# Tag Info

### 5D energy levels are lower than the 4F levels for some. Why?

The reason why the 5d energy level is filled before the 4f energy level in some elements is due to the "lanthanide contraction." This contraction also causes the 5d orbitals to become lower ...
• 101
Essentially, the equation conveys how the energy of a one-electron atom varies with factors such as the nuclear charge and electronic orbit number. $-2.18\times10^{-18}\ \mathrm J$ is an empirically ...