📚 Atomic Structure and the Periodic Table | 原子结构与元素周期表
Welcome to this revision guide on atomic structure and the periodic table, designed for Edexcel IGCSE Science. This topic is central to your understanding of chemistry, and mastering it will help you explain the behaviour of all materials.
欢迎阅读这份针对 Edexcel IGCSE 科学考试的复习指南，主题是原子结构与元素周期表。该主题是理解化学的核心，掌握它能够帮助你解释所有物质的行为。
1. Atoms, Elements and Compounds | 原子、元素和化合物
An atom is the smallest particle of an element that can exist on its own. An element is a substance made of only one type of atom, while a compound is formed when two or more elements chemically combine in fixed proportions.
原子是元素能够独立存在的最小粒子。元素是由同一种原子组成的物质；而化合物则是由两种或多种元素按固定比例经化学结合形成的。
For example, sodium chloride (NaCl) is a compound containing sodium and chlorine atoms held together by ionic bonds.
例如，氯化钠（NaCl）是一种由钠原子和氯原子通过离子键结合而成的化合物。
Mixtures, unlike compounds, contain two or more substances that are not chemically joined. They can be separated by physical methods such as filtration or evaporation.
与化合物不同，混合物含有两种或多种未发生化学结合的物质，可以通过过滤或蒸发等物理方法进行分离。
2. Inside the Atom: Subatomic Particles | 原子内部：亚原子粒子
Every atom is composed of three main subatomic particles: protons, neutrons and electrons. The protons and neutrons are located in the central nucleus, while electrons orbit the nucleus in energy levels (shells).
每个原子都由三种主要的亚原子粒子组成：质子、中子和电子。质子和中子位于原子中心原子核内，而电子在核外的能级（电子层）中运动。
| Particle | Relative charge | Relative mass |
|---|---|---|
| Proton | +1 | 1 |
| Neutron | 0 | 1 |
| Electron | -1 | 1/1836 |
The positive charge of the protons is balanced by the negative charge of the electrons, so a neutral atom has an equal number of protons and electrons.
质子的正电荷与电子的负电荷相互抵消，因此中性原子的质子数与电子数相等。
3. Atomic Number and Mass Number | 原子序数与质量数
The atomic number (Z) is the number of protons in the nucleus of an atom. This 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）是原子核中质子数与中子数之和。
Atomic number (Z) = Number of protons = Number of electrons (in a neutral atom)
原子序数（Z）= 质子数 = 电子数（中性原子）
Mass number (A) = Number of protons + Number of neutrons
质量数（A）= 质子数 + 中子数
To find the number of neutrons in an atom, subtract the atomic number from the mass number: neutrons = A – Z.
要计算原子中的中子数，只需用质量数减去原子序数：中子数 = A – Z。
For example, an oxygen atom has Z = 8 and A = 16, so it contains 8 protons, 8 electrons and 8 neutrons.
例如，氧原子有 Z = 8、A = 16，因此它含有 8 个质子、8 个电子和 8 个中子。
4. Isotopes | 同位素
Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. This means they have the same atomic number but different mass numbers.
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，因此它们的原子序数相同而质量数不同。
For example, carbon-12 (C-12) has 6 protons and 6 neutrons, while carbon-14 (C-14) has 6 protons and 8 neutrons.
例如，碳-12（C-12）有 6 个质子和 6 个中子，而碳-14（C-14）有 6 个质子和 8 个中子。
Isotopes of an element have identical chemical properties because they have the same number of electrons. However, their physical properties, such as mass and density, may differ.
由于同位素具有相同的电子数，所以它们的化学性质完全相同。但它们的物理性质（如质量和密度）可能不同。
The relative atomic mass of an element is the weighted average mass of the isotopes in a naturally occurring sample, taking account of their relative abundances.
元素的相对原子质量是自然界样品中所有同位素质量的加权平均值，其中考虑了各同位素的相对丰度。
5. Electronic Configuration | 电子排布
Electrons occupy energy levels (shells) around the nucleus. The first shell can hold a maximum of 2 electrons, and the second and third shells can each hold up to 8 electrons.
电子占据原子核外的能层（电子层）。第一层最多容纳 2 个电子，第二、三层各最多容纳 8 个电子。
Electrons fill shells in order of increasing energy, from the innermost shell to the outermost shell.
电子按照从内层到外层、能量由低到高的顺序填入各电子层。
For example, the electronic configuration of sodium (Z = 11) is 2, 8, 1. This can be written as 2·8·1 or shown as a diagram.
例如，钠（Z = 11）的电子排布是 2, 8, 1，可写成 2·8·1 或用示意图表示。
The number of electrons in the outermost shell is called the valence electrons. These determine how the element reacts chemically.
最外层电子数称为价电子数，它决定了元素的化学性质。
6. The Periodic Table: Groups and Periods | 元素周期表：族和周期
The periodic table arranges all known elements in order of increasing atomic number. Elements in the same vertical column are called a group, and elements in the same horizontal row are called a period.
元素周期表按原子序数递增的顺序排列所有已知元素。同一竖列的元素称为族，同一横行的元素称为周期。
There are 18 groups and 7 periods in the modern periodic table. Elements in the same group have the same number of electrons in their outer shell, so they have similar chemical properties.
