Divalent

Divalent

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In chemistry, a divalent ion or molecule has a valence
Valence (chemistry)
In chemistry, valence, also known as valency or valence number, is a measure of the number of bonds formed by an atom of a given element. "Valence" can be defined as the number of valence bonds...

 of two and thus can form two bonds with other ions or molecules. An older term for divalent is bivalent.

Divalent anions are atoms or radicals with two additional electrons when compared to their elemental state (that is, with 2 more electrons than protons). For instance, S2– is the sulfide
Sulfide
A sulfide is an anion of sulfur in its lowest oxidation state of 2-. Sulfide is also a slightly archaic term for thioethers, a common type of organosulfur compound that are well known for their bad odors.- Properties :...

 anion.

A divalent cation is missing two electrons as compared with the neutral atom. For instance, iron(II) or Fe2+ is the divalent cationic form of iron. Divalent cations are present in abundance in hard water
Hard water
Hard water is water that has high mineral content . Hard water has high concentrations of Ca2+ and Mg2+ ions. Hard water is generally not harmful to one's health but can pose serious problems in industrial settings, where water hardness is monitored to avoid costly breakdowns in boilers, cooling...

, for example, calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

 (Ca2+) and magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...

 (Mg2+). These ionic minerals in solution are what contribute to the properties of water which cause it to be hard, such as the formation of limescale
Limescale
Limescale is the hard, off-white, chalky deposit found in kettles, hot-water boilers and the inside of inadequately maintained hot-water central heating systems...

.