Covalent Bond

Covalent bond:  Such bonds are formed by mutual sharing of equal number of electrons by the atoms of the molecule. The compounds having covalent bond are called covalent compounds. Covalency can be established between similar as well as in different atoms.

For example,

covalent bond

 Characteristics of Covalent Compounds

(i) These compounds are slightly soluble in water but highly soluble in organic solvents. Solubility is fit far fat concept, i.e., polar covalent compounds dissolve in polar solvent and non-polar covalent dissolve in non-polar solvents.

(ii) They are generally rigid and directional hence show isomerism.

(iii) They have low melting and boiling points. This is due to weak covalent bond, i.e., van der Waal’s force of attraction.

(iv) They are bad conductors of electricity (due to the absence of ions).

(v) They undergo molecular reactions which are quire show. They are mostly liquids or gas but when mol. Wt. is high solid nature increases.


Variable Covalency

The elements which contain d-orbitals in their valency shell configuration (e.g. S, P, Cl, Br etc.) how variable covalence. Because these elements get excited state thus the paired electrons of p-orbitals become unpaired and one or more electron (s) shift to d-orbital.

Sometimes even paired electrons of s-orbital become unpaired and exhibit more than one covalency.

For example formation of PCl_3, PCl_5; SCl_2, SCl_4, SF_6; ICl, ICl_3, ICl_5, IF_7 etc.

Covalent bonds are of two types:

(1) Non-polar covalent bonds: when a covalent bond is formed between tow atoms of the same elements such as H_2, N_2, O_2, F_2, Cl_2etc., the sharing of electrons is equal between both the atoms. Such types of the bonds are known as non-polar covalent bonds and the compounds are called non-polar compounds.

(2) Polar covalent bonds: when a covalent bond is formed between tow atoms of different electronegativities such as HF, HCl, HBr, H_2O etc., the bonded pair of electrons shifts towards the atom whose electronegativity is greater. Due to shift of the electron pairs the atom of greater electronegativity carries partial negative charge (-\delta) and other partial positive charge (+\delta). In this way two poles are created and the bond becomes partially ionic in character e.g.

\overset{+ \delta}{H} - \overset{- \delta}{F}, \overset{+ \delta}{H} - \overset{- \delta}{O} - \overset{+ \delta}{H} the electronegativity of some elements decrease as

F > O > Cl \approx N > Br > S \approx C > I > H

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