3 main postulates of vsepr theory

Postulate of vsepr are:- 1-The shape of any molecule can be explained by the repulsion between all the electron pairs that are present in the valence shell. 2- The repulsion between two lone pairs is greater than the repulsion between a lone pair and a bond pair. Presence of a lone pair on the central atom causes slight distortion of the bond angles from their ideal values. 3- The electronegativity difference between the central atom and the other atoms determines the magnitude of repulsion between the bonding pair of electrons.

Postulates of Valence Bond Theory

• The overlapping of two half-filled valence orbitals of two different atoms results in the formation of the covalent bond. The overlapping causes the electron density between two bonded atoms to increase. This gives the property of stability to the molecule.
• In case the atomic orbitals possess more than one unpaired electron, more than one bond can be formed and electrons paired in the valence shell cannot take part in such a bond formation.
• A covalent bond is directional. Such a bond is also parallel to the region of overlapping atomic orbitals.
• Based on the pattern of overlapping, there are two types of covalent bonds: sigma bond and a pi bond. The covalent bond formed by sidewise overlapping of atomic orbitals is known as pi bond whereas the bond formed by overlapping of atomic orbital along the inter nucleus axis is known as a sigma bond.

1.If the centre atom is surrounded by only bond pair,the structure and shape will be same. 2.If the centre atom is surrounded by both bond pair and lone pair the structure and shape will not be same.3.Lone pair and lone pair repulsion having bond closing tendency while bond pair -bond pair having opening tendency.