📚 Atomic Structure Essentials | IGCSE 科学：原子结构精讲
Welcome to this focused revision guide on atomic structure, a core topic in your Edexcel IGCSE Science course. Understanding how atoms are built and how they behave will help you unlock many other areas of chemistry and physics.
欢迎阅读这份关于原子结构的精讲复习指南，这是 Edexcel IGCSE 科学课程的核心主题。理解原子的构成和性质，将帮助你学好化学与物理中的许多其他内容。
1. The Development of the Atomic Model | 原子模型的发展
Early thinkers imagined atoms as tiny, indivisible spheres. John Dalton’s model, from around 1803, described atoms as solid spheres that could not be split.
早期思想家曾设想原子为微小、不可再分的球体。大约在1803年，约翰·道尔顿提出的模型将原子描述为无法再分、实在的球体。
J.J. Thomson discovered the electron in 1897 and proposed the ‘plum pudding’ model, with electrons embedded in a positive sphere.
1897年，J.J. 汤姆逊发现了电子，并提出了“葡萄干布丁”模型，即电子嵌在带正电的球体中。
Ernest Rutherford’s gold-foil experiment led to the nuclear model: a tiny, dense, positive nucleus surrounded by mostly empty space.
欧内斯特·卢瑟福的金箔实验促成了有核模型：一个微小、致密、带正电的原子核，周围大部分是空的区域。
Niels Bohr refined the model by placing electrons in fixed energy levels, or shells, around the nucleus.
尼尔斯·玻尔进一步改进模型，把电子排列在原子核周围固定的能层（即电子壳层）中。
2. Subatomic Particles | 亚原子粒子
Atoms contain three types of subatomic particles: protons, neutrons and electrons. Their properties are summarised in the table below.
原子包含三种亚原子粒子：质子、中子和电子。它们的性质总结在下表中。
| Particle | Charge | Mass (relative) | Location |
| Proton | +1 | 1 | Nucleus |
| Neutron | 0 | 1 | Nucleus |
| Electron | -1 | ≈1/1840 | Electron shells |
Protons and neutrons are found in the nucleus and are sometimes called nucleons. Electrons move rapidly in the space around the nucleus.
质子和中子位于原子核中，有时也统称为核子。电子则在原子核周围的空间中快速运动。
In a neutral atom, the number of protons equals the number of electrons, so the charges balance exactly.
在电中性的原子中，质子数等于电子数，因此正负电荷恰好平衡。
3. Atomic Number and Mass Number | 原子序数与质量数
The atomic number (Z) is the number of protons in an atom. It identifies the element in the periodic table.
原子序数（Z）是原子中质子的数目，它决定了该元素在周期表中的位置。
The mass number (A) is the total number of protons and neutrons in the nucleus. It is also called the nucleon number.
质量数（A）是原子核中质子数和中子数的总和，也称作核子数。
We write a complete nuclide notation as follows: the mass number is placed as a superscript to the left of the symbol, and the atomic number as a subscript to the left.
完整的核素表示法如下：质量数写在元素符号左上角，原子序数写在左下角。
⁴₂He or ²³⁵₉₂U
For example, helium-4 has two protons and two neutrons, so its notation would be ⁴₂He.
例如，氦-4含有两个质子和两个中子，因此可表示为⁴₂He。
4. Isotopes | 同位素
Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons.
同位素是指同一种元素中原子质子数相同、中子数不同的原子。
This means isotopes have the same atomic number but different mass numbers. For example, carbon-12 (¹²C) and carbon-14 (¹⁴C) are both carbon atoms, but carbon-14 has two extra neutrons.
这意味着同位素的原子序数相同，但质量数不同。例如，碳-12（¹²C）和碳-14（¹⁴C）都是碳原子，但碳-14多出两个中子。
Because chemical properties depend mainly on the electron arrangement, isotopes of an element usually have the same chemical behaviour.
