Well, if we look on the chart, the first ionization energy is what is reported in your Periodic Table.

如果我们查阅图表，一级电离能,已经在元素周期表上标示了。

麻省理工公开课 - 固态化学导论课程节选

Electrons will occupy orbitals in order of ascending energy, occupying the lowest energy first and up.

电子是按其能量递增顺序,排布在轨道上的，首先占满第一级，即最低能级。

麻省理工公开课 - 固态化学导论课程节选