Ion

Ion

1. A charged atom or molecularly bound group of atoms; sometimes also a free electron or other charged subatomic particle.
   An ion pair consists of a positive ion and a negative ion (usually an electron) having charges of the same magnitude and formed from a neutral atom or molecule by the action of radiation. In spectroscopy, the degree of ionization of an atom is indicated by a Roman numeral following the symbol for the element. An un-ionized atom is indicated by the Roman numeral I, a singly ionized atom, one which has lost one electron, is indicated by II, and so on. Thus Fe IX indicates the spectrum of an iron atom which has lost eight electrons.
2. In atmospheric electricity, any of several types of electrically charge submicroscopic particles normally found in the atmosphere. Atmospheric ions are of two principle types, small ions and large ions, although a class of intermediate ions has occasionally been reported.
   The ionization process which forms small ions depends upon two distinct agencies, cosmic rays and radioactive emanations. Each of these consists of very energetic particles which ionize neutral air molecules by knocking out one or more planetary electrons. The resulting free electron and positively charged molecule (or atom) very quickly attach themselves to one or, at most, a small number of neutral air molecules, thereby forming new small ions. In the presence of Aitken nuclei, some the small ions will in turn attach themselves to these nuclei, thereby creating new large ions. The two main classes of ions differ widely in mobility. Only the highly mobile small ions contribute significantly to the electrical conductivity of the air under most conditions. The intermediate ions and large ions are important in certain space charge effects, but are too sluggish to contribute much to conductivity. The processes of formation of ions are offset by certain processes of destruction of the ions (see recombination).
3. In chemistry, atoms or specific groupings of atoms which have gained or lost one or more electrons, as the chloride ion or ammonium ion.
   Such ions exist in aqueous solutions and in certain crystal structures.

References

This article is based on NASA's Dictionary of Technical Terms for Aerospace Use