📚 Atomic Structure and Elements | 原子与元素 考点精讲
In IGCSE AQA Science, the concepts of atoms and elements form the bedrock of chemistry. You must be able to describe the structure of an atom, explain the arrangement of electrons, and relate this to the periodic table and ion formation.
在 IGCSE AQA 科学中，原子和元素的概念是化学的基石。你必须能够描述原子的结构、解释电子的排列方式，并将其与元素周期表和离子形成联系起来。
1. What is an Atom? | 什么是原子？
An atom is the smallest particle of an element that can exist and still retain the chemical properties of that element. All substances are made of atoms, either combined or on their own.
原子是元素能够存在的最小粒子，并且仍保持该元素的化学性质。所有物质都是由原子构成的，无论是结合状态还是单独存在。
Atoms contain a dense central nucleus surrounded by negatively charged electrons moving in shells. The nucleus itself contains two types of particles: protons and neutrons.
原子包含一个致密的中心原子核，原子核周围是带负电荷的电子，在电子层中运动。原子核本身包含两种粒子：质子和中子。
2. Subatomic Particles | 亚原子粒子
There are three subatomic particles you need to know: protons, neutrons and electrons. Protons have a relative mass of 1 and a positive charge (+1). Neutrons also have a relative mass of 1 but carry no charge (0). Electrons have a relative mass of only 1/1836 and a negative charge (–1).
你需要知道三种亚原子粒子：质子、中子和电子。质子的相对质量为 1，带一个正电荷；中子的相对质量也是 1，但不带电荷；电子的相对质量仅为 1/1836，带一个负电荷。
Virtually all of the mass of an atom is concentrated in the nucleus because protons and neutrons are much heavier than electrons. The charge of the nucleus is positive and equal to the number of protons.
几乎原子的全部质量都集中在原子核上，因为质子和中子比电子重得多。原子核带正电，电荷量等于质子数。
3. Atomic Number and Mass Number | 原子序数与质量数
The atomic number (Z) is the number of protons in an atom. It is unique to each element and determines the element's identity. In a neutral atom, the number of electrons is exactly equal to the number of protons.
原子序数（Z）是原子中质子的数目，每种元素都有独特的原子序数，决定了元素的种类。在电中性原子中，电子数恰好等于质子数。
The mass number (A) is the sum of protons and neutrons in the nucleus. We often show the mass number and atomic number alongside the symbol: ᴀ₂X, for example carbon-12 is ¹²₆C.
质量数（A）是原子核中质子数与中子数之和。我们常将质量数和原子序数标在元素符号旁：ᴀ₂X，例如碳-12 表示为 ¹²₆C。
the number of neutrons by subtracting the atomic number from the mass number: Neutrons = A – Z.
根据这种表示法，你可以用质量数减去原子序数得到中子数：中子数 = A – Z。
4. Isotopes | 同位素
Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. As a result, they have the same atomic number but different mass numbers.
同位素是同一元素的原子，它们有相同的质子数但中子数不同。因此，它们的原子序数相同，但质量数不同。
For example, carbon exists as two stable isotopes: ¹²₆C (6 protons, 6 neutrons) and ¹⁴₆C (6 protons, 8 neutrons). Both behave chemically identically because they have the same electron arrangement.
例如，碳有两种稳定同位素：¹²₆C（6 个质子，6 个中子）和 ¹⁴₆C（6 个质子，8 个中子）。两者的化学性质相同，因为它们具有相同的电子排布。
5. Relative Atomic Mass (Aᵣ) | 相对原子质量
The relative atomic mass (Aᵣ) is the average mass of all the isotopes of an element, taking into account the percentage abundance of each isotope. It is based on the carbon-12 scale, where ¹²₆C is assigned a mass of exactly 12.
相对原子质量（Aᵣ）是元素所有同位素质量的平均值，并考虑了每种同位素的丰度百分比。它基于碳-12 标准，¹²₆C 的质量被定为精确的 12。
Aᵣ = (isotopic mass₁ × %abundance₁ + isotopic mass₂ × %abundance₂ + …) ÷ 100
计算示例：氯有两种稳定同位素：³⁵Cl（75%）和 ³⁷Cl（25%）。相对原子质量 Aᵣ = (35 × 75 + 37 × 25) ÷ 100 = 35.5。
A worked example: chlorine has two stable isotopes: ³⁵Cl (75%) and ³⁷Cl (25%). Its relative atomic mass Aᵣ = (35 × 75 + 37 × 25) ÷ 100 = 35.5.
6. Electron Shells and Electronic Configuration | 电子层与电子排布
Electrons are arranged in shells (energy levels) around the nucleus. For the first 20 elements, the first shell can hold up to 2 electrons, the second up to 8, and the third up to 8.
