Cation
A cation is an ion which, having yielded one or more electrons, carries one or more positive electric charges: conversely, one anion contains more electrons than protons. It is so called because it is attracted, during electrolysis, by the negative electrode, called cathode, in the same way as the opposing charge poles of the magnets attract. For example, the sodium ion, denoted Na +, is the sodium atom that has lost an electron. Due to the strong polarity of its molecule, water is an excellent solvent for ions. The only cation present in pure water is the oxonium ion, usually and improperly called hydronium, formed by the solvation of the proton generated during autoprotolysis. The main inorganic cations are calcium, magnesium, sodium, potassium and ammonium. Depending on the number of electrical charges, one distinguishes the monovalent, divalent, trivalent cations, etc. The monovalent cations are those of the alkali metals; the alkaline earth metals give divalent cations; the transition metals can give mono, di, tri, tetra or pentavalent cations.