Electron shells


Electrons always occupy shells (energy levels).

The lowest energy level is always filled first - the one closest to the nucleus.

Only a certain number of electrons are allowed in each shell.
1st shell: 2 
2nd shell: 8
3rd shell: 8

Atoms are much happier when they have full electron shells.

In most atoms, the outer shell is not full and this makes the atom want…


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