Atomic Structure and the Periodic Table | 原子结构与元素周期表

📚 Atomic Structure and the Periodic Table | 原子结构与元素周期表

Understanding atomic structure is essential for every IGCSE Science student. The Periodic Table is not just a list of elements; it is a powerful tool that organises the physical and chemical properties of matter. This article covers the key ideas you need for your Edexcel IGCSE Science examinations.

理解原子结构是每一位 IGCSE 科学学生的基础。元素周期表不仅仅是一张元素列表，更是一个整理物质物理和化学性质的强大工具。本文涵盖了你在 Edexcel IGCSE 科学考试中需要掌握的核心要点。

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1. Atoms: Building Blocks of Matter | 原子：物质的基本组成

Atoms are the smallest neutral particles of an element. Each atom has a central nucleus containing protons and neutrons, surrounded by electrons moving in shells or energy levels.

原子是元素中呈电中性的最小粒子。每个原子都有一个包含质子和中子的原子核，周围是电子，它们在壳层或能级中运动。

Particle	Relative charge	Relative mass
Proton	+1	1
Neutron	0	1
Electron	-1	1/1836

The nucleus is tiny and dense, while the electrons occupy most of the atomic volume. The number of electrons always equals the number of protons in a neutral atom.

原子核微小而致密，电子则占据了原子的大部分体积。在电中性原子中，电子数总是等于质子数。

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2. Atomic Number and Mass Number | 原子序数与质量数

The atomic number (proton number) Z is the number of protons in the nucleus. The mass number A is the total number of protons and neutrons in the nucleus.

原子序数（质子数）Z 是原子核中的质子数目。质量数 A 是原子核中质子与中子的总数目。

Mass number (A) = number of protons + number of neutrons

质量数 A = 质子数 + 中子数

For a neutral atom, the atomic number also tells us the number of electrons. For example, a sodium atom has Z = 11 and A = 23, so it contains 11 protons, 11 electrons and 12 neutrons.

对于中性原子，原子序数还告诉我们电子数。例如，一个钠原子 Z = 11，A = 23，因此它含有 11 个质子、11 个电子和 12 个中子。

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3. 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的原子，它们具有相同的质子数和不同的中子数。这意味着它们具有相同的原子序数，但质量数不同。

• Carbon-12 has 6 protons and 6 neutrons; carbon-14 has 6 protons and 8 neutrons.

  碳-12 有 6 个质子和 6 个中子；碳-14 有 6 个质子和 8 个中子。

• Chlorine-35 and chlorine-37 are isotopes of chlorine, with 17 protons and 18 or 20 neutrons respectively.

  氯-35 和氯-37 是氯的同位素，分别含有 17 个质子，以及 18 或 20 个中子。

Isotopes of the same element have identical chemical properties because chemical behaviour depends on the number of electrons. However, they may have different physical properties such as mass or density.

同一元素的同位素具有完全相同的化学性质，因为化学行为取决于电子数目。但是，它们的物理性质（如质量或密度）可能不同。

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4. Electronic Configuration | 电子排布

Electrons occupy shells in order of increasing energy. The first shell can hold up to 2 electrons, and the second and third shells can each hold up to 8 electrons.

电子按能量升高的顺序填充壳层。第一壳层最多容纳 2 个电子，第二和第三壳层各自最多容纳 8 个电子。

Shell 1: 2 → Shell 2: 8 → Shell 3: 8

第一壳层：2 → 第二壳层：8 → 第三壳层：8

For example, sodium has 11 electrons, so its electronic configuration is 2,8,1. Chlorine has 17 electrons, so its configuration is 2,8,7.

例如，钠有 11 个电子，所以其电子排布为 2,8,1。氯有 17 个电子，因此其电子排布为 2,8,7。

The electronic configuration determines how an element reacts and which ion it forms.

电子排布决定了元素如何发生反应以及它会形成何种离子。

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5. The Periodic Table | 元素周期表

The Periodic Table arranges all known elements in order of increasing atomic number. The rows are called periods and the columns are called groups.

元素周期表按照原子序数递增的顺序排列所有已知元素。横行称为周期，纵列称为族。

An element within the Periodic Table can be located using its electronic configuration. For a main group element, the number of outer electrons equals the group number, and the number of occupied shells equals the period number.

元素在周期表中的位置可以根据其电子排布来确定。对于主族元素，最外层电子数等于族序数，而电子壳层数等于周期数。

Element	Electronic configuration	Period	Group
Sodium	2,8,1	3	1
Chlorine	2,8,7	3	7

The periodic table helps scientists predict trends in reactivity, melting points and the types of compounds formed.

