In this page, there is the following paragraph:

"A metallic element contains $0.6022 \times 10^{24}$ atoms per mole (Avogadro's number) and $\rho_m/A$ moles per $cm^3$, where $\rho_m$ is the mass density (in grams per cubic centimeter} and $A$ is the atomic mass of the element. Since each atom contributes $Z$ electrons, the number of electrons per cubic centimeter. $n = N / V$, is "

Isn't $\rho_m/A$ simply the number of atoms per $cm^3$, since $A$ is mass per atom? Shouldn't you need to convert to moles (divide $\rho_m/A$ by $N_A$) to get moles per $cm^3$? Do we simply use the numerical value of $A$ an not convert to $g$?


1 Answer 1


The atomic mass is either (i) the mass per atom, as measured in amu, or (ii) the mass per mole, as measured in grams. As a result, since $\rho_m$ is specified to be in grams per cubic cm (rather than amu per cubic cm), $\rho_m/A$ is the number of moles per cubic cm.

  • $\begingroup$ Gotcha, thanks. I thought it was only in amu. $\endgroup$
    – OhMuzGawd
    Commented Dec 27, 2020 at 21:16

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