📚 Elements and Their Symbols | 元素及其符号
Everything around you is built from tiny building blocks called elements. Learning element names and symbols is the first step to reading and writing the language of chemistry.
你周围的一切都是由称为元素的小积木组成的。学习元素的名称和符号是阅读和书写化学语言的第一步。
1. What Is an Element? | 什么是元素？
An element is a pure substance that contains only one type of atom. It cannot be broken down into anything simpler by chemical reactions. For example, a piece of pure gold contains only gold atoms.
元素是只含一种原子的纯净物。它不能通过化学反应分解成更简单的物质。例如，一块纯金只含金原子。
Elements are the basic ingredients of all matter. Water is not an element because it can be split into hydrogen and oxygen, but hydrogen and oxygen are elements.
元素是所有物质的基本成分。水不是元素，因为它可以分解成氢和氧，但氢和氧是元素。
At room temperature, different elements can be solids, liquids or gases. Iron is a solid, oxygen is a gas, and mercury is a liquid metal.
在室温下，不同的元素可以是固体、液体或气体。铁是固体，氧气是气体，汞是液态金属。
2. Atoms and Elements | 原子与元素
Every element is made of atoms. An atom is the smallest particle of an element that still behaves as that element. Iron is made of iron atoms, and copper is made of copper atoms.
每种元素由原子构成。原子是元素中仍保持该元素性质的最小粒子。铁由铁原子构成，铜由铜原子构成。
Atoms of one element are all the same type, but atoms of different elements have different properties. This is why oxygen gas feels very different from solid carbon.
同一种元素的原子都是相同类型，但不同元素的原子具有不同性质。这就是为什么氧气与固态碳感觉非常不同。
When atoms of the same element join together, they can form molecules. Oxygen gas in the air is made of O₂ molecules, each containing two oxygen atoms.
当同种元素的原子结合时，它们可以形成分子。空气中的氧气由 O₂ 分子组成，每个分子含两个氧原子。
3. What Is a Chemical Symbol? | 什么是化学符号？
A chemical symbol is a short code used by scientists to represent an element. It is usually taken from the element’s English name, such as H for hydrogen and O for oxygen.
化学符号是科学家用来表示元素的简短代码。它通常取自元素的英文名称，例如 H 代表氢，O 代表氧。
Using symbols saves time. Instead of writing ‘one atom of oxygen joined to two atoms of hydrogen’, chemists write H₂O.
使用符号可以节省时间。化学家不用写“一个氧原子与两个氢原子结合”，而是写 H₂O。
Chemical symbols are used internationally, so scientists from different countries can understand the same formula without translating the full names.
化学符号在国际上通用，因此来自不同国家的科学家无需翻译全名就能理解同一个化学式。
4. Rules for Writing Element Symbols | 书写元素符号的规则
The first letter of a chemical symbol must always be a capital letter. If there is a second letter, it must always be lowercase. For example, helium is He, not HE or he.
化学符号的第一个字母必须始终大写。如果有第二个字母，它必须始终小写。例如，氦是 He，而不是 HE 或 he。
This rule is important because capitalisation can change meaning. Co is cobalt, but CO is the compound carbon monoxide. In chemistry, ‘Co’ and ‘CO’ are completely different substances.
这条规则很重要，因为大小写会改变含义。Co 是钴，而 CO 是化合物一氧化碳。在化学中，“Co”和“CO”是完全不同的物质。
One-letter symbols are also capitalised: carbon is C, nitrogen is N, and sulfur is S. Always check your writing to make sure the second letter is small.
单字母符号也要大写：碳是 C，氮是 N，硫是 S。书写后要检查，确保第二个字母小写。
5. Common Elements and Their Symbols | 常见元素及其符号
KS3 students should recognise the symbols of common elements. The table below lists some of the most useful ones for school chemistry.
KS3 学生应认识常见元素的符号。下表列出了一些对学校化学最有用的元素符号。
| Hydrogen | 氢 | H | Helium |
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