The general electronic configuration of actinides can be described in follows:
- All actinides start after radon, so they have the radon core.
- Electrons are gradually added to the 5f orbitals, from 1 to 14 electrons across the series.
- Some actinides may have electrons in the 6d orbital (0 to 2 electrons).
- The 7s orbital always has 2 electrons.
For example:
- Actinium has electrons in the radon core, one in 6d, and two in 7s.
- Thorium has electrons in the radon core, one in 6d, and two in 7s (sometimes a small contribution in 5f).
- Uranium has electrons in the radon core, three in 5f, one in 6d, and two in 7s.
In short, actinides gradually fill the 5f orbitals while keeping 7s and sometimes 6d electrons stable.