📚 Atomic Structure | 原子结构
Understanding the structure of an atom is fundamental to all of science. This topic appears in the Edexcel IGCSE Science syllabus as a core concept that links chemistry and physics.
理解原子的结构是所有科学的基础。该主题是Edexcel IGCSE科学课程中的核心概念，将化学与物理联系起来。
1. The Atom and Its Particles | 原子及其粒子
Every element is made of tiny particles called atoms. Each atom consists of a central nucleus surrounded by electrons. The nucleus contains protons and neutrons, which are collectively called nucleons.
每种元素都由称为原子的微小粒子组成。每个原子由一个位于中心的原子核和围绕它运动的电子构成。原子核包含质子和中子，它们统称为核子。
Proton: positive charge, relative mass 1, found in the nucleus.
质子：带正电荷，相对质量为1，位于原子核内。
Neutron: neutral charge, relative mass 1, also in the nucleus.
中子：不带电荷，相对质量也为1，同样位于原子核内。
Electron: negative charge, relative mass 1/1840 (often taken as 0), moves around the nucleus in energy shells.
电子：带负电荷，相对质量约为1/1840（通常视为0），在能壳（电子层）中绕核运动。
An atom is electrically neutral because the number of protons equals the number of electrons.
原子呈电中性，因为质子数等于电子数。
2. Historical Models of the Atom | 原子模型的发展
The current model of the atom evolved over many centuries. In 1803, John Dalton proposed that atoms were solid, indivisible spheres. This was the first scientific model based on experiments.
现代原子模型经历了多个世纪的发展。1803年，约翰·道尔顿提出原子是坚实且不可再分的球体。这是基于实验的第一个科学模型。
J.J. Thomson (1897) discovered the electron and proposed the "plum pudding" model: a sphere of positive charge with embedded negative electrons.
J.J. 汤姆森（1897年）发现了电子，并提出“葡萄干布丁”模型：一个带正电荷的球体，其中镶嵌着带负电的电子。
Ernest Rutherford (1911) fired alpha particles at gold foil. Most passed through, but a few rebounded, proving that most of the atom is empty space with a tiny, dense, positive nucleus.
欧内斯特·卢瑟福（1911年）用α粒子轰击金箔。大多数粒子穿过，少数反弹，证明原子大部分是空的，且有一个微小、致密、带正电的原子核。
Niels Bohr (1913) suggested that electrons orbit the nucleus in fixed circular paths called shells or energy levels.
尼尔斯·玻尔（1913年）提出电子在固定的圆形轨道（称为壳层或能级）上绕核运动。
The modern model (quantum mechanical) treats electrons as probability clouds, but the Bohr model is sufficient for IGCSE chemistry.
现代模型（量子力学）将电子视为概率云，但在IGCSE化学中，玻尔模型已足够使用。
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 defines the element. The mass number (A) is the total number of protons and neutrons in the nucleus.
原子序数（Z）是原子中质子的数量，它确定了元素的种类。质量数（A）是原子核中质子与中子的总数。
Mass number = protons + neutrons
质量数 = 质子数 + 中子数
For example, carbon-12 has 6 protons and 6 neutrons, so its atomic number is 6 and mass number is 12.
例如，碳-12有6个质子和6个中子，所以其原子序数为6，质量数为12。
| Particle | Symbol | Relative charge | Relative mass |
| Proton | p⁺ | +1 | 1 |
| Neutron | n⁰ | 0 | 1 |
| Electron | e⁻ | -1 | 1/1840 |
4. Isotopes | 同位素
Isotopes are atoms of the same element that have the same number of protons but different numbers of neutrons. Therefore they have the same atomic number but different mass numbers.
同位素是同一元素中具有相同质子数但不同中子数的原子。因此它们具有相同的原子序数但不同的质量数。
For example, hydrogen has three isotopes: protium (¹H), deuterium (²H), and tritium (³H). All have one proton, but zero, one, and two neutrons respectively.
例如，氢有三种同位素：氕（¹H）、氘（²H）和氚（³H）。它们都只有一个质子，但中子数分别为0、1和2。
Isotopes have identical chemical properties because chemical behaviour depends on the number and arrangement of electrons. However, their physical properties may differ, such as density and rate of diffusion.
同位素具有相同的化学性质，因为化学行为取决于电子的数量和排布。然而，它们的物理性质可能不同，例如密度和扩散速率。
5. Relative Atomic Mass | 相对原子质量
The relative atomic mass (Aᵣ) of an element is the weighted mean mass of all its isotopes compared with one-twelfth the mass of a carbon-12 atom.
元素的相对原子质量（Aᵣ）是其所有同位素的加权平均质量，与碳-12原子质量的1/12相比所得的数值。
Since isotopes exist in different abundances, the weighted average is calculated from the percentage of each isotope in a natural sample.
由于同位素以不同丰度存在，加权平均值根据各同位素在自然样品中的百分比计算。
For chlorine, 75% is ³⁵Cl and 25% is ³⁷Cl.
