📚 Atomic Structure and the Periodic Table | 原子结构与元素周期表
Understanding the atom is the foundation of all chemistry. In the Edexcel IGCSE Science specification, you need to know the structure of atoms, how electrons are arranged, and how this arrangement determines the position of elements in the Periodic Table. This revision guide covers every key idea you need for your exam.
理解原子是所有化学的基础。在 Edexcel IGCSE 科学考纲中，你需要知道原子的结构、电子的排布方式，以及这种排布如何决定元素在周期表中的位置。本复习指南涵盖你考试所需的每一个关键知识点。
1. Atoms: Basic Particles | 原子：基本粒子
An atom is the smallest unit of an element that can take part in a chemical reaction. It consists of three subatomic particles: protons, neutrons and electrons. Protons are positively charged, neutrons have no charge, and electrons are negatively charged.
原子是元素中能参与化学反应的最小单位。它由三种亚原子粒子组成：质子、中子和电子。质子带正电荷，中子不带电荷，电子带负电荷。
Protons and neutrons are located in the nucleus. They have roughly equal mass (1 unit each).
质子和中子位于原子核中，它们质量大致相等（每个约1个质量单位）。
Electrons move around the nucleus in energy levels (shells). They are very small and have almost no mass.
电子在核外能量层（电子层）中运动。它们非常小，几乎可以忽略不计质量。
The nucleus is small and dense compared with the whole atom.
与整个原子相比，原子核体积小但密度极高。
Proton: charge +1, mass 1
Neutron: charge 0, mass 1
Electron: charge −1, mass 1/1836
In a neutral atom, the number of electrons equals the number of protons. Therefore the total positive charge balances the total negative charge.
在中性原子中，电子数等于质子数。因此总正电荷与总负电荷相互抵消。
2. Atomic Number and Mass Number | 原子序数和质量数
The atomic number (Z) is the number of protons in the nucleus of an atom. It is also called the proton number. The mass number (A) is the total number of protons and neutrons in the nucleus.
原子序数（Z）是原子核中的质子数，也称为质子数。质量数（A）是原子核中质子数和中子数的总和。
Atomic number defines the element. If the number of protons changes, the element changes.
原子序数决定了元素种类。如果质子数改变，元素就改变。
The number of neutrons can be found using: neutrons = mass number − atomic number.
中子数可以通过以下公式计算：中子数 = 质量数 − 原子序数。
For example, a sodium atom has atomic number 11 and mass number 23. It has 11 protons, 11 electrons and 12 neutrons.
例如，钠原子的原子序数为11，质量数为23。它有11个质子、11个电子和12个中子。
⁴⁰₁₈Ar means an argon atom with atomic number 18 and mass number 40.
在科学表示法中，左上角为质量数，左下角为原子序数。例如 ⁴⁰₁₈Ar 表示原子序数为18、质量数为40的氩原子。
3. Isotopes | 同位素
Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. Since the number of protons is the same, they have the same atomic number, but their mass numbers differ.
同位素是同一元素中具有相同质子数但不同中子数的原子。因为质子数相同，它们的原子序数相同，但质量数不同。
Isotopes of an element have identical chemical properties because chemical behaviour is determined by the electron arrangement.
同位素的化学性质完全相同，因为化学行为由电子排布决定。
Physical properties, such as mass or density, may be slightly different.
物理性质如质量或密度可能略有不同。
Chlorine has two common isotopes: ³⁵₁₇Cl and ³⁷₁₇Cl. This affects the relative atomic mass of chlorine (35.5).
氯有两种常见同位素：³⁵₁₇Cl 和 ³⁷₁₇Cl。这影响了氯的相对原子质量（35.5）。
You may be asked to interpret isotope notation or calculate relative atomic mass from isotope abundances.
考试中可能会要求你解读同位素符号，或根据同位素丰度计算相对原子质量。
4. Electronic Configuration | 电子排布
Electrons occupy energy levels (shells) around the nucleus. The first shell can hold up to 2 electrons, the second and third shells can each hold up to 8 electrons.
电子占据原子核周围的能量层（电子壳）。第一层最多容纳2个电子，第二层和第三层最多各容纳8个电子。
The lowest energy shell is filled first.
能量最低的壳层先被填充。
The electron configuration is written as numbers separated by dots or commas, e.g. sodium is 2.8.1.
