Postulates of Theories

Question 1

Postulates of Electronic theory of valency

Answer 1

1. Number of electrons lost gained or shared by an atom is the valency of the element.
   2.. Valency is determined by the number of valence electrons in the atom because only valence electrons can take part in chemical reaction.
2. The atoms of noble gases are chemically inert and atoms of other elements tend to acquire nearest noble gas configuration.
3. By bond formation, there is an overall decrease in potential energy indicating stabilization.
4. They form covalent or ionic bond to acquire nearest noble gas configuration.

Question 2

Postulates of Valence Bond Theory

Answer 2

1. A covalent bond is formed by the complete overlapping of half filled valence atomic orbital of one atom with another half filled valence atomic orbital of another atom.
2. Each valence atomic orbitals participating in the bond formation must be half filled and should have their electrons with opposite spin. Completely filled atomic orbitals do not take part in bond formation.
3. The strength of bond formed depends upon the extent of overlapping of atomic orbitals. Greater the overlapping of atomic orbitals , stronger the covalent bond formed.
4. Overlapping lowers the potential energy of the molecule in a system and excess energy is released.