|MadSci Network: Chemistry|
Naming of chemical compounds (nomenclature) is a necessary part of chemistry and there are large volumes which dictate how a new compound should be named. But contrary to popular belief a long name for a compound certainly isn't instantly recognisable to a chemist which is why diagrams are so valuable. For 'small' molecules the rules or perhaps the convention isn't so rigid for CCl4 both carbon tetrachloride and terachloromethane are used interchangably. It is interesting to note that CHCl3 isn't called carbon trichloride, but rather chloroform or trichloromethane (the former being the much more popular alternative) and CH2Cl2 is dichloromethane or less commonly methylene chloride. CH3Cl is usually referred to as methyl chloride. Confusing, yes. This is probaby in part due to the fact that these 'simple' compounds were discovered long before internationally accepted names were decided upon and they have become almost 'slang' words in modern chemical vocabulary. Another fine example is 'acetone' the proper name for this is 2-propanone but it is never called that, ethanoic acid is always called acetic acid. We don't use carbon(IV) chloride because in organic compounds carbon only has a stable oxidation state of -4 [so in any case it would be carbon(-IV) chloride] so there is no ambiguity. For example sodium chloride is never called sodium(I) chloride because the only stable combination of sodium and chlorine is with sodium in the +1 oxidation state. However, for something like iron chloride you have to specify either iron(II) chloride or iron(III) chloride because both are quite stable compounds. As for CS2 being called carbon disulfide, this is probably another historical relic. It is the direct analogue of carbon dioxide. It is interesting to note that if you go another row down the periodic table, CSe2 is called carbon selenide. I hope this clears up a few things. It is important to learn the conventional naming rules, it is much like learing a new language: tackle the regular verbs first and learn the irregular exceptions when you come across them! Feel free to E-mail me if you have any other questions. Dr. Scott Starling University of Sydney, Australia. firstname.lastname@example.org
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