电子排布用点号或逗号分隔的数字表示，例如钠是 2.8.1。
For the first 20 elements, you can work out the configuration using the rule 2, 8, 8.
对前20号元素，你可以使用2、8、8的规则推算出排布方式。
For example, oxygen (atomic number 8) has two electrons in the first shell and six in the second: 2.6.
例如，氧（原子序数8）的第一层有2个电子，第二层有6个：2.6。
The number of electrons in the outer shell determines the element's chemical reactivity.
最外层电子数决定了元素的化学活泼性。
5. The Periodic Table Layout | 周期表的布局
The Periodic Table arranges elements in order of increasing atomic number. The vertical columns are called groups and the horizontal rows are called periods.
周期表按原子序数递增的顺序排列元素。纵列称为族，横排称为周期。
Elements in the same group have the same number of outer-shell electrons.
同一族的元素具有相同的最外层电子数。
The group number equals the number of outer electrons for Groups 1–8 (except for transition metals).
对第1至8族（过渡金属除外），族号等于最外层电子数。
The period number tells you the number of occupied electron shells.
周期数告诉你该元素占据的电子层数量。
For example, magnesium is in Group 2 and Period 3, so it has 2 outer electrons and 3 shells.
例如，镁位于第2族和第3周期，因此它有2个外层电子和3个电子层。
Group number → outer electrons
Period number → number of shells
记住：族号对应最外层电子数，周期号对应电子层数。
6. Group 1: Alkali Metals | 第1族：碱金属
Group 1 elements are soft metals with one outer electron. They include lithium, sodium, potassium, rubidium and caesium. They are very reactive and are stored under oil to prevent reaction with air or moisture.
第1族元素是柔软金属，最外层只有1个电子。包括锂、钠、钾、铷和铯。它们非常活泼，需要存放在油中以隔绝空气和水分。
They react with water to form a metal hydroxide and hydrogen gas.
它们与水反应生成金属氢氧化物和氢气。
Reactivity increases down the group because the outer electron is further from the nucleus and is easier to lose.
从上到下活泼性增强，因为外层电子距离核越来越远，更容易失去。
They form ionic compounds with non-metals, losing the single outer electron to gain a +1 charge.
它们与非金属形成离子化合物，失去唯一的外层电子后带+1电荷。
2Na + 2H₂O → 2NaOH + H₂
金属钾与水反应更为剧烈，甚至能点燃产生的氢气。
7. Group 7: Halogens | 第7族：卤素
Group 7 elements are non-metals with seven outer electrons. They include fluorine, chlorine, bromine and iodine. They exist as diatomic molecules, meaning two atoms join together.
第7族元素是非金属，最外层有7个电子。包括氟、氯、溴和碘。它们以双原子分子形式存在，即两个原子结合在一起。
They form ionic compounds with metals by gaining one electron to form a −1 ion.
它们与金属形成离子化合物时，获得一个电子形成−1价的离子。
Reactivity decreases down the group because it becomes harder to gain an electron as the atom gets larger.
从上到下活泼性减弱，因为原子变大后更难获得电子。
A more reactive halogen can displace a less reactive halogen from its salt solution.
较活泼的卤素可以将其较不活泼的卤素从盐溶液中置换出来。
mple, chlorine displaces bromine from potassium bromide solution: Cl₂ + 2KBr → 2KCl + Br₂.
例如，氯能从溴化钾溶液中置换出溴：Cl₂ + 2KBr → 2KCl + Br₂。
8. Group 0: Noble Gases | 第0族：稀有气体
Group 0 elements are also called noble gases. They include helium, neon, argon, krypton and xenon. They have full outer shells of electrons (2 for helium, 8 for others), making them very stable and unreactive.
第0族元素也被称为稀有气体。包括氦、氖、氩、氪和氙。它们的最外层电子已经充满（氦为2个，其余为8个），因此非常稳定且不易反应。
They exist as single atoms (monatomic) because they have no tendency to bond.
它们以单个原子（单原子）形式存在，因为没有成键的倾向。
Their inertness makes them useful in lighting, welding and filling balloons.
它们的惰性使其在照明、焊接和充气球方面很有用。
The boiling points of noble gases increase as you go down the group.
稀有气体的沸点随原子序数增加而升高。
Because they already have a stable electronic configuration, noble gases do not normally form compounds.
