Number of Electrons in Each Shell
| Shell name |
Subshell name |
Subshell max electrons |
Shell max electrons |
|---|---|---|---|
| K | 1s | 2 | 2 |
| L | 2s | 2 | 2 + 6 = 8 |
| 2p | 6 | ||
| M | 3s | 2 | 2 + 6 + 10 = 18 |
| 3p | 6 | ||
| 3d | 10 | ||
| N | 4s | 2 | 2 + 6 + + 10 + 14 = 32 |
| 4p | 6 | ||
| 4d | 10 | ||
| 4f | 14 |
An atom's electron shells are filled according to the following theoretical constraints:
- Each s subshell holds at most 2 electrons
- Each p subshell holds at most 6 electrons
- Each d subshell holds at most 10 electrons
- Each f subshell holds at most 14 electrons
- Each g subshell holds at most 18 electrons
Therefore, the K shell, which contains only an s subshell, can hold up to 2 electrons; the L shell, which contains an s and a p, can hold up to 2 + 6 = 8 electrons; and so forth. The general formula is that the nth shell can in principle hold up to 2n2 electrons.
Although that formula gives the maximum in principle, in fact that maximum is only achieved (by known elements) for the first four shells (K,L,M,N). No known element has more than 32 electrons in any one shell. This is because the subshells are filled according to the Aufbau principle. The first elements to have more than 32 electrons in one shell would belong to the g-block of period 8 of the periodic table. These elements would have some electrons in their 5g subshell and thus have more than 32 electrons in the O shell (fifth principal shell).
Read more about this topic: Electron Shell
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