Co-Valent Bond

   COVALENT BONDS

a) Classical concept: 

The bond is formed by mutual sharing of electrons between the atoms. The atoms involved bonding contributes equal number of electrons for mutual sharing.

i) The bond is classified as single, double or triple bond if the number of bond pair between the atom is one, two or three respectively.

ii) Covalent bond is directional in nature.

iii) Covalency is equal to the number of electron which an atom contributes for sharing.

b) Orbital overlap concept of covalent bonds:

According to this concept, the covalent bond is formed by the overlapping of half-filled atomic orbitals present in the valence shell of the atom participated in bonding.

i) Covalency is equal to the number of half-filled orbitals which it can provides for overlapping.

ii) Larger the extent of overlapping, stronger is the bond.

iii) Axial overlapping or head to head overlapping gives rise to SIGMA (σ) bond.

iv) Lateral or sidewise overlapping gives rise to pi (π) bond.

v) All single bonds are sigma bonds.

vi) Pi bond is formed in addition to sigma bonds. Double bond, thus contains one sigma bond and one pi bond while triple bond contains one sigma and two pi bonds.

vii) Pi bonds are relatively weaker than sigma bonds.

viii) The strength of head-on overlapping varies as p-p > p-s > s-s.

ix) Different type of overlap of d-orbitals can result in the formation of sigma, pi as well as delta bond.

 CHARACTERISTICS OF COVALENT COMPOUNDS

a) They exist in all the three states.

b) They have low melting and boiling points.

c) They are less soluble in polar solvent and more soluble in non-polar solvents.

d) They are generally bad conductor of electricity.

e) Their reactions are slow and molecular nature.

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