由于稀有气体已经具有稳定的电子构型，它们通常不形成化合物。
9. Metals vs Non-Metals | 金属与非金属
The Periodic Table is divided into metals (on the left) and non-metals (on the right). The boundary runs diagonally from boron to tellurium.
周期表分为金属（左侧）和非金属（右侧）。分界线从硼到碲斜向延伸。
Metals tend to lose electrons and form positive ions; non-metals tend to gain electrons and form negative ions.
金属倾向于失去电子形成正离子；非金属倾向于获得电子形成负离子。
Metals are shiny, malleable, ductile and good conductors of heat and electricity. Non-metals are usually dull, brittle and poor conductors.
金属有光泽、可延展、可锻且导热导电良好。非金属通常暗淡、易碎且导电导热性差。
Transition metals (the central block) have variable oxidation states and often form coloured compounds.
过渡金属（中间区块）具有可变化合价，且常形成有色化合物。
You should be able to deduce whether an element is a metal or non-metal from its position in the Periodic Table.
你应该能根据元素在周期表中的位置判断它是金属还是非金属。
10. Trends in Reactivity | 反应活泼性的趋势
In Groups 1 and 2, reactivity increases down the group. In Groups 6 and 7, reactivity decreases down the group. The key is the ease of losing or gaining electrons.
在第1族和第2族中，从上到下反应活泼性增强。在第6族和第7族中，从上到下反应活泼性减弱。关键在于失去或获得电子的难易程度。
For metals: the larger the atom, the weaker the attraction between the outer electron and the nucleus, so easier to lose an electron.
对金属而言：原子越大，外层电子与原子核之间的引力越弱，因此更容易失去电子。
For non-metals: the larger the atom, the greater the shielding effect, so the nucleus attracts the incoming electron less strongly.
对非金属而言：原子越大，屏蔽效应越强，因此原子核吸引外来电子的能力越弱。
This trend explains why potassium is more reactive than lithium, and why chlorine is more reactive than iodine.
这个趋势解释了为什么钾比锂活泼，以及为什么氯比碘活泼。
These patterns are consistent, so you can predict relative reactivity using atomic size and electron distance.
这些规律具有一致性，因此你可以通过原子大小和电子距离来预测相对活泼性。
11. Structure and Bonding Summary | 结构与成键总结
Atoms bond to achieve a full outer shell. Ionic bonding involves electron transfer, while covalent bonding involves electron sharing. The type of bond formed depends on the elements involved.
原子成键是为了达到最外层充满的状态。离子键涉及电子转移，共价键涉及电子共享。形成的键的类型取决于所涉及的元素。
Metal + non-metal → ionic compound.
金属 + 非金属 → 离子化合物。
Non-metal + non-metal → covalent compound.
非金属 + 非金属 → 共价化合物。
Ionic compounds have high melting points and conduct electricity when molten or dissolved.
离子化合物熔点高，在熔融或溶解状态下导电。
Simple covalent molecules have low melting points and do not conduct electricity.
简单共价分子熔点低，不能导电。
Make sure you can draw electron diagrams for ionic and covalent substances, such as sodium chloride and water.
务必确保你能画出离子和共价物质的电子示意图，例如氯化钠和水。
12. Final Exam Tips | 考试终极提示
In the exam, you will be asked to describe atomic structure, write electronic configurations, and explain trends in the Periodic Table. Practice reading nuclear notation and interpreting group/period information.
考试中，你会被要求描述原子结构、写出电子排布、解释周期表趋势。练习阅读核素符号并解读族和周期的信息。
Always state the number of protons, neutrons and electrons when asked about an atom.
当被问及原子时，务必给出质子、中子和电子的数目。
Use the correct terminology: 'atomic number' and 'mass number' are different from 'relative atomic mass'.
使用正确的术语：“原子序数”和“质量数”不同于“相对原子质量”。
For electron configurations, fill shells in the order 2, 8, 8 for the first 20 elements.
对于电子排布，前20号元素按2、8、8的顺序填充壳层。
When comparing reactivity, link your explanation to the distance of outer electrons and the attraction to the nucleus.
比较活泼性时，将解释联系到外层电子与原子核的距离以及吸引力。
Understanding atomic structure is the key to mastering the whole of chemistry. Use this guide to revise, then test yourself with past paper questions.
理解原子结构是掌握整个化学的关键。使用本指南复习，然后用历年真题测试自己。
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