电子排列在原子核外的电子层（能级）中。对于前 20 号元素，第一电子层最多容纳 2 个电子，第二层最多 8 个，第三层最多 8 个。
The electronic configuration shows how many electrons occupy each shell. For instance, sodium (Na) has an atomic number of 11, so its configuration is 2,8,1. Calcium (Ca) with atomic number 20 is 2,8,8,2.
电子排布展示了每个电子层有多少电子。例如，钠（Na）的原子序数为 11，其电子排布为 2,8,1。钙（Ca）的原子序数为 20，排布为 2,8,8,2。
7. The Periodic Table and Electron Shells | 元素周期表与电子层
The modern periodic table arranges elements in order of increasing atomic number. The group number (vertical column) tells you how many electrons are in the outer shell for the main groups. For example, Group 1 elements all have one outer electron; Group 7 elements have seven.
现代元素周期表按原子序数递增排列。主族元素的族号（纵列）告诉你最外层有多少个电子。例如，第 1 族元素最外层都有 1 个电子；第 7 族元素都有 7 个电子。
The period number (horizontal row) matches the number of occupied electron shells. Elements in Period 2 have electrons in two shells, Period 3 elements have three shells, and so on.
周期数（横行）等于已占据的电子层数。第 2 周期的元素电子占据两层，第 3 周期元素占据三层，依此类推。
This means that elements in the same group have similar chemical properties because their outer-shell electrons determine how they react.
这意味着同族元素具有相似的化学性质，因为它们的化学反应由外层电子决定。
8. Noble Gases – Stable Electron Arrangements | 稀有气体 – 稳定电子排布
Noble gases (Group 0 or 8) have full outer shells, which makes them exceptionally stable and unreactive. Helium has a full first shell with 2 electrons. Neon has the configuration 2,8; argon is 2,8,8.
稀有气体（0 族或 8 族）具有全满的外电子层，这使得它们异常稳定且不活泼。氦的第一层填满 2 个电子；氖的排布为 2,8；氩为 2,8,8。
When other atoms react, they tend to lose, gain or share electrons to achieve a noble gas electron configuration – often referred to as the 'octet rule' for eight outer electrons (or two for hydrogen and lithium).
其他原子发生反应时，倾向于失去、得到或共用电子以达到稀有气体的电子构型——通常称为“八隅规则”（外层 8 个电子，氢和锂则为 2 个电子）。
9. Ions: Formation by Gaining or Losing Electrons | 离子：电子的得失
When an atom loses electrons, it becomes a positive ion (cation) because it now has more protons than electrons. When an atom gains electrons, it becomes a negative ion (anion).
原子失去电子后变成正离子（阳离子），因为它现在的质子数多于电子数。原子得到电子后变成负离子（阴离子）。
Example: sodium atom (2,8,1) loses one electron to form Na⁺ with configuration 2,8, achieving the stability of neon. Chlorine atom (2,8,7) gains one electron to form Cl⁻ with configuration 2,8,8, like argon.
示例：钠原子（2,8,1）失去一个电子形成 Na⁺，排布为 2,8，达到了氖的稳定结构。氯原子（2,8,7）得到一个电子形成 Cl⁻，排布为 2,8,8，像氩一样。
ge on an ion can be predicted from the group number: Group 1 → +1, Group 2 → +2, Group 6 → –2, Group 7 → –1.
金属通常失去电子形成阳离子，非金属得到电子形成阴离子。离子所带电荷可通过族号预测：第 1 族 → +1，第 2 族 → +2，第 6 族 → –2，第 7 族 → –1。
10. Elements, Compounds and Mixtures | 元素、化合物与混合物
An element is a substance made from only one type of atom. About 118 elements are known and are listed on the periodic table. A compound contains two or more different elements chemically combined in fixed proportions.
元素是由同一种原子组成的物质。已知约有 118 种元素，列于元素周期表中。化合物含有两种或多种不同元素，它们以固定的比例通过化学方式结合。
A mixture consists of two or more substances (elements or compounds) that are not chemically bonded. Mixtures can be separated by physical means such as filtration or distillation, whereas compounds require chemical reactions to break the bonds.
混合物由两种或多种物质（元素或化合物）组成，它们之间没有化学键合。混合物可以通过过滤或蒸馏等物理方法分离，而化合物则需要化学反应来断开化学键。
In your IGCSE exam, you should be able to classify substances into these categories and recognise their differences in properties.
在 IGCSE 考试中，你应能够将物质分类到这些类别中，并识别它们在性质上的差异。
Published by TutorHao | Science Revision Series | aleveler.com
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