📚 Energy Levels and Orbitals in Atoms | 原子中电子的能级与轨道
Understanding how electrons are arranged within atoms is fundamental to mastering chemistry. In IB Chemistry HL, the concepts of energy levels, sub-levels, orbitals, and electron configurations form the backbone of explaining periodic trends, bonding, and spectroscopy. This article provides a comprehensive yet exam-focused guide to these topics.
理解电子在原子内部的排列方式是掌握化学的基础。在 IB 化学 HL 中，能级、亚层、轨道以及电子排布的概念是解释周期性规律、化学键和光谱学的核心。本文提供一份全面且紧扣考点的学习指南。
1. The Concept of Energy Levels | 能级的概念
losest to the nucleus and has the lowest energy; as n increases, the energy of the level increases and the average distance from the nucleus also increases.
原子中的电子占据着不同的能级，通常称为主能级或电子壳层。这些能级用主量子数 n 标记，n = 1, 2, 3……第一能级（n = 1）离原子核最近，能量最低；随着 n 增大，能级能量升高，电子距原子核的平均距离也随之增大。
The maximum number of electrons that can occupy a given principal energy level is given by the equation:
Maximum electrons in level n = 2n²
though the third level can hold 18 electrons, the outermost shell of any main-group element never exceeds 8 electrons in its ground state, which is an important rule when predicting chemical behaviour.
例如，n = 1 最多容纳 2 个电子，n = 2 最多容纳 8 个，n = 3 最多容纳 18 个。尽管第三能级可容纳 18 个电子，但任何主族元素基态原子的最外层电子数都不超过 8，这是预测化学行为时的重要规则。
2. Quantum Numbers | 量子数
s from 0 to n - 1. Each value of l corresponds to a sub-level: 0 = s, 1 = p, 2 = d, 3 = f.
电子的精确状态由四个量子数描述。主量子数 n 决定主能级和轨道的相对大小。角量子数（副量子数）l 定义轨道的形状，取值范围为 0 到 n - 1 的整数。每个 l 值对应一个亚层：0 = s，1 = p，2 = d，3 = f。
The table below summarises the relationship between n, l, and the sub-levels:
| Principal quantum number n | Possible l values | Sub-levels |
| 1 | 0 | 1s |
| 2 | 0, 1 | 2s, 2p |
| 3 | 0, 1, 2 | 3s, 3p, 3d |
| 4 | 0, 1, 2, 3 | 4s, 4p, 4d, 4f |
The magnetic quantum number mₗ describes the orientation of the orbital in space and ranges from -l to +l, giving 2l + 1 possible orientations. The spin quantum number mₛ can be either +½ or -½, representing the two possible spin states of an electron.
Published by TutorHao | IB Chemistry Revision Series | aleveler.com
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