Nuclear Power Plant Isar, Germany

Spent nuclear fuel pool

Turbine of a nuclear plant

Defining ion

In physics and chemistry, an ion is an atom or molecule that has a neutral electric charge. It is called cation an ion with positive charge, and an ion anion negatively charged. The process of gaining or losing electrons (relative to the neutral atom or molecule) is called ionization. They usually represent the cations and anions with the symbol for the atom and the "+" or "-" symbol, respectively. If the number of electrons gained or lost is greater than one, this is also indicated.

The cations and anions are attracted to the cathode and anode, respectively.

Michael Faraday was the first to propose the existence of ions in 1830, but was Arrhenius who developed the corresponding theory in 1884. This earned him the Nobel Prize in Chemistry in 1903.

The energy required to remove an electron from an atom in a vacuum is the ionization potential or ionization energy of that atom. Atomic ionization potentials are physical constants characteristic of each atom. The same concept can be applied to molecules and solids.

Generally, the ionization potentials decrease from top to bottom, and grow from left to right in the periodic table. This tendency is the opposite of that found for the atomic radius. This is because, in small atoms, the electrons are attracted more strongly by the core and more power to uproot.

The first ionization potential is needed to start the first electron to a neutral atom; the second potential is the one to start neceista two electrons, and so on. The ionization potentials are gradually increasing. Generally, there is considerable energy gap at some point in the series. This makes each atom tends to form a certain type of cation.

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Last review: February 1, 2016