现代元素周期表共有 18 个族和 7 个周期。同一族元素的最外层电子数相同，因此化学性质相似。
Group number indicates the number of outer-shell electrons for the main groups. For example, Group 1 elements all have one outer electron.
族号表示主族元素的最外层电子数。例如，第 1 族元素都有一个外层电子。
The period number shows the number of occupied electron shells. A sodium atom (period 3) has three occupied shells.
周期数表示该元素原子有若干电子层被占据。钠原子位于第三周期，因此它有三个电子层。
7. Group 1 Alkali Metals | 第 1 族碱金属
Group 1 elements (lithium, sodium, potassium, rubidium, caesium, francium) are called alkali metals. They are soft, have low densities and react vigorously with water to produce hydrogen gas and an alkaline solution.
第 1 族元素（锂、钠、钾、铷、铯、钫）被称为碱金属。它们质软、密度小，与水剧烈反应生成氢气和碱性溶液。
Reactivity increases as you go down Group 1 because the outer electron is farther from the nucleus and is more easily lost. This is due to increased electron shielding.
随着族向下移动，碱金属的反应性增强，因为外层电子离原子核更远，更容易失去，这归因于电子屏蔽效应增强。
For example, lithium reacts slowly with water, sodium reacts quickly, and potassium reacts violently with a lilac flame.
例如，锂与水反应缓慢，钠与水反应较快，而钾与水反应剧烈并产生淡紫色火焰。
Alkali metals form ionic compounds with non-metals by losing their single outer electron, producing a 1+ ion.
碱金属与非金属形成离子化合物时失去单个外层电子，生成 +1 价离子。
8. Group 7 Halogens | 第 7 族卤素
Group 7 elements (fluorine, chlorine, bromine, iodine, astatine) are called halogens. They are non-metals that exist as diatomic molecules. Their reactivity decreases as you go down the group.
第 7 族元素（氟、氯、溴、碘、砹）被称为卤素。它们是非金属，以双原子分子形式存在。随着族向下移动，反应的活泼性减弱。
Halogens gain one electron to obtain a stable electronic configuration, forming a 1- ion. For example, chlorine gains one electron to become Cl⁻.
卤素得到一个电子以形成稳定的电子排布，生成 -1 价离子。例如，氯得到一个电子变为 Cl⁻。
A more reactive halogen can displace a less reactive halogen from a solution of its salt. For example, chlorine displaces iodine from potassium iodide solution.
活泼性较强的卤素可以将活泼性较弱的卤素从其盐溶液中置换出来。例如，氯能将碘从碘化钾溶液中置换出来。
The melting and boiling points of halogens increase as you go down the group, due to stronger van der Waals forces between larger molecules.
卤素的熔点和沸点随族向下移动而升高，这是由于较大分子间的范德华力更强。
9. Group 0 Noble Gases | 第 0 族稀有气体
Group 0 elements (helium, neon, argon, krypton, xenon, radon) are called noble gases. They are colourless, tasteless and very unreactive because their outer shells are full.
第 0 族元素（氦、氖、氩、氪、氙、氡）被称为稀有气体。它们无色无味，由于最外层电子已满而极不活泼。
Helium has 2 outer electrons, while neon and argon each have 8 outer electrons. This full outer shell gives them a stable electronic configuration.
氦有 2 个外层电子，而氖和氩各有 8 个外层电子。这种充满的最外层电子结构使它们具有稳定电子排布。
Noble gases are used in lighting, welding and providing inert atmospheres. For example, argon is used in filament light bulbs to prevent the tungsten wire from reacting with oxygen.
稀有气体可用于照明、焊接和提供惰性气氛。例如，氩气用于白炽灯泡中，防止钨丝与氧气反应。
10. Using the Periodic Table | 使用元素周期表
The periodic table allows you to predict the properties of an element based on its position. Elements on the left are metals, while elements on the right (except hydrogen) are non-metals.
元素周期表可以帮助你根据元素的位置预测其性质。左侧的元素是金属，右侧（除氢外）的元素是非金属。
Metals tend to lose electrons and form positive ions, whereas non-metals tend to gain electrons and form negative ions.
金属倾向于失去电子形成阳离子，而非金属倾向于得到电子形成阴离子。
Elements between metals and non-metals are called metalloids, such as silicon and germanium. They have intermediate properties.
位于金属与非金属之间的元素称为类金属，如硅和锗，它们的性质介于两者之间。
By knowing the group number and period number, you can quickly write the electronic configuration of a main-group element and deduce its likely charge when it reacts.
通过了解族号和周期号，你可以快速写出主族元素的电子排布，并推断它反应时的常见电荷。
11. Summary | 总结
Atomic structure and the periodic table are fundamental to IGCSE Science. Remember the three subatomic particles, how to calculate protons, neutrons and electrons, and how the position of an element helps predict its reactivity.
原子结构与元素周期表是 IGCSE 科学的基础。请牢记三种亚原子粒子、如何计算质子、中子和电子数，以及元素在周期表中的位置如何帮助预测其反应性。
Key terms: atom, element, compound, isotope, atomic number, mass number, electronic configuration, group, period, valence electrons.
关键术语：原子、元素、化合物、同位素、原子序数、质量数、电子排布、族、周期、价电子。
Practise drawing electronic configurations and comparing Group 1 and Group 7 trends to secure full marks in your exams.
练习绘制电子排布图，并比较第 1 族和第 7 族性质的递变规律，这样可以在考试中拿全分。
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