📚 Structure of the Atom and the Periodic Table | 原子结构与元素周期表
Understanding the structure of the atom and how the periodic table is organised is a fundamental part of IGCSE Science. This knowledge explains why elements react in certain ways, how ions form, and why the periodic table is arranged as it is. In this article, we will break down the key concepts step by step, focusing on what you need to know for the Edexcel IGCSE Science examinations.
理解原子结构以及元素周期表的组织方式是 IGCSE 科学的重要组成部分。这些知识解释了元素为何以特定方式发生反应、离子如何形成，以及元素周期表为何如此排列。在本文中，我们将循序渐进地分解关键概念，聚焦 Edexcel IGCSE 科学考试中你需要掌握的内容。
1. The Atomic Model | 原子模型
Atoms are the smallest particles of an element that retain the chemical properties of that element. The modern model of the atom describes a central nucleus surrounded by electrons that occupy energy levels (shells). The nucleus is very small and dense, containing protons and neutrons.
原子是保持元素化学性质的最微小粒子。现代原子模型描述了一个位于中央的原子核，周围环绕着占据能级（电子壳层）的电子。原子核非常小且致密，包含质子和中子。
Key points to remember:
- Atoms are electrically neutral because the number of protons equals the number of electrons.
- Electrons move around the nucleus in fixed energy levels, not in random paths.
- The nucleus contains almost all the mass of the atom.
- 原子呈电中性，因为质子数等于电子数。
- 电子在固定能级上绕核运动，而不是随机路径。
- 原子核几乎包含了原子的全部质量。
This model has evolved over time: from Dalton’s solid sphere, to Thomson’s ‘plum pudding’, then Rutherford’s nuclear model, and finally Bohr’s planetary model with shells. For IGCSE, you need to be comfortable with the main features of the modern model and how evidence led to its development.
这一模型随着时间不断演变：从道尔顿的实心球体，到汤姆森的“葡萄干布丁”模型，再到卢瑟福的有核模型，最后是玻尔的壳层行星模型。对于 IGCSE，你需要熟悉现代模型的主要特征，以及证据如何推动了它的发展。
2. Subatomic Particles | 亚原子粒子
There are three subatomic particles that make up an atom. Their properties are summarised in the table below.
构成原子的亚原子粒子有三种。它们的性质总结在下表中。
| Particle | Charge | Mass (relative) | Location |
| Proton 质子 |
+1 | 1 | Nucleus 原子核 |
| Neutron 中子 |
0 | 1 | Nucleus 原子核 |
| Electron 电子 |
-1 | 1/1836 (negligible) | Shells 电子壳层 |
Protons have a relative charge of +1 and a relative mass of 1. Neutrons are neutral and also have a relative mass of 1. Electrons have a relative charge of -1 and a mass so small it is often taken as zero.
质子带 +1 相对电荷，相对质量为 1。中子不带电，相对质量也为 1。电子带 -1 相对电荷，质量非常小，通常可忽略不计。
3. 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. The mass number (A) is the total number of protons plus neutrons. The notation for an element X is written as shown:
原子序数（Z）是原子核中的质子数。质量数（A）是质子数 + 中子数的总和。元素 X 的表示方式如下：
ᴬ_Z X (for example, ³⁵₁₇Cl)
For a neutral atom, the number of electrons equals the number of protons. To find the number of neutrons, subtract the atomic number from the mass number:
对于中性原子，电子数等于质子数。要求中子数，用质量数减去原子序数：
Number of neutrons = Mass number − Atomic number
Example: For carbon-12 (¹²₆C), there are 6 protons, 6 neutrons and 6 electrons.
例如：对于碳-12（¹²₆C），有 6 个质子、6 个中子和 6 个电子。
4. Isotopes | 同位素
Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. Because they have the same number of protons, they have the same atomic number and the same chemical properties. However, their physical properties may differ slightly, such as density and melting point.
同位素是同一元素中质子数相同但中子数不同的原子。由于它们质子数相同，因此原子序数相同，化学性质也相同。但它们的物理性质可能略有不同，例如密度和熔点。
Common examples:
- Hydrogen-1 (¹₁H) and hydrogen-2 (deuterium, ²₁H)
- Carbon-12 (¹²₆C) and carbon-14 (¹⁴₆C)
- Chlorine-35 (³⁵₁₇Cl) and chlorine-37 (³⁷₁₇Cl)
- 氢-1（¹₁H）和氢-2（氘，²₁H）
- 碳-12（¹²₆C）和碳-14（¹⁴₆C）
- 氯-35（³⁵₁₇Cl）和氯-37（³⁷₁₇Cl）
Isotopes are used in medicine, dating ancient objects (carbon dating), and in nuclear power. For IGCSE, you should be able to calculate the relative atomic mass (Aᵣ) of an element from the abundance of its isotopes.
同位素用于医学、古老物体测年（碳测年）以及核能。对于 IGCSE，你需要能够根据同位素丰度计算元素的相对原子质量（Aᵣ）。
5. Electronic Configuration | 电子排布
Electrons are arranged in shells (energy levels) around the nucleus. Each shell can hold a certain maximum number of electrons: the first shell holds up to 2, the second shell up to 8, and the third shell up to 8 (for the first 20 elements).
电子围绕原子核排列在壳层（能级）中。每个壳层可容纳的最大电子数有限：第一层最多 2 个，第二层最多 8 个，第三层最多 8 个（对于前 20 号元素而言）。
To write the electronic configuration, fill the lowest energy shells first. For example:
要写出电子排布，需先填满能量最低的壳层。例如：
- Oxygen (8 electrons): 2, 6
- Sodium (11 electrons): 2, 8, 1
- Calcium (20 electrons): 2, 8, 8, 2
- 氧（8 个电子）：2, 6
- 钠（11 个电子）：2, 8, 1
- 钙（20 个电子）：2, 8, 8, 2
The number of electrons in the outermost shell determines how reactive an element is and how it bonds. Elements in the same group of the periodic table have the same number of outer-shell electrons, which is why they have similar chemical properties.
