Number of electrons per layer:
The heaviest naturally-occurring element Uranium (atomic number 92) has 32 electrons in its 4th energy level the N shell. By contrast, Silicon (atomic number 14) has the maximum number of 2 electrons in its K shell, 8 in its L shell, but only 4 out of a possible 18 electrons in its outermost M shell. These outer electrons are also called valence electrons and it is these electrons that can be made to migrate from atom to atom when an electric current flows through the silicon.
The formula to calculate the maximum electron capacity per orbital = (\(2n^{2}\))
| Orbital Layer (n) | Shell Name | Max. nr of e- = 2n2 | Total nr of e- per atom |
| 1 | K | 2 | 2 |
| 2 | L | 8 | 10 |
| 3 | M | 18 | 28 |
| 4 | N | 32 | 60 |
| 5 | O | 50* (theoretically) | 110 |
| 6 | P | 72 | |
| 7 | Q | 98 |
* Even in the heaviest confirmed element on the periodic table which is man-made and decays in a fraction of a millisecond - Oganesson (atomic number 118) - the 5th shell only holds 32 electrons. To reach 50, an atom needs to start putting electrons into the 5g sublevel (which holds the remaining 18 electrons). An element would need an atomic number of 121 or higher to begin placing electrons into the 5g sublevel. Because elements that heavy are highly unstable and have not yet been successfully synthesized in a lab, a completely full 5th shell remains purely theoretical.
Sc atomic number 21:
The electron configuration for a neutral scandium atom is \(1s^2 \, 2s^2 \, 2p^6 \, 3s^2 \, 3p^6 \, 4s^2 \, 3d^1\)
