# How do you use a periodic table to determine the mass of 1 mol of nitrogen gas molecules?

Dec 22, 2016

The Periodic Table lists (i) the atomic symbol, (ii) the atomic number, $Z$, and (iii) the atomic mass with units of $g \cdot m o {l}^{-} 1$. You will always be issued a copy of the Periodic Table in a chemistry or physics exam.
For nitrogen, $Z = 7$, and the atomic mass is listed as $14.01 \cdot g \cdot m o {l}^{-} 1$. Since elemental nitrogen is a diatomic element, (in fact ALL the elemental gases SAVE the inert gases are diatomic, i.e. ${X}_{2}$), the mass of gaseous nitrogen is $28.02 \cdot g \cdot m o {l}^{-} 1$.
Note that you simply have to KNOW that it is $\text{dihydrogen, dioxygen, dinitrogen, difluorine, dichlorine etc}$. ${H}_{2}$, ${N}_{2}$ etc. are the standard states of these elements under standard conditions. You would not be told this normally (certainly not if you are an undergrad!).