A hydrogen bond is an intermolecular electrostatic attraction between a hydrogen atom and an electronegative atom with a lone pair of electrons. In a polar molecule, like hydrogen fluoride or HF, ammonia or NH3, and water or H2O, the fluorine, nitrogen, or oxygen atom is more electronegative than hydrogen. The more electronegative atom attracts bonding electron pairs more strongly than hydrogen. This results in unequal electron distribution in the bond, giving the electronegative atom a partial negative charge and the hydrogen atom a partial positive charge. The partial positive charge on the hydrogen atom enables it to attract non-bonded pair of electrons of an electronegative atom in its vicinity, forming a hydrogen bond. Hydrogen bonds provide structural stability to various biological molecules, including DNA.