定义Definition
主量子数 n 是描述原子中电子所处电子层的量子数，取正整数 1, 2, 3……n 越大，电子离核平均越远，能量越高。第 n 层最多容纳 2n² 个电子。
The principal quantum number, n, labels the shell an electron occupies and takes the values 1, 2, 3… The larger n, the further the electron is on average from the nucleus and the higher its energy. Shell n holds at most 2n² electrons.
电子层与亚层Shells and subshells
n = 1, 2, 3, 4 的电子层也称 K、L、M、N 层。第 n 层含 n 种亚层（l = 0 至 n − 1，即 s、p、d、f），共 n² 个轨道。例如 n = 3 时有 3s、3p、3d 三种亚层，共 9 个轨道、18 个电子。
Shells n = 1, 2, 3, 4 are also called K, L, M and N. Shell n contains n kinds of subshell (l = 0 to n − 1: s, p, d, f), with n² orbitals in all. For n = 3 there are 3s, 3p and 3d, nine orbitals holding 18 electrons.
与能量的关系Link to energy
氢原子中电子的能量只由 n 决定：Eₙ = −13.6 eV / n²，电子在能级间跃迁产生线状光谱。多电子原子中能量还与亚层有关，所以出现 4s 能量低于 3d 等交错现象。
In hydrogen the electron's energy depends only on n: Eₙ = −13.6 eV / n², and transitions between levels give the line spectrum. In many-electron atoms energy also depends on the subshell, which causes overlaps such as 4s lying below 3d.
年表Timeline
- 1913
玻尔原子模型引入量子化的能级 n
Bohr's model introduces quantised energy levels n
- 1926
薛定谔方程中 n 作为解的量子数自然出现
n arises naturally as a quantum number in solutions of the Schrödinger equation