📚 Atomic Structure and the Periodic Table | 原子结构与元素周期表
This article covers the core concepts of atomic structure and the periodic table as required for the Edexcel IGCSE Science specification. It is designed to help you understand the building blocks of matter and the logic behind the arrangement of elements.
本文涵盖 Edexcel IGCSE 科学大纲中关于原子结构和元素周期表的核心概念，旨在帮助你理解物质的基本构成以及元素排列背后的逻辑。
1. The Development of the Atomic Model | 原子模型的发展
Scientists have refined the model of the atom over centuries. Dalton proposed that atoms were solid, indivisible spheres. Thomson discovered the electron and suggested the ‘plum pudding’ model, where negative electrons were embedded in a positive sphere.
科学家们经过数百年不断改进原子的模型。道尔顿提出原子是实心的、不可再分的球体。汤姆逊发现了电子，并提出了“葡萄干布丁”模型，认为带负电的电子镶嵌在带正电的球体中。
Rutherford’s gold foil experiment showed that the atom is mostly empty space with a tiny, dense, positively charged nucleus. This led to the nuclear model. Later, Bohr placed electrons in fixed orbits, and the current model describes electrons as existing in energy levels or shells.
卢瑟福的金箔实验表明，原子内部大部分是空的，中心有一个微小、致密且带正电的原子核，由此提出了核式模型。后来玻尔将电子置于固定的轨道上，而现代模型则描述电子存在于能量层或电子壳层中。
2. Subatomic Particles | 亚原子粒子
Atoms are made of three types of subatomic particles: protons, neutrons, and electrons. Their properties are summarised in the table below.
原子由三种亚原子粒子组成：质子、中子和电子。它们的性质总结如下表。
| Particle | Relative Charge | Relative Mass | Location |
|---|---|---|---|
| Proton | +1 | 1 | Nucleus |
| Neutron | 0 | 1 | Nucleus |
| Electron | -1 | 1/1840 | Shells |
Remember that the nucleus contains protons and neutrons, so it has a positive charge overall. Electrons move in shells around the nucleus.
请记住，原子核包含质子和中子，因此整体带正电。电子在原子核周围的壳层中运动。
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. It identifies the element and equals the number of electrons in a neutral atom. The mass number (A) is the total number of protons and neutrons.
原子序数（Z）是指原子核中的质子数，它决定了元素的种类，并且在电中性原子中等于电子数。质量数（A）是质子和中子数的总和。
Nucleons = Protons + Neutrons → Mass Number
核子数 = 质子数 + 中子数 → 质量数
For example, a sodium atom has atomic number 11 and mass number 23. It has 11 protons, 11 electrons, and 12 neutrons (23 – 11 = 12).
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（23 − 11 = 12）。
4. Isotopes | 同位素
Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. They therefore have the same atomic number but different mass numbers.
同位素是指同一元素中原子的质子数相同、但中子数不同的原子。因此它们具有相同的原子序数，但质量数不同。
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All isotopes of an element have identical chemical properties because they have the same electron arrangement.
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Their physical properties may differ, such as mass and density.
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同一元素的所有同位素具有相同的化学性质，因为它们的电子排布相同。
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它们的物理性质可能不同，例如质量密度。
Examples include carbon-12 and carbon-14, and chlorine-35 and chlorine-37. Radioactive isotopes are used in medicine and archaeology.
例如碳-12和碳-14，氯-35和氯-37。放射性同位素用于医学和考古学中。
5. Electronic Configurations | 电子排布
Electrons are arranged in shells (energy levels) around the nucleus. Each shell can hold a maximum number of electrons: the first shell holds 2, the second holds 8, and the third holds 8 (for the first ten elements).
电子围绕原子核分布在壳层（能级）上。每个壳层最多能容纳一定数量的电子：第一层为2个，第二层为8个，第三层为8个（对于前十个元素来说）。
2, 8, 8, … (maximum electrons per shell)
2，8，8……（每层最多电子数）
For example, oxygen (atomic number 8) has an electronic configuration of 2.6. Sodium (atomic number 11) has 2.8.1. The number of electrons in the outermost shell determines the chemical properties of the atom.
