📚 3.1 Constituents of the Atom | 3.1 原子的组成
Every atom is built from three types of particle: protons, neutrons and electrons. Protons and neutrons are found in the central nucleus, while electrons occupy the space around the nucleus. Understanding the charges and masses of these particles is essential for explaining atomic stability, isotopes, ions and nuclear behaviour.
每个原子都由三种粒子构成：质子、中子和电子。质子和中子位于中心的原子核内，电子则分布在原子核周围的空间。理解这些粒子的电荷和质量，是解释原子稳定性、同位素、离子以及核行为的基础。
1. Overview of Atomic Structure | 原子结构概述
Every atom is built from three types of particle: protons, neutrons and electrons. Protons and neutrons are found in the central nucleus, while electrons occupy the space around the nucleus.
每个原子都由三种粒子构成：质子、中子和电子。质子和中子位于中心的原子核内，电子则分布在原子核周围的空间。
The diameter of an atom is about 10⁻¹⁰ m, whereas a nucleus is only about 10⁻¹⁵ m across. This means the atom is mostly empty space, but the tiny nucleus contains almost all of the atom's mass.
原子的直径约为 10⁻¹⁰ m，而原子核的直径只有约 10⁻¹⁵ m。这说明原子内部绝大部分是真空，但微小的原子核却占据了原子几乎全部的质量。
In a neutral atom the number of electrons equals the number of protons, so the total negative charge balances the total positive charge. If this balance is broken, the particle is an ion.
在中性原子中，电子数等于质子数，因此总负电荷与总正电荷相互平衡。如果这种平衡被打破，该粒子就成为离子。
2. The Nucleus: Protons and Neutrons | 原子核：质子与中子
ucleons. A proton carries a charge of +1.60 × 10⁻¹⁹ C and a mass of about 1.67 × 10⁻²⁷ kg.
原子核中的质子和中子统称为核子。质子带有 +1.60 × 10⁻¹⁹ C 的电荷，质量约为 1.67 × 10⁻²⁷ kg。
A neutron has no charge and a mass only slightly larger than that of a proton. Because neutrons are uncharged, they add nuclear mass and contribute to the strong force without increasing electrostatic repulsion.
中子不带电荷，质量仅比质子略大。由于中子不带电，它们能增加原子核的质量，并为强核力作出贡献，而不会增加静电斥力。
it, u, where 1 u = 1.66 × 10⁻²⁷ kg. This unit is convenient when comparing nuclear masses.
质子或中子的相对质量约为 1 个原子质量单位 u，其中 1 u = 1.66 × 10⁻²⁷ kg。在比较原子核质量时，这个单位非常方便。
3. The Electron Cloud | 电子云
⁹ C. Their mass is about 9.11 × 10⁻³¹ kg, which is roughly 1/1836 of the mass of a proton.
电子围绕原子核运动，带有 -1.60 × 10⁻¹⁹ C 的负电荷。电子的质量约为 9.11 × 10⁻³¹ kg，大约是质子质量的 1/1836。
In AQA A-level physics, electrons are described as existing in discrete energy levels or shells around the nucleus. The arrangement of these electrons determines an element's chemical behaviour.
在 AQA A-level 物理课程中，电子被描述为存在于原子核周围分立的能级或壳层中。这些电子的排布方式决定了元素的化学性质。
Because electrons are much lighter than nucleons, they contribute very little to the total mass of an atom, but they occupy the vast majority of the atom's volume.
由于电子比核子轻得多，它们对原子总质量的贡献极小，但它们占据了原子体积的绝大部分。
4. Relative Charge and Relative Mass
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