Why are covalent bonds between hydrogen and nitrogen or oxygen polar?

The answer to your question is below

Explanation:

Covalent bonds are bonds between to atoms that share a pair of electrons, there are three kinds of covalent bonds but I'll describe only two:

Covalent non polar bond: is a covalent bond between two elements of the same element. Ex two hydrogens, two chlorine, two oxygenes, etc.

Covalent polar bond: is a covalent bond between 2 elements of different elements, for example: hydrogen and chlorine or nitrogen, they are polar because on of the element that form it is smaller than the other one, then a partial positive and a partial negative charge is formed.