A hydrogen bond is a weak chemical bond that occurs between hydrogen atoms and more electronegative atoms, like oxygen, nitrogen and fluorine. The participating atoms can be located on the same molecule (adjacent nucleotides) or on different molecules (adjacent nucleotides on different DNA strands). Hydrogen bonds do not involve the exchange or sharing of electrons like covalent and ionic bonds. The weak attraction is like that between the opposite poles of a magnet. Hydrogen bonds occur over short distances and can be easily formed and broken. They can also stabilize a molecule.