📚 Atomic Structure and the Periodic Table | 原子结构与元素周期表
This article reviews the key concepts of atomic structure and the periodic table for the Edexcel IGCSE Science course. We will look at the particles inside the atom, how electrons are arranged, and why the periodic table is arranged the way it is.
本文复习 Edexcel IGCSE 科学课程中关于原子结构和元素周期表的核心概念。我们将探讨原子内部的粒子、电子的排布方式，以及元素周期表为什么这样排列。
1. The Atom | 原子
An atom is the smallest part of an element that can exist. Every element is made of its own unique atoms. Atoms are extremely small – about one ten-millionth of a millimetre across.
原子是元素能够存在的最小微粒。每种元素都由其特有的原子组成。原子极小——直径大约只有一毫米的千万分之一。
An atom contains a central nucleus and electrons that move around the outside. Most of the atom is actually empty space.
原子含有一个位于中心的原子核，以及围绕核外运动的电子。实际上，原子的大部分区域是空的空间。
2. Subatomic Particles | 亚原子粒子
There are three subatomic particles you need to know: protons, neutrons and electrons. They are located in different parts of the atom and carry different charges and masses.
你需要掌握三种亚原子粒子：质子、中子和电子。它们位于原子的不同部分，带有不同的电荷和质量。
| Particle | Charge | Mass | Location |
| Proton | +1 | 1 | Nucleus |
| Neutron | 0 | 1 | Nucleus |
| Electron | -1 | 1/1836 | Outside nucleus |
Charge of a proton = +1, electron = -1, neutron = 0
质子的电荷 = +1，电子 = -1，中子 = 0
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. It identifies the element. 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。它决定了元素的种类。质量数（A）是原子核中质子数和中子数的总和。
You can calculate the number of neutrons using the formula:
Number of neutrons = mass number - atomic number
中子数 = 质量数 - 原子序数
For example, sodium has an atomic number of 11 and a mass number of 23. Therefore it has 11 protons, 11 electrons and 12 neutrons.
例如，钠的原子序数为11，质量数为23。因此它有11个质子、11个电子和12个中子。
4. Isotopes | 同位素
Isotopes are atoms of the same element with the same number of protons but different numbers of neutrons. This means they have the same atomic number but different mass numbers.
同位素是同一元素的原子，它们具有相同的质子数但不同的中子数。这意味着它们的原子序数相同，但质量数不同。
For instance, carbon-12 and carbon-14 are isotopes of carbon. Both have 6 protons, but carbon-12 has 6 neutrons and carbon-14 has 8 neutrons.
例如，碳-12和碳-14是碳的同位素。两者都有6个质子，但碳-12有6个中子，而碳-14有8个中子。
Isotopes have the same chemical properties because they have the same number of electrons. However, their physical properties may differ, such as mass and density.
同位素具有相同的化学性质，因为它们具有相同数量的电子。然而，它们的物理性质可能不同，例如质量和密度。
5. Electronic Configuration | 电子排布
Electrons are arranged in shells (energy levels) around the nucleus. Each shell can hold a limited number of electrons. The first shell holds up to 2 electrons, the second shell holds up to 8 electrons, and the third shell holds up to 8 electrons.
电子在原子核周围的壳层（能级）中排列。每个壳层能容纳有限数量的电子。第一壳层最多容纳2个电子，第二壳层最多容纳8个电子，第三壳层最多容纳8个电子。
You can write the electronic configuration as numbers, for example, sodium (11 electrons) has the configuration 2.8.1.
可以用数字写出电子排布，例如，钠（11个电子）的排布是2.8.1。
Electronic configuration of sodium: 2, 8, 1
钠的电子排布：2, 8, 1
The electrons in the outermost shell are called valence electrons. They are responsible for the element's chemical reactivity.
最外层壳层中的电子称为价电子。它们决定了该元素的化学反应活性。
6. The Periodic Table | 元素周期表
The periodic table arranges elements in order of increasing atomic number. Elements with similar properties are placed in the same vertical column, called a group.
元素周期表按原子序数递增的顺序排列元素。具有相似性质的元素位于同一纵列中，称为族。
There are 18 groups in the full periodic table. For the IGCSE course, you mainly need to know about Groups 1, 2, 7 and 0.
完整周期表有18个族。对于IGCSE课程，你主要需要了解第1、2、7和0族。
Rows in the periodic table are called periods. The period number tells you how many shells the atoms have. For example, elements in Period 3 have three shells.
周期表中的横行称为周期。周期数告诉你原子的电子壳层数。例如，第3周期的元素有3个壳层。
7. Group 1: The Alkali Metals | 第1族：碱金属
Group 1 elements are called the alkali metals. They include lithium, sodium, potassium, rubidium and caesium. They are soft, shiny metals with low densities.
第1族元素称为碱金属。它们包括锂、钠、钾、铷和铯。它们是柔软、有光泽且密度较低的金属。
Alkali metals have one electron in their outer shell. They lose this electron when reacting, forming a 1+ ion.
