The pH of solutions is an important chemical property. Oxygen is much more electronegative than hydrogen. Both shared electrons in an oxygen-to-hydrogen bond tend to spend more time with the oxygen atom than with hydrogen. Although the vast majority of water molecules remain intact in liquid water, at any given moment a few individual hydrogen atoms succumb to the pressure of the electronegative oxygen and lose their hold on both shared electrons. When this happens, the covalent bond is broken and a hydrogen ion (positive charge because it lost its electron to oxygen, shorthand = H+) is released. The remaining part of the original water molecule is called a hydroxide ion (negative charge because it kept an extra electron, shorthand = OH-). Although present at very low levels in solution, H+ and OH- ions can have enormous effects on the properties of a solution, especially when they are not in balance. In pure water, every hydroxide ion that forms creates a hydrogen ion, so there are equal numbers of anions and cations. If a solute is added to water, however, this balance can change.
