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I would like to ask about formula of phosphorus oxide(V). Should it be $\ce{P4O10}$ or $\ce{P2O5}$? Which is right when I have to write the molecular formula?

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  • $\begingroup$ Which do you think is correct and why? Please add more details as to what you have attempted in doing the problem already. $\endgroup$ – jonsca Dec 8 '13 at 14:06
  • $\begingroup$ I have no idea. I tried to check it somewhere online and I found that P2O5 is empirical and more suitable for everything is P4O10 but still not sure enough. $\endgroup$ – mazix Dec 8 '13 at 14:17
  • $\begingroup$ Note that empirical formula and molecular formula are different. Ambiguous use of "formula", which can mean two different things, causes your confusion. P2O5 is the empirical formula and P4O10 is the molecular formula. $\endgroup$ – Xiaolei Zhu Dec 8 '13 at 20:11
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The simplest types of chemical formulas are called empirical formulas, which use only letters and numbers indicating atomic proportional ratios (the numerical proportions of atoms of one type to those of other types). Molecular formulas indicate the simple numbers of each type of atom in a molecule of a molecular substance, and are thus sometimes the same as empirical formulas (for molecules that only have one atom of a particular type), and at other times require larger numbers than do empirical formulas. (Wikipedia)

For phosphorus pentoxide the molecule seems to be an adamantane-like compound with 4 phosphorus atoms.

So the correct molecular formula of the compound would be $\ce{P4O10}$.

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