对于氯，75%为³⁵Cl，25%为³⁷Cl。
Aᵣ = (75 × 35 + 25 × 37) / 100 = 35.5
相对原子质量 = (75 × 35 + 25 × 37) / 100 = 35.5
This is why chlorine's relative atomic mass is shown as 35.5 on the periodic table.
这就是为什么氯在周期表上的相对原子质量显示为35.5。
6. Electron Shells and Electronic Configuration | 电子层与电子排布
Electrons occupy specific energy levels (shells) around the nucleus. The first shell can hold up to 2 electrons, the second and third shells can each hold up to 8 electrons.
电子占据原子核周围特定能级（壳层）。第一层最多容纳2个电子，第二层和第三层各最多容纳8个电子。
has 2 electrons in the first shell, 8 in the second, and 1 in the third, written as 2.8.1.
电子排布按壳层占位顺序书写。例如，钠（Z = 11）第一层有2个电子，第二层8个，第三层1个，写作2.8.1。
Stability is achieved when the outer shell is full. Atoms may lose, gain, or share electrons to obtain a noble gas configuration.
当外层电子排满时达到稳定状态。原子可能失去、获得或共享电子以获得稀有气体的电子构型。
7. Ions and Ionic Bonding | 离子与离子键
When atoms lose or gain electrons, they form charged particles called ions. Metals lose electrons to form positive ions (cations); non-metals gain electrons to form negative ions (anions).
当原子失去或获得电子时，它们就形成带电粒子，称为离子。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）。
Sodium loses one electron: Na → Na⁺ + e⁻
钠失去一个电子：Na → Na⁺ + e⁻
Chlorine gains one electron: Cl + e⁻ → Cl⁻
氯获得一个电子：Cl + e⁻ → Cl⁻
Opposite charges attract and form an ionic bond, such as in sodium chloride (NaCl). In the solid state, ions are arranged in a giant lattice structure with strong electrostatic forces.
相反电荷相互吸引并形成离子键，例如氯化钠（NaCl）。在固态中，离子排列成巨大的晶格结构，具有很强的静电作用力。
8. Covalent Bonding | 共价键
Non-metal atoms can share electrons to achieve a full outer shell. The shared pair of electrons forms a covalent bond.
非金属原子可以通过共享电子来获得满壳层。共享的电子对形成共价键。
For example, water (H₂O) has two hydrogen atoms each sharing one electron with oxygen. The oxygen atom shares two of its electrons, forming two single covalent bonds.
例如，水（H₂O）中有两个氢原子分别与氧共享一个电子。氧原子共享其两个电子，形成两个单共价键。
Molecules are represented by dot-and-cross diagrams, and molecular formulas show the number of atoms of each element.
分子用电子点叉图表示，分子式显示每种元素的原子数目。
Simple covalent molecules have low melting and boiling points because the intermolecular forces are weak, even though the covalent bonds within the molecule are strong.
简单共价分子的熔点和沸点较低，因为分子间作用力较弱，尽管分子内部的共价键很强。
9. The Periodic Table | 元素周期表
The periodic table arranges elements in order of increasing atomic number. Elements in the same group (vertical column) have the same number of outer electrons and therefore similar chemical properties.
元素周期表按照原子序数递增的顺序排列元素。同一族（纵列）的元素具有相同的外层电子数，因此化学性质相似。
Group 1 (alkali metals): one outer electron, very reactive, form +1 ions.
第1族（碱金属）：有1个外层电子，非常活泼，形成+1离子。
Group 7 (halogens): seven outer electrons, form -1 ions, exist as diatomic molecules.
第7族（卤素）：有7个外层电子，形成-1离子，以双原子分子存在。
Group 0 (noble gases): full outer shell, very stable and unreactive.
第0族（稀有气体）：外层全满，非常稳定，不易反应。
Periods (horizontal rows) correspond to the number of shells used in the electronic configuration.
周期（横行）对应于电子排布中所使用的壳层数。
10. Metals and Non-metals | 金属与非金属
The periodic table is divided into metals on the left and centre, and non-metals on the right. Metals typically have high melting points, are good conductors of heat and electricity, and are malleable and ductile.
周期表左侧和中部为金属，右侧为非金属。金属通常具有高熔点，是良好的热和电的导体，并且具有延展性和可锻性。
Non-metals generally have lower melting points and do not conduct electricity (except graphite). They often form covalent compounds.
非金属通常熔点较低，不导电（石墨除外）。它们常形成共价化合物。
Metallic bonding involves a lattice of positive ions in a "sea of electrons", which explains conductivity and malleability.
金属键涉及在“电子海”中正离子构成的晶格，这解释了导电性和延展性。
Published by TutorHao | Science Revision Series | aleveler.com
更多咨询请联系16621398022（同微信）
或截图后用「扫一扫 → 相册」选择本图