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An ion ()〔("Ion" ) entry in ''Collins English Dictionary'', HarperCollins Publishers, 1998.〕 is an atom or a molecule in which the total number of electrons is not equal to the total number of protons, giving the atom or molecule a net positive or negative electrical charge. Ions can be created, by either chemical or physical means, via ionization. In chemical terms, if a neutral atom loses one or more electrons, it has a net positive charge and is known as a cation. If an atom gains electrons, it has a net negative charge and is known as an anion. An ion consisting of a single atom is an atomic or monatomic ion; if it consists of two or more atoms, it is a molecular or polyatomic ion. Because of their electric charges, cations and anions attract each other and readily form ionic compounds, such as salts. In the case of physical ionization of a medium, such as a gas, what are known as "ion pairs" are created by ion impact, and each pair consists of a free electron and a positive ion.〔 == History of discovery == The word ''ion'' is the Greek ἰόν, ''ion'', "going", the present participle of ἰέναι, ''ienai'', "to go". This term was introduced 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.〔(【引用サイトリンク】 title=Online etymology dictionary )〕 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 moved through the solution in a current, conveying matter from one place to the other. Faraday also introduced the words ''anion'' for a negatively charged ion, and ''cation'' for a positively charged one. In Faraday's nomenclature, cations were named because they were attracted to the cathode in a galvanic device and anions were named due to their attraction to the anode. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ion」の詳細全文を読む スポンサード リンク
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