Question

Postulates of vbt &vsepr

Answer 1

https://byjus.com/chemistry/valence-bond-theory/

Postulates of Valence Bond Theory:

• The overlapping of two half filled valence orbitals of two different atoms result in the formation of the covalent bond. Due to overlapping, the electron density between two bonded atoms increases and this gives 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 and it is 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.

https://byjus.com/chemistry/vsepr-theory/

Postulates of VSEPR:

1. For polyatomic molecules containing three or more atoms, one of the atoms of that molecule is called the central atom to which all the other atoms are linked.
2. The shape of a molecule depends upon the total number of valence shell electron pairs.
3. The electron pairs tend to occupy positions in space such that the electronic repulsion gets minimized and hence the distance between them is maximized.
4. The valence shell is assumed to be a sphere such that the electron pairs localize on the surface of the sphere with maximum distance between the valence shell and electron pairs.
5. If the central atom is surrounded by bond pairs then we can expect a symmetrical shape to the molecule.
6. If the central atom is surrounded by lone pairs and bond pairs both, then a distorted shape of the molecule is observed.
7. In case of resonating structures, this theory can be applied to any of them.
8. The order of repulsion between electron pairs follows the trend:
   lone pair – lone pair > lone pair – bond pair > bond pair – bond pair