碱金属最外层有一个电子。在反应时它们会失去这个电子，形成带1+电荷的离子。
They are very reactive and react vigorously with water to produce hydrogen gas and an alkaline solution. For example:
它们非常活泼，与水反应剧烈，产生氢气和碱性溶液。例如：
2Na + 2H₂O → 2NaOH + H₂
2Na + 2H₂O → 2NaOH + H₂
Reactivity increases down the group as the outer electron is further from the nucleus and is easier to lose.
同族中从上到下活泼性增强，因为最外层电子离原子核更远，更容易失去。
8. Group 7: The Halogens | 第7族：卤素
Group 7 elements are called the halogens. They include fluorine, chlorine, bromine and iodine. They are non-metals with characteristic colours at room temperature.
第7族元素称为卤素。它们包括氟、氯、溴和碘。它们是非金属，在室温下具有特征颜色。
Halogens have seven electrons in their outer shell. They gain one electron when reacting, forming a 1- ion.
卤素最外层有7个电子。在反应时它们会获得一个电子，形成带1-电荷的离子。
Reactivity decreases down the group. A more reactive halogen can displace a less reactive halogen from a solution of its salt. For example:
同族中从上到下活泼性减弱。较活泼的卤素可以将较不活泼的卤素从其盐溶液中置换出来。例如：
Cl₂ + 2NaBr → 2NaCl + Br₂
Cl₂ + 2NaBr → 2NaCl + Br₂
9. Group 0: The Noble Gases | 第0族：稀有气体
Group 0 elements are called the noble gases. They include helium, neon, argon, krypton and xenon. They are colourless gases with very low reactivity.
第0族元素称为稀有气体。它们包括氦、氖、氩、氪和氙。它们是无色、反应活性极低的气体。
Noble gases have a full outer shell of electrons (2 for helium, 8 for the others). This makes them stable and unreactive. They exist as single atoms.
稀有气体具有满电子最外层（氦为2个，其他为8个）。这使得它们稳定且不易反应。它们以单原子形式存在。
Helium is used in balloons, argon is used in light bulbs, and neon is used in signs.
氦用于气球，氩用于灯泡，氖用于霓虹灯。
10. Metals and Non-Metals | 金属与非金属
The periodic table is divided into metals and non-metals by a zigzag line. Metals are on the left and centre, non-metals are on the right.
元素周期表由一条折线分为金属和非金属。金属在左侧和中间，非金属在右侧。
Metals are shiny, malleable, good conductors of heat and electricity, and usually have high melting points. Non-metals are dull, brittle, poor conductors, and have lower melting points.
金属有光泽、可锻、是热和电的良导体，通常熔点较高。非金属无光泽、易碎、导电性差，熔点较低。
Elements in the same group often have similar chemical and physical properties because they have the same number of outer electrons.
同一族的元素通常具有相似的化学和物理性质，因为它们具有相同数量的最外层电子。
11. Ions and Ionic Bonding | 离子与离子键
Atoms can lose or gain electrons to become stable. When an atom loses or gains electrons, it becomes a charged particle called an ion.
原子可以通过失去或获得电子来达到稳定。当原子失去或获得电子时，它变成带电粒子，称为离子。
Metals lose electrons to form positive ions (cations). Non-metals gain electrons to form negative ions (anions).
金属失去电子形成正离子（阳离子）。非金属获得电子形成负离子（阴离子）。
Oppositely charged ions are held together by strong electrostatic forces. This is called ionic bonding. For example, sodium chloride (Na⁺Cl⁻) forms an ionic lattice.
带相反电荷的离子通过强烈的静电作用力结合在一起。这称为离子键。例如，氯化钠（Na⁺Cl⁻）形成离子晶格。
Na + Cl → Na⁺ + Cl⁻
Na + Cl → Na⁺ + Cl⁻
12. Covalent Bonding | 共价键
Covalent bonding occurs when non-metal atoms share pairs of electrons. Each shared pair forms a covalent bond.
共价键发生在非金属原子之间共享电子对时。每一对共享电子形成一个共价键。
For example, a hydrogen molecule (H₂) has two hydrogen atoms sharing one pair of electrons. A water molecule (H₂O) has two hydrogen atoms covalently bonded to one oxygen atom.
例如，氢分子（H₂）中两个氢原子共享一对电子。水分子（H₂O）中两个氢原子与一个氧原子通过共价键结合。
Simple covalent substances have low melting and boiling points because the intermolecular forces are weak. They do not conduct electricity.
简单的共价物质具有较低的熔点和沸点，因为分子间作用力较弱。它们不导电。
H· + ·H → H:H (shared electron pair)
H· + ·H → H:H（共享电子对）
Conclusion | 总结
Understanding atomic structure and the periodic table is the foundation of chemistry. Knowing how protons, neutrons and electrons are arranged helps predict an element's properties and how it will react.
理解原子结构和元素周期表是化学的基础。了解质子、中子和电子的排列有助于预测元素的性质以及它如何反应。
Remember the key patterns across the periodic table: groups show similar outer-electron configurations, periods show the number of shells, and the group number often links to the number of outer electrons.
记住周期表中的关键规律：族表示相似的最外层电子排布，周期表示壳层数，而族号通常与最外层电子数相关。
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