The cations sodium and potassium have a valence of +1 and form ionic bonds with anions. Because of their low charge density and valency, these cations are easily separated from their anions and solvate in water. Trapped by ancient seas into nascent spheroid lipid membranes, these ions are essential for cell homeostasis. Their separation across membranes establishes an electrochemical gradient that with ion pumps and exchangers function as a battery to store energy that is released and regenerated. The anion chloride balances out most of the cell sodium and potassium in ionic binding. Oxygen containing carbonates, nitrates, phosphates, and sulfates also play important roles as polyanions in combination with sodium, potassium, and divalent cations. Important divalent and trivalent cations are magnesium, calcium, iron, and copper. Variable valence atoms are important for transferring electrons in the electron transport system, for mediating catalytic activity, as cofactors in redox reactions, for carriage of O2 in muscle and blood, for intracellular signaling, and for many other functions.