由于化学性质主要取决于电子排布，同一元素的同位素通常具有相同的化学行为。
However, their physical properties may differ slightly, such as density or rate of diffusion.
然而，它们的物理性质可能略有不同，例如密度或扩散速率。
Isotopes are used in many applications, including radiocarbon dating and medical imaging.
同位素有很多应用，例如放射性碳定年和医学成像。
5. Electron Shells and Electronic Configuration | 电子壳层与电子排布
Electrons occupy energy levels, often called shells, around the nucleus. The first shell can hold a maximum of 2 electrons, and the second shell can hold up to 8.
电子占据原子核周围的能级，通常称为电子壳层。第一壳层最多容纳2个电子，第二壳层最多容纳8个电子。
For the first 20 elements, the third shell also fills up to 8 electrons before the fourth shell begins to fill.
对于前20号元素来说，第三壳层最多填满8个电子后，第四壳层才开始填充。
Electronic configuration is written by listing the number of electrons in each shell, separated by commas or dots. For example, sodium (Na), which has 11 electrons, has the configuration 2,8,1.
电子排布是通过列出各壳层中的电子数来表示的，用逗号或圆点分隔。例如，钠（Na）有11个电子，它的排布是2,8,1。
You may also see a dot-and-cross diagram showing the shells as circles with crosses and dots for electrons.
你也可能会看到点叉图，用圆圈表示壳层，用点和叉表示电子。
In the Edexcel specification, you should be able to draw these diagrams for the first 20 elements.
在Edexcel考试大纲中，你需要能够为前20号元素画出这些示意图。
6. Determining the Number of Particles | 计算粒子数目
To find the number of neutrons in a neutral atom, subtract the atomic number from the mass number.
在电中性原子中，求中子数目时，只需用质量数减去原子序数。
neutron number = mass number – atomic number
中子数 = 质量数 – 原子序数
For example, consider the sodium atom with mass number 23 and atomic number 11. It has 11 protons, 11 electrons and 23 – 11 = 12 neutrons.
例如，钠原子质量数为23，原子序数为11。它有11个质子、11个电子和23 – 11 = 12个中子。
If the atom is an ion, the number of electrons changes. A positive ion has fewer electrons than protons; a negative ion has more electrons than protons.
如果原子成为离子，电子数目会改变。正离子拥有的电子少于质子，负离子拥有的电子多于质子。
Always check the charge when working out electron numbers for ions.
在计算离子中的电子数时，始终要注意所带的电荷。
7. Relative Atomic Mass | 相对原子质量
Relative atomic mass (ᴀᵣ) is the weighted average mass of an atom of an element, compared to 1/12 of the mass of an atom of carbon-12.
相对原子质量（ᴀᵣ）是指某元素一个原子的平均质量与碳-12原子质量的1/12相比所得的比值。
This value accounts for the natural abundance of each isotope of that element. For most elements, ᴀᵣ is not a whole number.
该数值考虑了该元素各同位素的天然丰度。因此大多数元素的ᴀᵣ并不是整数。
To calculate ᴀᵣ from isotope data, use this formula:
根据同位素数据计算ᴀᵣ，采用以下公式：
ᴀᵣ = Σ (isotopic mass × relative abundance) / total abundance
ᴀᵣ = Σ(同位素质量 × 相对丰度) / 总丰度
For example, chlorine has two common isotopes: ³⁵Cl (75%) and ³⁷Cl (25%). The relative atomic mass is (35 × 75 + 37 × 25) / 100 = 35.5.
例如，氯有两种常见同位素：³⁵Cl（占75%）和 ³⁷Cl（占25%）。其相对原子质量为(35 × 75 + 37 × 25) / 100 = 35.5。
In your exam, you may be given abundance data and asked to perform this calculation, so practice using whole numbers and percentages.
