Hydrogen bonding occurs between molecules when at least one contains a hydrogen atom and both molecules have a small electric charge because the molecule is polar. Polar molecules, such as water, result from one atom having a stronger pull on the shared electrons, which causes the atoms to have slight negative or positive charges. The slight positive charge of the hydrogen atoms allow them to form hydrogen bonds with the atoms in other polar molecules with slightly negative charges. Although hydrogen bonds are considered a weak attractive force, they are the strongest weak bonds (also known as “Vander Waal’s forces”) by far. As a result, hydrogen bonding is weaker than both ionic and covalent bonds. Water is strongly affected by hydrogen bonding. Because the hydrogen bonds attract water molecules to one another, water is more tightly packed in liquid form than in solid form, where the molecules are held further apart in a lattice.