# Molar volume:

The molar volume, symbol $V_\mathrm m$ is the volume occupied by one mole of a substance (chemical element or chemical compound) at a given temperature and pressure.

At S.T.P conditions the molar volume of any ideal gas is $\pu{22.711 dm^3}$. My question is: how can two gases with giant difference in molecular size (say $\ce{He}$ and $\ce{Fe}$) have the same volume, considering that the size difference between them is huge, shouldn't the volume they occupy also be different?

Thanks to @MaxW for pointing out a fault.

• Most of the volume in a gas is empty space, not atoms. – orthocresol Sep 10 '18 at 15:15
• You have the wrong molar volume. Since 1982, STP is defined as a temperature of 273.15 K (0 °C, 32 °F) and an absolute pressure of exactly $10^5$ Pa (100 kPa, 1 bar) which gives a molar volume of $22.711 \mathrm{dm}^3\mathrm{/mol}$. – MaxW Sep 10 '18 at 15:19
• Calculate the average volume containing a single molecule at STP. It's about 36,000 nm3 (cubic nanometers). A single simple molecule (like CO2, SF6, etc) is about 0.03 nm3, meaning that at STP a volume of gas is about 99.9999% empty space. Even if the molecule in question becomes quite large it is still effectively occupying a similarly negligible amount of physical space. – J... Sep 10 '18 at 19:13