Thio-
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The prefix thio-, when applied to a chemical, such as an ion, means that an oxygen atom in the compound has been replaced by a sulfur atom. This term is often used in organic chemistry. For example, from the word ether, referring to an oxygen-containing compound having the general chemical structure Template:Chem2, where R and R′ are organic functional groups and O is an oxygen atom, comes the word thioether, which refers to an analogous compound with the general structure Template:Chem2, where S is a sulfur atom covalently bonded to two organic groups.<ref>Template:JerryMarch</ref> A chemical reaction involving the replacement of oxygen to sulfur is called thionation or thiation.
Thio- can be prefixed with di- and tri- in chemical nomenclature.
The word derives Template:Ety (which occurs in Greek epic poetry as Template:Langx and may come from the same root as Latin {{#invoke:Lang|lang}} (Indo-European dh-w) and may have originally meant "fumigation substance".)