例如，氧（原子序数8）的电子排布为2.6。钠（原子序数11）为2.8.1。最外层电子数决定了原子的化学性质。
6. The Periodic Table Arrangement | 元素周期表的排列
The periodic table arranges elements in order of increasing atomic number. It is divided into rows called periods and columns called groups. Each element is represented by its symbol, atomic number, and relative atomic mass.
元素周期表按原子序数递增的顺序排列元素。它被分成称为“周期”的行和称为“族”的列。每种元素用符号、原子序数和相对原子质量表示。
Modern Periodic Law: properties of elements are a periodic function of their atomic number.
现代周期律：元素的性质是原子序数的周期函数。
Elements in the same group have the same number of electrons in their outer shell, giving them similar chemical properties. For example, Group 1 elements all have one outer electron.
同一族的元素具有相同的最外层电子数，因此化学性质相似。例如，第一族元素都只有一个最外层电子。
7. Periods and Groups | 周期与族
There are seven periods in the periodic table. As you move across a period, the atomic number increases, and the number of outer electrons increases from 1 to 8.
元素周期表中有七个周期。从左到右，原子序数递增，最外层电子数从1增加到8。
Groups are numbered from 1 to 8 (or 0 in some older conventions). Group number indicates the number of outer electrons for elements in that group, except for transition metals which are not in groups 1-8.
族编号从1到8（旧版也有用0的）。族号表示该族元素的最外层电子数，但过渡金属例外，它们不属于第1-8族。
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Group 1: alkali metals – highly reactive metals.
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Group 2: alkaline earth metals – reactive metals.
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Group 7: halogens – reactive non-metals.
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Group 8/0: noble gases – unreactive, full outer shell.
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第1族：碱金属——高活性金属。
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第2族：碱土金属——较活泼金属。
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第7族：卤素——活泼非金属。
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第8/0族：稀有气体——惰性，最外层满电子。
8. Trends Across a Period | 周期内元素的递变规律
Across a period from left to right, elements change from metallic to non-metallic. For example, sodium is a metal, silicon is a metalloid, and chlorine is a non-metal. This is due to increasing nuclear charge without adding extra shells.
在同周期中从左到右，元素从金属变为非金属。例如，钠是金属，硅是准金属，氯是非金属。这是因为核电荷增加而电子壳层数没有增加。
Atomic radius decreases across a period because the increased nuclear charge pulls the outer electrons closer to the nucleus. Ionisation energy generally increases across a period.
原子半径在同周期内减小，因为增加的核电荷将外层电子拉得更靠近原子核。电离能在一周期内通常增大。
9. Groups 1 and 7 Compared | 第1族与第7族的对比
Group 1 metals (alkali metals) are soft, have low densities, and react vigorously with water producing hydrogen and hydroxide. Their reactivity increases down the group because the outer electron becomes easier to lose as the atom gets larger.
第1族金属（碱金属）质软、密度小，能与水剧烈反应生成氢气和氢氧化物。它们的反应活性随原子序数增大而增强，因为原子变大，最外层电子更容易失去。
Group 7 elements (halogens) are non-metals with seven outer electrons. They tend to gain one electron to form negative ions. Their reactivity decreases down the group because the atoms get bigger and the attraction for an extra electron becomes weaker.
第7族元素（卤素）是非金属，有7个最外层电子。它们倾向于获得一个电子形成负离子。它们的反应活性随原子序数增大而减弱，因为原子变大，对额外电子的吸引力变弱。
10. Metals, Non-metals, and Metalloids | 金属、非金属和准金属
Metals are found on the left and middle of the periodic table. They are shiny, good conductors of heat and electricity, malleable, ductile, and lose electrons to form positive ions.
金属位于周期表的左侧和中间。它们有光泽，是良好的电和热导体，具有延展性和可锻性，且易失去电子形成正离子。
Non-metals are found on the upper right of the table. They are dull, poor conductors, brittle when solid, and gain electrons to form negative ions. Some elements, like boron and silicon, have intermediate properties and are called metalloids.
非金属位于周期表的右上角。它们表面暗淡，是不良导体，固体时易碎，且易获得电子形成负离子。一些元素如硼和硅具有中间性质，被称为准金属。
Understanding the position of an element in the periodic table allows you to predict its physical and chemical properties. This is central to the Edexcel IGCSE Science course.
理解元素在周期表中的位置，能帮助你预测其物理和化学性质。这是 Edexcel IGCSE 科学课程的核心内容。
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