Covalent bond/ definition, types, properties, and examples

 COVALENT BOND

Definition

          A covalent bond is formed by the mutual sharing of electrons between two atoms. This bond is formed between the atoms which have less electronegativity difference. The shared pair is equally distributed between the atoms.

Properties of covalent

1.    The melting and the boiling point of compounds in which a covalent bond is present is relatively low because week intermolecular forces present between the atoms of molecules.

2.    The rate of the reaction of covalent compounds is very slow as compared to ionic compounds.

3.The dielectric constant value of these compounds is very low.

4.    This bond is formed by the sharing of electrons between the atoms.

5. Covalent compounds do not have ions, they do not conduct electricity.

6. The atom which forms covalent bonds must have similar ionization energy and electron affinity values.

7.    Polar covalent compounds easily dissolve in water but non-polar covalent compounds dissolve only in non-polar solvents like benzene, and ether, etc.

8.    Covalent compounds show resonance and make different electronic structures.

9.Covalent bond has directional character.

10.  Covalent compounds have a definite shape on which their rate of reactions depends.

Types of covalent on the basis of pair of electrons

          On the basis of number of electrons paired shared, a covalent bond is divided into three types;

   Single covalent bond

   Double covalent bond

   Triple covalent bond

Single covalent bonds

          The bond which is formed by the share of one electron pair (2 electrons) is known as a single covalent bond. The bond is known as sigma bond (It is formed by head to head overlap of atomic orbitals).

Examples:  Cl₂, CH_4, CH₃-CH_3, NH₃, HCl

single covalent bond

Double covalent bond

          The bond which is formed by the sharing of two-electron pairs (4 electrons) is known as a double covalent bond. One sigma and one pi bond is formed in this case.

Examples:  O₂, C₂H_4, SO₂  

double covalent bond

Triple covalent bond

          The bond which is formed by the sharing of three electron pairs (6 electrons) is known as a triple covalent bond. One sigma and two pi bonds are formed in this case.

Examples: C₂H₂, N₂

triple covalent bond

Types of covalent bond on the basis of polarity

          On the basis of electronegativity difference between two atoms covalent compounds have divided into two types;

   Polar covalent compounds

   Non-polar covalent compounds

Polar covalent compounds

          If the electronegativity difference between the atoms is above 1 and below 1.7 then a polar covalent bond is formed between these atoms. In this bond shared pair is shifted more towards more electronegative atom and partial negative charge come on more electronegative atom and partial positive charge come on the less electronegative atom.

Examples: HCl, H₂O, CHCl₃ /

polar compound

Non-polar covalent compounds

          If the electronegativity difference between the atoms is below 1 then these compounds are known as non-polar covalent compounds.

Examples: CH_4, CH₃-CH₃ O₂, C₂H_4, SO₂ 

structure of methane