周期表帮助科学家预测反应活性、熔点和所形成化合物类型的趋势。

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6. Group 1: Alkali Metals | 第1族：碱金属

Group 1 elements are soft, shiny metals with low densities. They have one outer electron, which they lose easily to form +1 ions.

第1族元素是柔软、有光泽且密度较低的金属。它们只有一个最外层电子，容易失去而形成 +1 离子。

• All Group 1 metals react vigorously with water to produce hydrogen gas and an alkaline solution.

  所有第1族金属都会与水剧烈反应，生成氢气和碱性溶液。

• Reactivity increases down the group as the outer electron becomes more easily lost.

  随着原子半径增大，最外层电子更容易失去，因此反应活性自上而下增强。

2Li + 2H₂O → 2LiOH + H₂

2Li + 2H₂O → 2LiOH + H₂↑

Melting points and boiling points decrease down the group.

第1族元素的熔点和沸点随原子序数增加而降低。

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7. Group 7: Halogens | 第7族：卤素

Group 7 elements are non-metals with seven outer electrons. They gain one electron to form -1 ions and exist as diatomic molecules, such as F₂, Cl₂, Br₂ and I₂.

第7族元素是具有七个最外层电子的非金属。它们获得一个电子形成 -1 离子，并且以双原子分子存在，如 F₂、Cl₂、Br₂ 和 I₂。

Halogens have colored vapours and their melting and boiling points increase down the group. In contrast to Group 1, reactivity decreases down the group because it is harder for the atom to attract an extra electron.

卤素具有有色蒸气，其熔点和沸点随原子序数增加而升高。与第1族相反，卤素反应活性自上而下减弱，因为原子吸引额外电子变得更困难。

A more reactive halogen can displace a less reactive halogen from a solution of its salt.

活动性较强的卤素可以将其盐溶液中的活动性较弱的卤素置换出来。

Cl₂ + 2KI → 2KCl + I₂

Cl₂ + 2KI → 2KCl + I₂

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8. Group 0: Noble Gases | 第0族：稀有气体

Group 0 elements are the noble gases. They have full outer electron shells, which makes them very unreactive.

第0族元素是稀有气体。它们具有全满的最外层电子壳层，因此非常不活泼。

• Helium, neon and argon are monatomic gases.

  氦、氖和氩都是单原子气体。

• They have low boiling points and do not easily form compounds.

  它们的沸点很低，并且不容易形成化合物。

Noble gases are used in lighting and as inert atmospheres for welding because they are chemically stable.

稀有气体因化学稳定性高，被用于照明灯具并可作为焊接时的惰性保护气体。

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9. Metals and Non-Metals | 金属与非金属

Metals are found on the left and in the middle of the Periodic Table. Non-metals are found on the right side. The metallic character decreases along a period from left to right.

金属位于元素周期表的左侧和中部，非金属位于右侧。在同一周期内，金属性从左到右逐渐减弱。

Metals	Non-metals
Shiny and conductive | 有光泽、能导电	Dull and mostly poor conductors | 无光泽、大多不导电
Malleable and ductile | 可延展、可拉丝	Brittle when solid | 固态时脆
Form basic oxides | 形成碱性氧化物	Form acidic oxides | 形成酸性氧化物

Some elements, such as silicon and germanium, show properties between metals and non-metals and are called metalloids.

一些元素如硅和锗表现出介于金属和非金属之间的性质，被称为类金属。

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10. Predicting Properties from the Periodic Table | 利用周期表预测性质

Once you know an element’s group and period, you can predict many of its properties without memorising them.

一旦你知道某个元素所在的主族和周期，就可以预测它的许多性质，而不需要死记硬背。

For example, caesium is in Group 1 below sodium. You can predict that caesium is a very soft metal with low density, loses one electron to form Cs⁺, and reacts explosively with water.

例如，铯位于钠下方的第1族。你可以预测铯是一种非常柔软的金属，密度较低，容易失去一个电子形成 Cs⁺，并且会与水发生爆炸性反应。

Similarly, astatine is below iodine in Group 7. It is likely to be a dark, brittle non-metal with a high boiling point, and it will be less reactive than iodine.

类似地，砹位于碘下方的第7族。它可能是一种深色、易碎的非金属，沸点较高，并且反应活性低于碘。

The Periodic Table therefore becomes a logical framework that helps you connect structure, position and reactivity.

因此，元素周期表成为一个有逻辑的框架，帮助你连接结构、位置和反应活性。

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