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{{Short description|Chemical prefix denoting the replacement of an oxygen atom with sulfur}}
{{about|the prefix in organic chemistry||Thio (disambiguation)}}

The [[Prefix (linguistics)|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'''thio-''', when applied to a chemical, such as an [[ion]], means that an [[oxygen]] atom in the compound has been replaced by a [[sulfur]] atom.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]] {{chem2|R\sO\sR′}}, 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 {{chem2|R\sS\sR′}}, where S is a sulfur atom covalently bonded to two organic groups.<ref>{{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 {{ety|grc|[[wiktionary:θεῖον|''θεῖον'']] (theîon)|sulfur}} (which occurs in Greek [[epic poetry]] as {{langx|grc|θέ(ϝ)ειον|théweion|label=none}} and may come from the same root as [[Latin]] {{lang|la|fumus}} ([[Proto-Indo-European language|Indo-European]] ''dh-w'') and may have originally meant "[[fumigation]] substance".)

==Examples==
* [[Thioamide]]
* [[Thiocyanate]]
* [[Thioether]]
* [[Thioketone]]
* [[Thiol]]
* [[Thiophene]]
* [[Thiourea]]
* [[Thiosulfate]]

==See also==
* [[Organosulfur compounds]]
* [[IUPAC nomenclature of organic chemistry]]

==References==
{{reflist}}

==External links==
*{{wti}}

{{Orgchemsuffixes}}

[[Category:Chemistry prefixes]]
[[Category:Prefixes]]