定义Definition
电子层是原子中主量子数 n 相同的电子所处的能级组，按 n = 1, 2, 3……也称 K、L、M、N 层。离核越远的电子层能量越高，第 n 层最多容纳 2n² 个电子。
An electron shell is the set of electron levels in an atom sharing the same principal quantum number n = 1, 2, 3…, also called the K, L, M, N shells. Shells further from the nucleus are higher in energy, and shell n holds at most 2n² electrons.
结构Structure
每个电子层由若干亚层组成：K 层只有 1s，L 层有 2s、2p，M 层有 3s、3p、3d。最多容纳的电子数为 2、8、18、32……最外层电子（价电子）决定元素的化学性质，周期序数等于原子的电子层数。
Each shell is made of subshells: K has only 1s, L has 2s and 2p, M has 3s, 3p and 3d. Capacities are 2, 8, 18, 32… The outermost (valence) electrons decide an element's chemistry, and the period number equals the number of occupied shells.
实验证据Evidence
逐级电离能在电子层改变处出现大的跳跃，例如铝失去第三个电子后，第四电离能骤然增大，说明下一个电子来自更靠近原子核的内层。光电子能谱也直接显示出不同电子层的结合能。
Successive ionisation energies jump sharply where the shell changes: after aluminium loses three electrons the fourth ionisation energy rises steeply, showing the next electron comes from an inner shell. Photoelectron spectra show the binding energies of the shells directly.
年表Timeline
- 1911
巴克拉用 K、L 表示原子发出的两组特征 X 射线
Barkla labels two series of characteristic X-rays K and L
- 1913
玻尔提出电子在分立的能级上运动
Bohr proposes electrons move in discrete energy levels
- 1916
路易斯和科塞尔用电子层结构解释化学键
Lewis and Kossel explain chemical bonding with shell structure
相关公式Formulas
例题Worked example
氢原子电离能 = E_∞ − E₁ = 13.6 eV = 1312 kJ/mol；He⁺ 为 54.4 eV。
Hydrogen ionisation energy 13.6 eV (1312 kJ/mol); He⁺ 54.4 eV.