ionized

Ionized describes matter whose atoms or molecules have lost or gained electrons, resulting in charged particles called ions. Ionized species carry a net positive or negative charge, and the term can refer to the process of ionization or to the resulting ions themselves. Ionization is a fundamental concept in chemistry, physics, and materials science.

Ionization occurs when sufficient energy is provided to overcome the electrostatic attraction of electrons to the nucleus. This energy input can come from heat, electrical discharge, photons, or energetic particle collisions. In atoms, removing electrons yields ions with increasing positive charge (first ionization, second ionization, etc.). Electron attachment can also form negative ions, though the term ionization more commonly describes electron removal.

In many contexts, especially in plasmas, a substantial fraction of constituent particles are ionized, creating an ionized gas or plasma. The ionization state affects electrical conductivity, chemical reactivity, and optical spectra. Ionization energy, including first and successive ionization energies, quantifies how strongly electrons are bound and how much energy is needed to remove them.

Applications span multiple fields. In mass spectrometry, ionization methods such as electrospray and matrix-assisted laser desorption generate ions for analysis. In lighting and displays, ionized gases produce characteristic emissions. In astrophysics and atmospheric science, ionization fractions influence thermal balance, chemistry, and the propagation of radiation. Neutral atoms can exist in equilibrium with ions depending on temperature, pressure, and radiation fields.

See also: plasma, ionization energy, cation, anion, mass spectrometry.