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

##### 1 Answer
Jun 8, 2017

By inspection?

Cuprous = copper cation with lower oxidation state, from the Latin, "cuprum"
oxide = ${\text{O}}^{2 -}$ anion

Cuprous oxide uses the old naming scheme, wherein "ous" indicates the lower oxidation state of copper. So, this is $\text{Cu"_2"O}$ (rather than $\text{CuO}$, 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, $\text{Cu"_2"O}$ 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 ${\text{H}}_{2}$, ${\text{O}}_{2}$, ${\text{F}}_{2}$, ${\text{Br}}_{2}$, ${\text{I}}_{2}$, ${\text{N}}_{2}$, and ${\text{Cl}}_{2}$ are "diatomic elements", as opposed to simply "elements".)