What are the two types of covalent bonds?

The two types of covalent bonds are polar and nonpolar. 

Nonpolar covalent bonds arise when two atoms (either of the same element or different elements) share electrons equally. In oxygen, the electrons are evenly arranged between the two oxygen atoms, resulting in a nonpolar covalent bond. 

In polar covalent bonds, electrons are shared unevenly between atoms due to a stronger attraction of one nucleus compared to the other. This difference in attraction is quantified by electronegativity. Atoms with higher electronegativity are more attracted to electrons, contributing to the uneven sharing of electrons in a polar covalent bond. Also, due to the uneven sharing of electrons between atoms of different elements, a small negative charge (δ-) or a small positive charge (δ+) emerges. This partial charge is referred to as the dipole. Water is a common example of a polar covalent molecule. Since electrons are not shared equally and the molecule's shape is asymmetrical, a water molecule has two ends with different charges: a positive charge on the hydrogen side (or pole) and a negative charge on the oxygen side.