts very slowly with cold water but reacts vigorously with steam to form magnesium oxide and hydrogen. Zinc and iron react with steam but not with cold water.
镁与冷水反应很慢，但与水蒸气剧烈反应，生成氧化镁和氢气。锌和铁能与水蒸气反应，但不能与冷水反应。
Mg + H₂O (steam) → MgO + H₂
Copper, silver and gold do not react with water at all. This shows they are much less reactive.
铜、银和金完全不能与水反应。这说明它们的活动性要低得多。
6. Reaction with Acids | 与酸的反应
Metals above hydrogen in the reactivity series react with dilute acids to produce a salt and hydrogen gas. The general word equation is:
活动性顺序中位于氢以上的金属能与稀酸反应，生成盐和氢气。一般文字表达式为：
metal + acid → salt + hydrogen
For example, magnesium reacts with dilute hydrochloric acid to form magnesium chloride and hydrogen:
例如，镁与稀盐酸反应生成氯化镁和氢气：
Mg + 2HCl → MgCl₂ + H₂
Hydrogen gas is tested with a lighted splint, which gives a squeaky pop. Copper, silver and gold do not react with dilute acids because they are below hydrogen in the reactivity series.
氢气可用点燃的木条检验，木条会发出“噗”的一声。铜、银和金不能与稀酸反应，因为它们在活动性顺序中位于氢以下。
7. The Reactivity Series | 活动性顺序
The reactivity series lists metals in order of their tendency to react. The order from most reactive to least reactive is:
活动性顺序将金属按反应倾向排列。从最活泼到最不活泼的顺序是：
K > Na > Ca > Mg > Al > (C) > Zn > Fe > (H) > Cu > Ag > Au
Carbon and hydrogen are included as reference points because they are used in metal extraction and acid reactions.
碳和氢被列为参照点，因为它们用于金属冶炼和酸反应中。
| Metal | Reaction with cold water | Reaction with dilute acid |
|---|---|---|
| Potassium | Violent | Explosive |
| Sodium | Vigorous | Very fast |
| Calcium | Moderate | Fast |
| Magnesium | Very slow | Fast |
| Zinc | Steam only | Moderate |
| Iron | Steam only | Slow |
| Copper | No reaction | No reaction |
8. Displacement Reactions | 置换反应
A more reactive metal can displace a less reactive metal from its compound. For example, zinc displaces copper from copper(II) sulfate solution because zinc is more reactive than copper.
活动性较强的金属能将活动性较弱的金属从其化合物中置换出来。例如，锌能将铜从硫酸铜溶液中置换出来，因为锌比铜更活泼。
Zn + CuSO₄ → ZnSO₄ + Cu
The blue colour of copper(II) sulfate solution fades, and a reddish-brown deposit of copper forms on the zinc. This is a redox reaction: zinc is oxidised, and copper(II) ions are reduced.
硫酸铜溶液的蓝色逐渐变浅，锌表面生成红棕色铜沉积物。这是一个氧化还原反应：锌被氧化，铜离子被还原。
Zn → Zn²⁺ + 2e⁻ and Cu²⁺ + 2e⁻ → Cu
9. Carbon and Hydrogen as Reducing Agents | 碳和氢作为还原剂
Carbon is a non-metal, but it is included in the reactivity series because carbon can remove oxygen from metal oxides of metals below it. This process is called reduction.
碳是非金属，但活动性顺序中包括碳，因为碳能从比它不活泼的金属氧化物中脱去氧。这个过程称为还原。
2CuO + C → 2Cu + CO₂
Hydrogen can also reduce some metal oxides. For example, hydrogen reduces copper(II) oxide to copper and water.
氢气也能还原某些金属氧化物。例如，氢气将氧化铜还原为铜和水。
CuO + H₂ → Cu + H₂O
10. Extraction of Metals | 金属的冶炼
The method used to extract a metal from its ore depends on its position in the reactivity series. Very reactive metals such as potassium, sodium, calcium and aluminium are extracted by electrolysis of their molten compounds.
从矿石中提取金属的方法取决于金属在活动性顺序中的位置。钾、钠、钙和铝等非常活泼的金属通过电解其熔融化合物提取。
Metals in the middle of the series, such as zinc and iron, are usually extracted by heating their oxides with carbon. Carbon acts as a reducing agent. For example, iron is extracted from iron(III) oxide in a blast furnace using carbon monoxide.
活动性位于中间的金属，如锌和铁，通常用碳还原其氧化物来提取。碳作为还原剂。例如，铁在高炉中用一氧化碳从氧化铁中还原出来。
Fe₂O₃ + 3CO → 2Fe + 3CO₂
Unreactive metals such as gold and silver are found as uncombined elements in nature, so no chemical extraction is needed.
不活泼的金属如金和银在自然界中以单质形式存在，因此不需要化学提取。
11. Exam Tips and Common Errors | 考试技巧与常见错误
When testing hydrogen, do not say the hydrogen burns with a squeaky pop. Say that a lighted splint held over the mouth of the test tube gives a squeaky pop. Always write states or clear observations where asked.
检验氢气时，不要说氢气燃烧发出“噗”声。应该说：将点燃的木条放在试管口，听到“噗”的一声。如果题目要求，要写出状态或清晰的实验现象。
Learn the reactivity series accurately. Many students confuse aluminium and magnesium. Remember that aluminium is more reactive than zinc but less reactive than magnesium. Carbon is placed between aluminium and zinc.
要准确记忆活动性顺序。许多学生混淆铝和镁。请记住，铝比锌活泼，但不如镁活泼。碳位于铝和锌之间。
When writing displacement equations, check that the metal alone is more reactive than the metal in the compound. If there is no displacement, simply write no reaction.
书写置换反应方程式时，要确认单质金属比化合物中的金属更活泼。如果没有置换发生，就写“无反应”。
12. Summary | 总结
Metals react with oxygen, water and acids at different rates. The reactivity series arranges metals from potassium to gold. More reactive metals displace less reactive metals from solutions, and carbon or hydrogen can reduce metal oxides of less reactive metals.
金属与氧气、水和酸的反应速率不同。活动性顺序将金属从钾到金排列。较活泼的金属能从溶液中置换出较不活泼的金属，碳或氢可以还原较不活泼金属的氧化物。
Extraction methods depend on reactivity: electrolysis for very reactive metals, carbon reduction for middle metals, and native occurrence for unreactive metals. Master these ideas and equations to succeed in the Cambridge Science checkpoint.
金属冶炼方法取决于活动性：活泼金属用电解，中等活动性金属用碳还原，不活泼金属以单质存在。掌握这些概念和方程式，才能在剑桥科学考试中取得成功。
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