The Electron Pair Repulsion Theory states that electron pairs arrange themselves around a central atom so that the repulsion between them is a minimum.Lone pair-lone pair repulsion > lone pair-bond pair repulsion > bond pair-bond pair repulsionShapes depend on the number of lone pairs and bonding pairs. CH4 with 4 bonding pairs is tetrahedral with a bond angle of 109.5°. Ammonia has a lone pair and 3 bonding pairs and is trigonal pyramidal. The lone pair pushes the bonds closer together giving a bond angle of 107°. Water has 2 lone pairs so the bond angle is pushed further to 104.5° and the shape is non-linear or bent.