September 27, 2013 Molecular Shapes Different molecules form different shapes. Shape is based on electron arrangement. By drawing Lewis structures, you can determine the shape of molecules Ex. draw the Lewis structure for water. Water is surrounded by 4 pairs of electrons. 2 pairs are involved in bonding, 2 pairs are not. If involved with bonding pairs are called: BONDING PAIRS If not involved in bonding pairs are called: LONE PAIRS Electron pairs are arranged so that they are as far away from each other as possible (like charges repel) So in water: 109.5 107.5 105.5 120 118 180 VSEPR THEORY