Why are the subscripts in a chemical formula whole numbers (for example, #N_2O_5# instead of #NO_2.5#)?

1 Answer
Truong-Son N.
Oct 2, 2016

Because it doesn't make sense to have half an atom. #"NO"_2.5#, which we could call a "pseudo-formula", implies you have (two and a) half oxygen atoms for every molecule of "#"NO"_2.5#", which is physically impossible. So, we scale to whole numbers and rewrite as #"N"_2"O"_5# instead.

Same thing with something like #"C"_1.5"H"_4"O"_0.5#. We instead write #"C"_3"H"_8"O"#.

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