Lone pairs
Valence electron pairs that are not bonded to any other atom.
VSEPR
Valence Shell Electron Pair Repulsion
Linear shape
One or two bonding regions; no lone pairs
V-shaped
Two bonding regions; one or two lone pairs; always polar
Trigonal planar-shaped
Three bonding regions; no lone pairs
Trigonal pyramidal-shaped
Three bonding regions; one lone pair; always polar
Tetrahedral-shaped
Four bonding regions; no lone pair