* Bonds which are formed by sharing of a pair of electrons between two atoms is called covalent bonds.

*Types of covalent bond

1)single covalent bond(ALKANES)
2)double covalent bond(ALKENES)
3)triple covalent bond(ALKYNES)

1. If two atoms share one electron pair , bond is known as single covalent bond. And is represented by one dash(-).
eg. H-H
2. If two atoms share two electron pair , bond is known as double covalent bond. And is represented by two dash (=).
eg. O=O
3. If two atoms share three electron pair , bond is known as triple covalent bond. And is represented by three dash. 
eg. Nitrogen.

Covalent bonds are a type of chemical bond that occurs when two atoms share electrons in order to achieve a stable electron configuration. This sharing of electrons results in the formation of a molecule. Covalent bonds typically occur between nonmetals or between a nonmetal and a hydrogen atom.

There are three main types of covalent bonds:

1. Single covalent bond: This occurs when two atoms share one pair of electrons. It is represented by a single line between the atoms, such as in H2 (hydrogen gas) where two hydrogen atoms share one pair of electrons.

2. Double covalent bond: This occurs when two atoms share two pairs of electrons. It is represented by a double line between the atoms, such as in O2 (oxygen gas) where two oxygen atoms share two pairs of electrons.

3. Triple covalent bond: This occurs when two atoms share three pairs of electrons. It is represented by a triple line between the atoms, such as in N2 (nitrogen gas) where two nitrogen atoms share three pairs of electrons.

In addition to these types of covalent bonds, there can also be polar covalent bonds. Polar covalent bonds occur when there is an unequal sharing of electrons between atoms due to differences in electronegativity. This results in the formation of partial positive and partial negative charges within the molecule. An example of a polar covalent bond is the bond between hydrogen and oxygen in H2O (water).

Overall, covalent bonds are important in the formation of many organic and inorganic molecules, and they play a crucial role in determining the chemical properties and behaviors of substances.