📚 The Structure of the Atom | 原子结构
Atoms are the fundamental building blocks of all matter. Understanding their structure is essential for IGCSE Edexcel Science, as it explains how elements behave, how compounds form, and how chemical reactions occur. This article explores the key concepts of atomic theory, subatomic particles, isotopes, electron arrangement, and the periodic table.
原子是构成所有物质的基本单元。理解原子结构对于 IGCSE Edexcel 科学至关重要，因为它解释了元素的行为方式、化合物的形成过程以及化学反应的发生原理。本文将深入探讨原子理论、亚原子粒子、同位素、电子排布以及元素周期表等核心概念。
1. Introduction to Atomic Theory | 原子理论简介
The idea that matter is made of tiny indivisible particles dates back to ancient Greek philosophers such as Democritus. However, the modern atomic theory began with John Dalton in the early 19th century. Dalton proposed that all matter is composed of atoms, which are tiny, hard spheres that cannot be broken down further. Each element consists of identical atoms, and compounds are formed by combining atoms of different elements in fixed ratios.
物质由微小不可分割的粒子组成这一观点可以追溯到古希腊哲学家德谟克利特。然而，现代原子理论始于 19 世纪初的约翰·道尔顿。道尔顿提出所有物质都由原子构成，原子是微小的、坚硬的实心球体，无法再被分割。每种元素由完全相同的原子组成，而化合物则是由不同元素的原子按固定比例结合而成。
Dalton's model was later refined by the discoveries of the electron, proton, and neutron. J.J. Thomson's plum pudding model suggested that atoms were spheres of positive charge with negative electrons embedded, like fruit in a cake. Ernest Rutherford's gold foil experiment then revealed that most of the mass and positive charge is concentrated in a tiny nucleus, with electrons orbiting around it. Niels Bohr further improved the model by proposing that electrons travel in fixed energy levels or shells.
道尔顿的模型后来被电子、质子和中子的发现所完善。J.J. 汤姆生的“葡萄干布丁模型”认为，原子是一个带正电的球体，负电子镶嵌其中，就像蛋糕里的水果。欧内斯特·卢瑟福的金箔实验则揭示，原子的大部分质量和正电荷都集中在一个微小的核中，电子则围绕周围运动。尼尔斯·玻尔随后改进了模型，提出电子在固定的能级或电子层中运行。
2. Subatomic Particles | 亚原子粒子
Atoms consist of three main subatomic particles: protons, neutrons, and electrons. Protons and neutrons are found in the nucleus at the centre of the atom, while electrons orbit the nucleus in shells. The table below summarises their properties.
原子由三种主要的亚原子粒子组成：质子、中子与电子。质子和中子位于原子中心的原子核内，而电子则在核外的电子层中运动。下表总结了它们的性质。
| Particle / 粒子 | Relative mass / 相对质量 | Relative charge / 相对电荷 | Location / 位置 |
|---|---|---|---|
| Proton / 质子 | 1 | +1 | Nucleus / 核 |
| Neutron / 中子 | 1 | 0 | Nucleus / 核 |
| Electron / 电子 | 1/1836 (≈0.0005) | -1 | Shells / 电子层 |
In a neutral atom, the number of protons equals the number of electrons, so the positive and negative charges cancel each other out. The nucleus, containing protons and neutrons, accounts for nearly all the mass of the atom, yet its size is extremely small compared with the overall size of the atom. Most of the atom is empty space.
在电中性原子中，质子数等于电子数，因此正负电荷相互抵消。包含质子和中子的原子核几乎占据了原子的全部质量，但其尺寸与原子的整体大小相比却极小。原子的大部分是空的。
The identity of an element is determined by the number of protons in its nucleus, known as the atomic number. For example, any atom with 6 protons is carbon. The number of neutrons can vary, leading to isotopes, which we will discuss later. Electrons determine the chemical properties and bonding behaviour of the atom.
元素的种类由其原子核内的质子数决定，这称为原子序数。例如，任何含有 6 个质子的原子都是碳。中子数可以变化，从而形成同位素，我们将在后文讨论。电子则决定了原子的化学性质和成键行为。
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 is unique for each element and places the element in the periodic table. The mass number (A) is the total number of protons and neutrons in the nucleus. Since electrons have negligible mass, the mass number gives an approximate relative mass of the atom.
原子序数（Z）是原子核中质子的数量。它对每种元素是唯一的，并决定了该元素在周期表中的位置。质量数（A）是原子核中质子与中子数的总和。由于电子质量可忽略不计，质量数近似表示了原子的相对质量。
The standard notation for an element is: A X Z, where X is the chemical symbol. For example, 12 can be calculated by subtracting the atomic number from the mass number: neutrons = A - Z.
