In which molecule does carbon express its LOWEST oxidation number: #"methane, ethane, carbon monoxide, carbon dioxide?"#

1 Answer
Jun 1, 2017

Answer:

#"Methane......"#

Explanation:

In methane we have.............. #stackrel(-IV)"CH"_4#.

For carbon dioxide, #stackrel(+IV)"CO"_2#.

In each case, the sum of the oxidation numbers equals the charge on the species, and of course we may have a neutral molecule.

And thus #stackrel(+II)"CO"#, and #stackrel(-II)CH_3OH#.

As always, to assign oxidation state, we distribute the charge to the MOST electronegative atom. When we assign oxidation numbers to carbon compounds (which is an unusual exercise), we assume that the #"carbon-carbon"# bond is broken, the electrons are shared between the carbon radicals, i.e.

#H_3C-CH_3 rarr H_3C* +*CH_3#, i.e. #stackrel(-III)CH_3#.

And thus we speak of carbon oxidation:

#CH_4, CH_3OH, H_2C(=O), HC(=O)OH, CO_2:#

#stackrel(-IV)C;stackrel(-II)C;stackrel(0)C;stackrel(+II)C; stackrel(+IV)C#......................

And for ethane, #H_3C-CH_3rarr2xxdotCH_3#, that is #stackrel(-III)C#.