The principal quantum number for 4f is 6.
The principal quantum number is the energy level of an electron in a shell with the same value. In this case, the 6 refers to the sixth energy level. The higher the principal quantum number, the greater the energy required to remove an electron from its orbital.
Each shell has a different set of possible principal quantum numbers, and each shell can have more than one possible value. For example, the second shell has two possible values: 2 or 3. The third shell has three possible values: 3, 4 or 5.
Last modified: August 11, 2022