Explain: Non-polar and polar covalent bonds.

(N/A) The existence of a $100\%$ ionic or covalent bond represents an ideal situation. In reality,no bond or compound is either completely covalent or ionic. Even in the case of a covalent bond between two hydrogen atoms,there is some ionic character.
Non-polar covalent bond: When a covalent bond is formed between two similar atoms,the shared pair of electrons is equally attracted by the two atoms. As a result,the electron pair is situated exactly between the two identical nuclei. The bond so formed is called a non-polar covalent bond.
Example: Non-polar covalent bonds in $H_2, N_2, O_2, F_2, Cl_2$.

Molecule	$H_2, N_2, O_2, F_2, Cl_2$
Bond structure	$H-H, N \equiv N, O=O, F-F, Cl-Cl$

Polar covalent bond: When atoms of two different elements (heteronuclear) combine by a covalent bond,the electron pair in the bond is attracted more by the more electronegative atom. Consequently,it acquires a partial negative charge $(-\delta)$ and the other atom acquires a partial positive charge $(+\delta)$. Such a covalent bond is called a polar covalent bond.
In an $AB$ molecule,if $A$ is less electronegative and $B$ is more electronegative,the $A-B$ bond will be $A^{+\delta}-B^{-\delta}$ (polar bond).

Molecule	$HF$	$HCl$	$CO$	$NO$
Real bond	$H^{+\delta}-F^{-\delta}$	$H^{+\delta}-Cl^{-\delta}$	$C^{+\delta} \equiv O^{-\delta}$	$N^{+\delta}=O^{-\delta}$