元素的标准表示法为：AXZ，其中 X 是化学符号。例如，12₆C 表示含有 6 个质子和 6 个中子的碳（因此 A=12）。中子数可通过质量数减去原子序数得到：中子数 = A - Z。
4. 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. For example, carbon-12 (12₆C) has 6 neutrons, while carbon-14 (14₆C) has 8 neutrons. Both still have 6 protons, so they are chemically identical.
同位素是属于同一种元素但中子数不同的原子。也就是说，它们具有相同的原子序数，但质量数不同。例如，碳-12（12₆C）有 6 个中子，而碳-14（14₆C）有 8 个中子。两者同样都有 6 个质子，因此化学性质完全相同。
Isotopes can be stable or unstable. Unstable isotopes undergo radioactive decay, emitting radiation to become more stable. The relative atomic mass of an element shown on the periodic table is an average of the masses of its naturally occurring isotopes, weighted according to their abundance.
同位素可分为稳定同位素和不稳定同位素。不稳定同位素会发生放射性衰变，放出辐射而变得更稳定。元素周期表中显示的元素相对原子质量，是其天然存在的同位素按照丰度加权后的平均质量。
For example, chlorine consists of about 75% 35₁₇Cl and 25% 37 5 × 0.75) + (37 × 0.25) = 35.5. This is the value typically used in chemical calculations.
例如，氯含有大约 75% 的 35₁₇Cl 和 25% 的 37₁₇Cl。其相对原子质量计算为：(35 × 0.75) + (37 × 0.25) = 35.5。这就是化学计算中通常使用的数值。
5. Electron Configuration | 电子排布
Electrons are arranged around the nucleus in specific energy levels, also called shells. The first shell can hold up to 2 electrons, the second shell up to 8, and the third shell up to 8 in the IGCSE syllabus (for elements up to calcium). Electrons fill the lowest energy level first before occupying higher ones.
电子围绕原子核在特定的能级（也称为电子层）中排布。第一层最多容纳 2 个电子，第二层最多容纳 8 个，在 IGCSE 大纲范围内第三层最多容纳 8 个（适用于到钙为止的元素）。电子先填充最低能级，再占据更高的能级。
The electron configuration can be written as a series of numbers, e.g., sodium (atomic number 11) has the configuration 2,8,1. This means 2 electrons in the first shell, 8 in the second, and 1 in the third. The outermost shell electrons are called valence electrons and they are responsible for an element's chemical reactivity.
电子排布可以写成一系列数字，例如钠（原子序数 11）的排布为 2,8,1。这表示第一层有 2 个电子，第二层有 8 个，第三层有 1 个。最外层的电子称为价电子，它们决定了元素的化学反应性。
A full outer shell makes an atom particularly stable. The noble gases (Group 0) have full outer shells, which is why they are unreactive. Other elements tend to lose, gain, or share electrons to achieve a full outer shell — this is the basis of ionic and covalent bonding.
最外层全满会使原子特别稳定。稀有气体（第 0 族）具有全满的最外层，因此它们不活泼。其他元素则倾向于失去、获得或共用电子以达到全满的最外层——这就是离子键和共价键形成的基础。
6. Ions and Charge | 离子与电荷
When an atom loses or gains electrons, it becomes an ion. Loss of electrons produces a positively charged ion, called a cation. Gain of electrons produces a negatively charged ion, called an anion. The charge of the ion depends on the number of electrons transferred.
当原子失去或获得电子时，就会变成离子。失去电子会产生带正电的离子，称为阳离子。获得电子则产生带负电的离子，称为阴离子。离子的电荷取决于转移的电子数。
For example, a sodium atom (Na) has 11 protons and 11 electrons. When it loses one electron, it becomes Na⁺ with 11 protons and only 10 electrons, giving a +1 charge. A chlorine atom (Cl) has 17 protons and 17 electrons; gaining one electron makes it Cl⁻ with 18 electrons and a -1 charge.
例如，钠原子（Na）有 11 个质子和 11 个电子。当它失去一个电子时，变成 Na⁺，有 11 个质子和仅 10 个电子，带 +1 电荷。氯原子（Cl）有 17 个质子和 17 个电子；获得一个电子后成为 Cl⁻，有 18 个电子，带 -1 电荷。
The charge on an ion is often indicated with a superscript after the symbol, e.g., Ca²⁺, O²⁻. Ions are formed because atoms want to achieve the stable electron configuration of a noble gas, which usually involves having eight electrons in the outer shell (the octet rule). Metals tend to lose electrons, while non-metals tend to gain electrons.
