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The meaning of «ion»

An ion (/ˈaɪɒn, -ən/)[1] is a particle, atom or molecule with a net electrical charge.

The charge of the electron is considered negative by convention. The negative charge of an electron is equal and opposite to charged proton(s) considered positive by convention. The net charge of an ion is non-zero due to its total number of electrons being unequal to its total number of protons.

A cation is a positively charged ion with fewer electrons than protons while an anion is negatively charged with more electrons than protons. Because of their opposite electric charges, cations and anions attract each other and readily form ionic compounds.

Ions consisting of only a single atom are termed atomic or monatomic ions, while two or more atoms form molecular ions or polyatomic ions. In the case of physical ionization in a fluid (gas or liquid), "ion pairs" are created by spontaneous molecule collisions, where each generated pair consists of a free electron and a positive ion.[2] Ions are also created by chemical interactions, such as the dissolution of a salt in liquids, or by other means, such as passing a direct current through a conducting solution, dissolving an anode via ionization.

The word ion was coined from Greek ion, neuter present participle of ienai (Greek ἰέναι) "to go" from PIE root *ei- "to go.", cf. a kation is something that moves down (Greek kato κάτω kat-ion) and an anion is something that moves up (Greek ano ἄνω, an-ion). So called because ions move toward the electrode of opposite charge. This term was introduced (after a suggestion by the English polymath William Whewell)[3] by English physicist and chemist Michael Faraday in 1834 for the then-unknown species that goes from one electrode to the other through an aqueous medium.[4][5] Faraday did not know the nature of these species, but he knew that since metals dissolved into and entered a solution at one electrode and new metal came forth from a solution at the other electrode; that some kind of substance has moved through the solution in a current. This conveys matter from one place to the other. In correspondence with Faraday, Whewell also coined the words anode and cathode, as well as anion and cation as ions that are attracted to the respective electrodes.[3]

Svante Arrhenius put forth, in his 1884 dissertation, the explanation of the fact that solid crystalline salts dissociate into paired charged particles when dissolved, for which he would win the 1903 Nobel Prize in Chemistry.[6] Arrhenius' explanation was that in forming a solution, the salt dissociates into Faraday's ions, he proposed that ions formed even in the absence of an electric current.[7][8][9]

Ions in their gas-like state are highly reactive and will rapidly interact with ions of opposite charge to give neutral molecules or ionic salts. Ions are also produced in the liquid or solid state when salts interact with solvents (for example, water) to produce solvated ions, which are more stable, for reasons involving a combination of energy and entropy changes as the ions move away from each other to interact with the liquid. These stabilized species are more commonly found in the environment at low temperatures. A common example is the ions present in seawater, which are derived from dissolved salts.

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