Most intermolecular interactions are fairly weak relative to a covalent bond. Covalent bonds typically involve energies on the order of 100 kilocalories per mole (a unit of energy commonly used in chemistry). Van der Waal’s interactions are the weakest type of intermolecular interaction with typical energies of roughly 0.01 to 1 kilocalories per mole (or 0.01% to 1% the strength of a covalent chemical bond) for a pair of interacting atoms. The strengths of ion-ion and ion-dipole interactions can vary widely, particularly in solutions, because the ions and/or dipoles can be separated by very different distances. The charges of ions can also be significantly shielded by solvent molecules around them. If the ions are very close together (like in a solid), their interaction energy can approach (or even exceed) that of a covalent bond. Hydrogen bonds are usually the strongest type of intermolecular interaction with energies of about 2–5 kilocalories per mole (or roughly 2% to 5% the strength of a covalent bond). Because they are such strong interactions, hydrogen bonds can play a dominant role in determining the structures of liquids, solids, and single molecules.