最外层电子数决定了元素的反应活性以及它的成键方式。元素周期表中同族元素具有相同的最外层电子数，因此它们具有相似的化学性质。
6. The Periodic Table | 元素周期表
The periodic table arranges elements in order of increasing atomic number. It is divided into rows (periods) and columns (groups). Elements in the same group have the same number of outer-shell electrons. The group number for main-group elements often tells you the number of outer electrons (for Groups 1, 2 and 3–8).
元素周期表按原子序数递增的顺序排列元素。它分为行（周期）和列（族）。同族元素具有相同的最外层电子数。对于主族元素，族号通常可以告诉你最外层电子数（对于第 1、2 族和第 3–8 族）。
The table shows trends in metallic character, and it is divided into metals (on the left) and non-metals (on the right). The periodic table is a powerful tool for predicting properties of elements.
周期表显示了金属性的变化趋势，并分为金属（左侧）和非金属（右侧）。周期表是预测元素性质的强大工具。
For Edexcel IGCSE Science, you should be able to identify the position of an element from its electronic configuration and vice versa. For example, an element with configuration 2,8,5 is in period 3 and group 5 (or group 15 using modern numbering).
对于 Edexcel IGCSE 科学，你需要能够根据电子排布确定元素的位置，反之亦然。例如，电子排布为 2,8,5 的元素位于第 3 周期第 5 族（或现代编号的第 15 族）。
7. Trends in the Periodic Table | 周期表规律
Moving down a group, the number of shells increases, so atoms get larger. The outermost electrons are further from the nucleus, so they are less tightly held. This affects reactivity.
在同一族中向下移动，电子壳层数量增加，因此原子变大。最外层电子离原子核更远，被束缚得较弱，这影响了反应活性。
Moving across a period, the number of protons increases, and the electrons are added to the same shell. The nuclear charge increases, attracting electrons more strongly, so atomic radius decreases across a period.
在同一周期中横向移动，质子数增加，电子被加到同一壳层。核电荷增加，对电子的吸引力更强，因此原子半径在同一周期中从左到右减小。
Metallic character decreases across a period and increases down a group. Non-metallic character increases across a period and decreases down a group.
金属性在周期中从左到右减弱，在族中从上到下增强。非金属性在周期中从左到右增强，在族中从上到下减弱。
8. Group 1 (Alkali Metals) | 第 1 族（碱金属）
Group 1 metals, such as lithium, sodium and potassium, have one electron in their outer shell. They are very reactive, and their reactivity increases down the group. They all form compounds with a charge of +1.
第 1 族金属，如锂、钠和钾，最外层有 1 个电子。它们非常活泼，且反应活性在同族中从上到下增强。它们形成 +1 价的化合物。
Typical properties:
- Soft, low density metals
- React vigorously with water to form hydrogen and a hydroxide
- Form white solids — oxides, chlorides, etc.
- 柔软、密度低的金属
- 与水剧烈反应生成氢气和氢氧化物
- 形成白色固体——氧化物、氯化物等
As you go down Group 1, the outer electron is further from the nucleus and is shielded by inner shells, so it is more easily lost. This explains why caesium reacts faster than lithium.
在向下移过第 1 族时，最外层电子离核更远，受到内层电子的屏蔽，因此更容易失去。这解释了为什么铯的反应速度比锂快。
9. Group 7 (Halogens) | 第 7 族（卤素）
Group 7 elements, such as fluorine, chlorine, bromine and iodine, have seven electrons in their outer shell. They are non-metals and exist as diatomic molecules (F₂, Cl₂, Br₂, I₂). They react by gaining one electron to form a negative ion with charge -1 (halide ions).
第 7 族元素，如氟、氯、溴和碘，最外层有 7 个电子。它们是非金属，以双原子分子存在（F₂、Cl₂、Br₂、I₂）。它们通过获得 1 个电子来反应，形成带 -1 电荷的负离子（卤离子）。
Reactivity decreases down the group. Fluorine is the most reactive halogen. A more reactive halogen can displace a less reactive halogen from its salt solution.
反应活性在同族中从上到下减弱。氟是最活泼的卤素。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。
Cl₂(aq) + 2KBr(aq) → 2KCl(aq) + Br₂(aq)
This displacement reaction shows that chlorine is more reactive than bromine.
这个置换反应表明氯比溴活泼。
10. Group 0 (Noble Gases) | 第 0 族（稀有气体）
Group 0 elements, also called noble gases, have a full outer shell of electrons (2 for helium, 8 for the others). This makes them very stable and unreactive. They exist as monatomic gases.
第 0 族元素，也称稀有气体，具有满电子外壳层（氦为 2，其他为 8）。这使它们非常稳定，几乎不反应。它们以单原子气体形式存在。
Their uses include:
- Helium — filling balloons and airships
- Neon — advertising signs
- Argon — providing an inert atmosphere in welding
- 氦——填充气球和飞艇
- 氖——广告灯牌
- 氩——焊接中提供惰性气氛
Because noble gases already have stable electronic configurations, they do not normally form compounds. This is an important idea when explaining why they are unreactive.
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。这是解释它们为什么不活泼时的重要概念。
Published by TutorHao | Science Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
屏轩国际教育cambridge primary/secondary checkpoint, cat4, ukiset,ukcat,igcse,alevel,PAT,STEP,MAT, ibdp,ap,ssat,sat,sat2课程辅导，国外大学本科硕士研究生博士课程论文辅导