How would you prove that cuprous oxide is not an element?

1 Answer
Truong-Son N.
Jun 8, 2017

By inspection?

Cuprous = copper cation with lower oxidation state, from the Latin, "cuprum"
oxide = #"O"^(2-)# anion

Cuprous oxide uses the old naming scheme, wherein "ous" indicates the lower oxidation state of copper. So, this is #"Cu"_2"O"# (rather than #"CuO"#, cupric oxide).

But even if you didn't know that, that doesn't matter, because we know it contains two different elements. Copper has an atomic number not equal to #8#.

By definition, #"Cu"_2"O"# must therefore be a compound. An element must have a single identity and thus contain atom(s) with one consistent atomic number.

(that's why we specify that #"H"_2#, #"O"_2#, #"F"_2#, #"Br"_2#, #"I"_2#, #"N"_2#, and #"Cl"_2# are "diatomic elements", as opposed to simply "elements".)

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