Cation
Anions and cations
"Anion" redirects here. Not to be confused with the quasiparticle Anyon.
Hydrogen atom (center) contains a single proton and a single electron.
Removal of the electron gives a cation (left), whereas the addition of an electron gives an anion (right).
The hydrogen anion, with its loosely held two-electron cloud, has a larger radius than the neutral atom, which in turn is much larger than the bare proton of the cation.
Hydrogen forms the only charge-+1 cation that has no electrons, but even cations that (unlike hydrogen) retain one or more electrons are still smaller than the neutral atoms or molecules from which they are derived.
Anion (−) and cation (+) indicate the net electric charge on an ion. An ion that has more electrons than protons, giving it a net negative charge, is named an anion, and a minus indication "Anion (−)" indicates the negative charge.
With a cation it is just the opposite: it has less electrons than protons, giving it a net positive charge, hence the indication "Cation (+)".
Since the electric charge on a proton is equal in magnitude to the charge on an electron, the net electric charge on an ion is equal to the number of protons in the ion minus the number of electrons.
An anion (−) (/ˈænˌaɪ.ən/ ANN-eye-ən, from the Greek word ἄνω (ánō), meaning "up"[12]) is an ion with more electrons than protons, giving it a net negative charge (since electrons are negatively charged and protons are positively charged).[13]
A cation (+) (/ˈkætˌaɪ.ən/ KAT-eye-ən, from the Greek word κάτω (káto), meaning "down"[14]) is an ion with fewer electrons than protons, giving it a positive charge.[15]
There are additional names used for ions with multiple charges. For example, an ion with a −2 charge is known as a dianion and an ion with a +2 charge is known as a dication.
A zwitterion is a neutral molecule with positive and negative charges at different locations within that molecule.[16]
Cations and anions are measured by their ionic radius and they differ in relative size: "Cations are small, most of them less than 10−10 m (10−8 cm) in radius.
But most anions are large, as is the most common Earth anion, oxygen.
From this fact it is apparent that most of the space of a crystal is occupied by the anion and that the cations fit into the spaces between them."[17]
The terms anion and cation (for ions that respectively travel to the anode and cathode during electrolysis) were introduced by Michael Faraday in 1834 following his consultation with William Whewell.
Natural occurrences
Ions are ubiquitous in nature and are responsible for diverse phenomena from the luminescence of the Sun to the existence of the Earth's ionosphere.
Atoms in their ionic state may have a different color from neutral atoms, and thus light absorption by metal ions gives the color of gemstones.
In both inorganic and organic chemistry (including biochemistry), the interaction of water and ions is extremely important; an example is energy that drives the breakdown of adenosine triphosphate (ATP).
Related technology
Ions can be non-chemically prepared using various ion sources, usually involving high voltage or temperature.
These are used in a multitude of devices such as mass spectrometers, optical emission spectrometers, particle accelerators, ion implanters, and ion engines.
As reactive charged particles, they are also used in air purification by disrupting microbes, and in household items such as smoke detectors.
As signalling and metabolism in organisms are controlled by a precise ionic gradient across membranes, the disruption of this gradient contributes to cell death. This is a common mechanism exploited by natural and artificial biocides, including the ion channels gramicidin and amphotericin (a fungicide).
Inorganic dissolved ions are a component of total dissolved solids, a widely known indicator of water quality.