Atomic Structure: Electronic Structure

Electron shells consist of shells (1,2,3…) and sub-shells (s,p,d,f).
Sub-shell types have specific number of orbitals: s=1, p=3, d=5, f=7.
Each orbital can hold two electrons spinning in opposite directions.
Sub-shells are filled from lowest to highest energy in this order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p.
Electronic structure determines an element’s chemical properties.