Valence-Shell Electron Pair Repulsion(VSEPR) Theory

            In 1940,Sidgwick and Powell first the theory of valence-shell electron pair repulsion theory and was developed by Gillespie and Nyholm later in 1957.They explain the molecular shape and bond angle more exactly.According to them,geometry of a molecule depends on the number of bonding and non bonding electron pair in a central atom so as to maintain the minimum repulsion between them.These electron pair arrange themself in one orientation of orbitals corresponding to minimum energy and attain a definite shape.
                                       The idea of correlatin between the molecular geometry and the number of valence electrons (both shared and unshared) was originally proposed in 1939 by Ryutaro Tsuchida in Japan, and was independently presented in a Bakerain Lecturein 1940 Nevil Sidgwick and Herbert Powell of the University of oxford In 1957, Ronald Gillespie and Ronald Sydney Nyhlom of University college of London refined this concept into a more detailed theory, capable of choosing between various alternative geometries.
              Rule;
    

• IF the central atom of the molecule is surrounded by only bonding electron pair and not by non bonding electron pair, the geometry of the molecule will be regular as predicted by hybridization.
• When the central atom in a molecule is surrounded by both bond and lone pair, the molecule doesnt have regular shape.
• Presence of lone pair on the central atom cause slight distortion of the bond angle from the ideal shape. The extent of repulsion between different electron pair is in the order of;                            l.p-l.p repulsion> l.p-b.p repulsion>b.p-b.p repulsion
• The magnitude of a repulsion between bonding pairs of electrons depends  on the electronegativity difference between the central atom and other atoms.
• Double bond cause more repulsion than single bond and triple bond cause more repulsion than double bond.                                                                                                                                                                     

Molecule Type	Shape[12]	Electron arrangement†[12]	Geometry‡[12]	Examples
AX2E0	Linear			BeCl2,[1] HgCl2,[1] CO2[11]
AX2E1	Bent			NO− 2,[1] SO2,[12] O3,[1] CCl2
AX2E2	Bent			H2O,[12] OF2[17]
AX2E3	Linear			XeF2,[12] I− 3,[18] XeCl2
AX3E0	Trigonal planar			BF3,[12] CO2− 3,[19] NO− 3,[1] SO3[11]
AX3E1	Trigonal pyramidal			NH3,[12] PCl3[20]
AX3E2	T-shaped			ClF3,[12] BrF3[21]
AX4E0	Tetrahedral			CH4,[12] PO3− 4, SO2− 4,[11] ClO− 4,[1] XeO4[22]
AX4E1	Seesaw (also called disphenoidal)			SF4[12][23]
AX4E2	Square planar			XeF4[12]
AX5E0	Trigonal bipyramidal			PCl5[12]
AX5E1	Square pyramidal			ClF5,[21] BrF5,[12] XeOF4[11]
AX5E2	Pentagonal planar			XeF− 5[14]
AX6E0	Octahedral			SF6,[12] WCl6[24]
AX6E1	Pentagonal pyramidal			XeOF− 5,[13] IOF2− 5[13]
AX7E0	Pentagonal bipyramidal[11]			IF7[11]
AX8E0	Square antiprismatic[11]			IF− 8, ZrF4− 8, ReF− 8
AX9E0	Tricapped trigonal prismatic (as drawn) OR capped square antiprismatic			ReH2− 9[15]

    

•       Reference:
• Dasu Paudel
• Wikipedia
• Advance Inorganic Chemistry