(a) The shape of the molecule depends upon the number of electron pairs present in the valence shell around the central atom in a molecule.
(b) Pairs of electrons in the valence shell repel one another since their electron clouds are negatively charged.
(c) These pair of electrons tend to occupy such positions in space that minimize repulsion and thus maximize distance between them.
(d) If the central atom is surrounded by lone pairs(lp) as well as bond pairs(bp), then the molecule will have a distorted geometry.
(e) The relative order of repulsion between electron pairs is as follows: lp-lp>lp-bp>bp-bp.