When electrons are not shared equally in a molecule, it's called a polar covalent bond.

Here's why:

* Covalent bond: A bond formed by the sharing of electrons between atoms.

* Polar: Having a positive and a negative end due to an uneven distribution of charge.

In a polar covalent bond, one atom attracts the shared electrons more strongly than the other. This creates a partial negative charge (δ-) on the atom that attracts the electrons more and a partial positive charge (δ+) on the other atom.

Example: Water (H₂O) has polar covalent bonds. Oxygen is more electronegative than hydrogen, so it pulls the shared electrons closer to itself, giving it a partial negative charge. The hydrogen atoms have a partial positive charge.