Atomic Structure and the Periodic Table | 原子结构与元素周期表

📚 Atomic Structure and the Periodic Table | 原子结构与元素周期表

In this revision article, we will explore the core ideas of atomic structure and the periodic table that every Edexcel IGCSE Science student must master. We will look at the evidence for the atom, the properties of the subatomic particles, how isotopes are written, and how electron configurations control chemical behaviour. This knowledge is assessed throughout the Edexcel IGCSE Science (Double Award) papers, and it provides the foundation for all of chemistry.

在本篇复习文章中，我们将深入探讨 Edexcel IGCSE 科学考试中关于原子结构和元素周期表的核心概念。我们会了解原子模型的发现证据、亚原子粒子的性质、同位素的书写方法，以及电子排布如何决定元素的化学行为。这些知识在 Edexcel IGCSE 科学（双奖）的全部试卷中都会出现，是学习化学的基础。

1. The History of the Atom | 原子模型的历史

The idea of the atom has changed over centuries. John Dalton proposed that everything is made of tiny, indivisible spheres. Later, J.J. Thomson discovered the electron and suggested the ‘plum pudding’ model, where negative electrons were scattered inside a positive sphere.

原子模型经历了数百年的演变。约翰·道尔顿提出万物由不可再分的微小球体构成。后来，J.J. 汤姆逊发现了电子，并提出了”葡萄干布丁”模型，认为带负电的电子散布在带正电的球体中。

In 1909, Ernest Rutherford performed the gold-foil experiment. He fired alpha particles at a very thin gold foil. Most alpha particles passed straight through, but a few were deflected and a few bounced back. This showed that the atom is mostly empty space and has a tiny, dense, positive nucleus.

1909 年，欧内斯特·卢瑟福进行了金箔实验。他用 α 粒子轰击极薄的金箔。大部分 α 粒子直接穿过，少数发生偏转，极少数反弹回来。这说明原子内部大部分是空的，并且存在一个极小、致密、带正电的原子核。

Niels Bohr then placed electrons in fixed orbits around the nucleus. Later, James Chadwick discovered the neutron, a neutral particle with a mass similar to a proton, which explained the extra mass in the nucleus.

随后，尼尔斯·玻尔提出电子在原子核外的固定轨道上运动。后来，詹姆斯·查德威克发现了中子——一种质量和质子相近但不带电的粒子，从而解释了原子核中多余的质量。

2. Subatomic Particles | 亚原子粒子

An atom is made of three types of particles: protons, neutrons and electrons. Protons and neutrons are found in the nucleus, while electrons move in shells around the nucleus. The number of protons is unique to each element, and the number of electrons in a neutral atom equals the number of protons.

原子由三类粒子构成：质子、中子和电子。质子和中子位于原子核内，而电子在核外的电子壳层中运动。质子数对每种元素都是唯一的；在电中性的原子中，电子数等于质子数。

The relative mass and relative charge of each particle are shown in the table below.

每种粒子的相对质量和相对电荷如下表所示。

Notice that the electron is extremely light. The mass of a proton is 1.67 × 10⁻²⁷ kg, and the electron is about 9.11 × 10⁻³¹ kg. In exam questions, you do not need to recall these exact numbers, but you must know that protons and neutrons have roughly equal mass and that electrons have almost no mass.

注意电子非常轻。一个质子的质量约为 1.67 × 10⁻²⁷ kg，而电子约为 9.11 × 10⁻³¹ kg。考试中你不需要记住这些精确数值，但必须知道质子和中子的质量大致相等，而电子的质量几乎可以忽略不计。

3. Atomic Number and Mass Number | 原子序数与质量数

In the symbols used in IGCSE Science, two numbers are written next to the element symbol X. The atomic number Z is written as a subscript at the bottom left; it tells us the number of protons. The mass number A is written as a superscript at the top left; it tells us the total number of protons plus neutrons.

在 IGCSE 科学使用的元素符号中，元素符号 X 旁边有两个数字。左下方的原子序数 Z 代表质子数；左上方的质量数 A 代表质子数与中子数之和。

ᴬ₂X 例如 ¹⁴₆C

For example, carbon-12 is written as ¹²₆C. This tells us that a carbon atom has 6 protons and 12 − 6 = 6 neutrons. In an atom, the number of protons equals the number of electrons, so the overall charge is zero.

例如，碳-12 写作 ¹²₆C。这表示一个碳原子有 6 个质子和 12 − 6 = 6 个中子。在原子里，质子数等于电子数，因此整个原子呈电中性。

The number of protons defines the element. If a particle has 6 protons, it must be carbon; if it has 8 protons, it must be oxygen. The number of neutrons can vary without changing the identity of the element, which leads to isotopes.

质子数决定了元素的种类。如果某粒子含有 6 个质子，它一定是碳；如果含有 8 个质子，则一定是氧。中子数可以变化，但不会改变元素的归属，这就产生了同位素。

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 the neutron numbers differ, the mass numbers are different. The chemical properties of isotopes are identical because they have the same electron configuration.

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。由于中子数不同，它们的质量数也不同。同一种元素的不同同位素具有相同的化学性质，因为它们的电子排布相同。

For example, hydrogen exists as ¹₁H, ²₁H and ³₁H. Each has one proton, but they contain 0, 1 and 2 neutrons respectively. These are sometimes called protium, deuterium and tritium.

例如，氢存在 ¹₁H、²₁H 和 ³₁H 三种形式。它们都有 1 个质子，但分别含有 0、1 和 2 个中子。它们有时也被称为氕、氘和氚。

Isotopes behave the same chemically because they have the same electron configuration. However, the extra neutrons make them heavier, so physical properties such as density and rate of diffusion may differ slightly. Carbon-14 (¹⁴₆C) is radioactive and is used in archaeological dating, while the stable isotope carbon-12 (¹²₆C) is used as the standard for the

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