Pi (π) BOND, SHAPES PF MOLECULES AND DIFFERENT MODERN THEORIES OF COVALENT BONDING, A double covalent bond consists of one sigma

Pi (π) BOND:

             A double covalent bond consists of one sigma (a) bond and one pi (π) bond. If two atom orbital receipt s-orbital, have their axis parallel to each other and such parallel atomic orbital overlap, the resulting bonding molecular orbital is called pi (π) bond or the bond which is formed due to side to side overlapping of two atomic orbital is called pi (π) bond. Electron density in pi (π) bond is high above and below the bonded nuclear. 

SHAPES PF MOLECULES AND DIFFERENT MODERN THEORIES OF COVALENT BONDING:

 

            Bonding is key to molecular structure and the structure is ultimately related to physical and chemical properties. The description of a covalent bond as a shared pair of electrons between two nuclear does not provide much help in determining the shape and geometry of a molecule. Similarly may other properties like bond energy bond polarity, dipole moment, paramagnestism variation in melting and bonding point cannot be extained without shape of molecular presently three theories are being used presently three theories are being used to understand the nature of covalent bond.

               (1)              Valence bond theory (VGT).

(2)              Valence shell electron pair repulsion theory (VSEPRT)

(3)              Molecular orbital theory (MOT)

 THE VALENCE BOND THEORY (VBT):

             VBT explains the bonding in terms of overlapping of atomic orbitals. Formation of sigma (a) bond and pi (π) bond is also a part of valence bond theory. This theory also explains the mixing of different atomic orbitals to form new degenerate orbitals, it is called orbital hybridization or expansion of octet

 ORBITAL HYDRIDIZATION:

 

            The process in which atomic orbitals of different energy and shape are mixed together to form a new set of degenerate orbitals of same energy and same shape is called orbital hybridization.

 

WHY CONCEPT OF ORBITAL HYBRIDIZATION IS INECECESSARY:

           

            According to simple concept of valence bond theory one can expect that the number of covalent bonds which an element can form to be equal to the number of unpaired electrons in the valence shell if that element e.g;