在考试中，你可能会获得丰度数据并要求计算，因此请练习使用整数和百分比进行运算。
8. The Periodic Table and Atomic Number | 元素周期表与原子序数
The modern periodic table arranges elements in order of increasing atomic number. Rows are called periods; columns are called groups.
现代元素周期表按照原子序数递增的顺序排列元素。横行称为周期，纵列称为族。
Elements in the same group have the same number of outer-shell electrons, which gives them similar chemical properties.
同一族元素的原子最外层电子数相同，因此化学性质相似。
Group 1 elements are the alkali metals, Group 2 are the alkaline-earth metals, Group 7 are the halogens and Group 8/0 are the noble gases.
第1族元素是碱金属，第2族是碱土金属，第7族是卤素，第8/0族是稀有气体。
For IGCSE, you should be able to locate an element if you know its proton number, and you should recognise the metallic and non-metallic regions of the table.
对于IGCSE，你需要能够根据质子数在周期表中找到元素，并识别金属区和非金属区。
The diagonal ‘staircase’ from boron to astatine separates metals on the left from non-metals on the right.
从硼到砹的对角“阶梯”将左侧的金属与右侧的非金属分开。
9. Ions and Ionisation | 离子与电离
Atoms are electrically neutral, but they can lose or gain electrons to form charged particles called ions.
原子是电中性的，但它们能够失去或得到电子，形成带电的粒子，称为离子。
When an atom loses one or more electrons, it becomes a positive ion (cation). For example, sodium loses one electron to form Na⁺.
当原子失去一个或多个电子时，它变成正离子（阳离子）。例如，钠失去一个电子形成Na⁺。
When an atom gains electrons, it becomes a negative ion (anion). For example, chlorine gains one electron to form Cl⁻.
当原子得到电子时，它变成负离子（阴离子）。例如，氯得到一个电子形成Cl⁻。
The number of electrons gained or lost is related to the electron configuration. Noble gas configurations are particularly stable, so atoms tend to gain or lose electrons to achieve them.
得失电子的数目与电子排布有关。稀有气体的电子排布特别稳定，因此原子往往通过得失电子来达到这种稳定排布。
Ion charges are written as superscripts after the symbol, e.g., Mg²⁺ or O²⁻. You should be able to deduce common ion charges from group numbers for simple elements.
离子电荷写在元素符号的右上角，例如Mg²⁺或O²⁻。你应该能够根据主族元素所在的族号推断出常见的离子电荷。
10. Worked Example and Exam Tips | 实战例题与考试技巧
Question: An atom of oxygen has a mass number of 16 and an atomic number of 8. Write its electronic configuration and find the number of neutrons.
例题：氧原子质量数为16，原子序数为8。写出它的电子排布，并求出中子数。
Solution: Oxygen has 8 electrons. The first shell takes 2, the second takes 6, so the configuration is 2,6. Neutron number = 16 – 8 = 8.
解答：氧有8个电子。第一壳层有2个，第二壳层有6个，所以排布为2,6。中子数 = 16 – 8 = 8。
In the exam, always state the units and use the correct notation for nuclides, for example ¹⁶₈O.
在考试中，要始终注意单位，并使用正确的核素表示法，例如¹⁶₈O。
Remember that the number of electrons in a neutral atom equals the number of protons. For ions, adjust the electron count according to the charge.
记住，电中性原子中的电子数等于质子数。对于离子，要根据所带电荷调整电子数。
Draw electron shell diagrams carefully, making sure the inner shells are filled before adding electrons to outer shells.
绘制电子壳层图时要仔细，确保内层先填满，再添加外层电子。
When calculating relative atomic mass, check whether the abundances are percentages or relative numbers, and always show your working.
在计算相对原子质量时，检查丰度是百分比还是相对数值，并且一定要写出计算过程。
Practice a wide range of past-paper questions on atomic structure; they often combine counting particles with electron configurations and periodic table positions.
多做关于原子结构的真题；这些题目常常把粒子数计算与电子排布、周期表位置结合在一起。
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