离子的电荷通常在符号后用上标表示，例如 Ca²⁺、O²⁻。离子之所以形成，是因为原子希望达到稀有气体的稳定电子排布，这通常意味着最外层具有八个电子（八隅体规则）。金属倾向于失去电子，而非金属倾向于获得电子。
7. Introduction to the Periodic Table | 元素周期表简介
The periodic table arranges elements in order of increasing atomic number. Elements with similar chemical properties are placed in the same vertical columns, called groups. Horizontal rows are called periods. The period number tells you the number of occupied electron shells in an atom.
元素周期表按照原子序数递增的顺序排列元素。化学性质相似的元素被放置在同一纵列中，称为族。横排称为周期。周期数表示原子中已占据的电子层数。
There are eight main groups (I–VII and 0). Group I elements (alkali metals) have one electron in their outer shell, making them highly reactive. Group VII elements (halogens) have seven electrons in their outer shell and are also very reactive. Group 0 (noble gases) have a full outer shell, making them unreactive. The transition metals are found in the central block, and they often form coloured compounds and have variable oxidation states.
共有八个主族（I 至 VII 族以及 0 族）。第 I 族元素（碱金属）最外层有一个电子，使它们极为活泼。第 VII 族元素（卤素）最外层有七个电子，也非常活泼。第 0 族（稀有气体）具有全满的最外层，因而很不活泼。过渡金属位于中间区域，它们常形成有色化合物并具有可变的氧化态。
The relative atomic mass generally increases across a period and down a group. The metallic character decreases from left to right across a period, so metals are on the left and non-metals on the right. The periodic table is an invaluable tool for predicting an element's properties and behaviour.
相对原子质量通常沿着周期从左到右以及沿族从上到下面增加。金属性沿着周期从左到右减弱，因此金属位于左侧，非金属位于右侧。周期表是预测元素性质和行为的重要工具。
8. Trends in the Periodic Table | 周期表内的变化趋势
Several important trends can be observed in the periodic table that link directly to atomic structure. Reactivity in Group I increases as you go down the group because the outer electron is further from the nucleus and more easily lost. For Group VII, reactivity decreases down the group because the attraction for an incoming electron becomes weaker as the atom gets larger.
周期表中可以观察到若干与原子结构直接相关的重要趋势。第 I 族中，自上而下反应性增强，因为外层电子离核更远，更容易失去。而对第 VII 族而言，从上到下反应性减弱，因为随着原子变大，对获取电子的吸引力变弱。
The atomic radius (size of the atom) generally increases down a group because additional electron shells are added. Across a period, atomic radius decreases due to the increasing nuclear charge pulling the electrons closer. This also explains trends in ionisation energy, which is the energy required to remove an electron from an atom.
原子半径（原子的大小）通常沿族从上到下增大，因为增加了新的电子层。沿周期从左到右，原子半径减小，因为核电荷增加，将电子拉得更近。这同样可以解释电离能的变化趋势，电离能是从原子中移除一个电子所需的能量。
In IGCSE Edexcel Science, pupils are expected to identify and describe these trends and link them to the number of shells and the nuclear attraction. The concept of 'shielding' by inner electrons also helps to explain why outer electrons are held less tightly in larger atoms.
在 IGCSE Edexcel 科学课程中，学生需要识别并描述这些趋势，并将其与电子层数以及核吸力联系起来。内层电子的“屏蔽”效应也有助于解释为什么较大原子中的外层电子被束缚得较松。
9. Summary and Key Points | 总结与要点
To recap, atoms contain protons, neutrons, and electrons. The number of protons defines the element. The mass number is the sum of protons and neutrons. Isotopes are variants of an element with different neutron numbers. Electrons are arranged in shells, and the outer shell configuration determines chemical reactivity. Ions form when atoms gain or lose electrons to achieve a full outer shell.
概括来说，原子包含质子、中子和电子。质子数定义了元素种类。质量数是质子与中子数之和。同位素是中子数不同的同一元素变体。电子分层排布，最外层的构型决定了化学活泼性。原子通过得失电子形成离子，以达到全满外层。
The periodic table organises elements by atomic number and reveals patterns in properties. The atomic number tells you the number of protons and also the number of electrons in a neutral atom. Understanding atomic structure enables you to predict bonding, compound formation, and the results of chemical reactions.
元素周期表按原子序数组织元素，并揭示了性质上的规律。原子序数告诉你质子数，也揭示了中性原子中的电子数。理解原子结构使你能够预测键合方式、化合物的形成以及化学反应的结果。
Key vocabulary to master includes: atomic number, mass number, isotope, ion, electron shell, valence electron, group, period, and relative atomic mass.
需要掌握的的关键词汇包括：原子序数、质量数、同位素、离子、电子层、价电子、族、周期以及相对原子质量。
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