Order of Filling of Electron States

As the periodic table of the elements is built up by adding the necessary electrons to match the atomic number, the electrons will take the lowest energy consistent with the Pauli exclusion principle. The maximum population of each shell is determined by the quantum numbers and the diagram at left is one way to illustrate the order of filling of the electron energy states. 当元素周期表通过添加必要的电子以匹配原子序数而构建时，电子将占据符合泡利不相容原理的最低能量状态。每个壳层的最大电子数由量子数和图示决定，图中所示是一种展示电子能量状态填充顺序的方式。 For a single electron, the energy is determined by the principal quantum n number and that quantum number is used to indicate the "shell" in which the electrons reside. For a given shell in multi-electron atoms, those electrons with lower orbital quantum number l will be lower in energy because of greater penetration of the shielding cloud of electrons in inner shells. These energy levels are specified by the principal and orbital quantum numbers using the spectroscopic notation. When you reach the 4s level, the dependence upon orbital quantum number is so large that the 4s is lower than the 3d. Although there are minor exceptions, the level crossing follows the scheme indicated in the diagram, with the arrows indicating the points at which one moves to the next shell rather than proceeding to higher orbital quantum number in the same shell. 对于单个电子来说，其能量由主量子数n决定，该量子数用于表示电子所处的'壳层'。在多电子原子中，给定壳层内的电子，具有较低轨道量子数l的电子能量更低，这是因为它们能更有效地穿透内层电子的屏蔽云。这些能量级由主量子数和轨道量子数用光谱学符号指定。当你到达4s能级时，轨道量子数的影响非常显著，使得4s能级低于3d。尽管有一些例外情况，但能级的交叉遵循图中所示的方案，箭头指示的是从一个壳层过渡到下一个壳层，而不是在同一壳层内增加轨道量子数。 The electron configuration for any element may be found by clicking on that element in the periodic table. The first exception to the above scheme that is encountered is chromium, where the fifth 3d electron state is occupied instead of the second 4s state. 在元素周期表中点击任一元素即可找到其电子构型。遇到的第一个例外情况是铬，其第五个3d电子态被填充，而不是第二个4s态。

Order of Filling of Electron States

As the periodic table of the elements is built up by adding the necessary electrons to match the atomic number, the electrons will take the lowest energy consistent with the Pauli exclusion principle. The maximum population of each shell is determined by the quantum numbers and the diagram above is one way to illustrate the order of filling of the electron energy states.

For a single electron, the energy is determined by the principal quantum n number and that quantum number is used to indicate the "shell" in which the electrons reside. For a given shell in multi-electron atoms, those electrons with lower orbital quantum number l will be lower in energy because of greater penetration of the shielding cloud of electrons in inner shells. These energy levels are specified by the principal and orbital quantum numbers using the spectroscopic notation. When you reach the 4s level, the dependence upon orbital quantum number is so large that the 4s is lower than the 3d. The nature of the level crossing follows the dashed line in the diagram, which shows the points at which one moves to the next shell rather than proceeding to higher orbital quantum number in the same shell.

The electron configuration of most elements can be implied from the above diagram, but not all. The electron configuration for any element may be found by clicking on that element in the periodic table. The first exception to the above scheme that is encountered is chromium, where the fifth 3d electron state is occupied instead of the second 4s state. Copper is also an exception, filling all 10 3d states rather than the second 4s state. Niobium fills the 4th 4d state before filling the second 5s state.