Atoms can lose or gain electrons forming an ion, which has a net electric charge. A negative charged ion, called an anion (pronounced /AN-ion/), is formed when an atom or a special group of atoms gains additional electrons. When an atom loses some electrons, a positive charged ion is created called a cation (pronounced CAT-ion).
Ionic bonding takes place between two oppositely charged ions, an anion and a cation. Ions may consist of a single atom or multiple atoms, in which a group of atoms is called a "polyatomic ion." Examples of polyatomic anions include: carbonate ion, which is composed of carbon and oxygen; and sulfate ion, which is composed of sulfur and oxygen. An example of a polyatomic cation is ammonium ion, which consists of nitrogen and hydrogen. Cations are usually metal atoms and anions are either nonmetals or polyatomic ions (ions with more than one atom). The attraction of the two charges holds the atoms or molecules together. Electrostatic forces hold ionic bonds together. Many compounds made up of an anion and cation will dissolve in water, so that the two ions separate in the water and make an ionic solution. Ionic solutions are used for treating and cleaning the eye.
Ionic bonding occurs between an element that is a metal and one that is a nonmetal. The majority of geological materials, such as minerals and rocks, feature ionic bonding, predominantly.
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