Editing Van der Waals radius (section)

== van der Waals volume ==
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The '''van der Waals volume''', ''V{{sub|w}}'', also called the '''atomic volume''' or '''molecular volume''', is the atomic property most directly related to the van der Waals radius.<ref>{{Cite web |title=Van der Waals Radii of Elements |url=https://physlab.org/wp-content/uploads/2016/03/Franck_ref2.pdf}}</ref> It is the volume "occupied" by an individual atom (or molecule). The van der Waals volume may be calculated if the van der Waals radii (and, for molecules, the inter-atomic distances, and angles) are known. For a single atom, it is the volume of a sphere whose radius is the van der Waals radius of the atom:<math display="block">V_{\rm w} = {4\over 3}\pi r_{\rm w}^3.</math>

For a molecule, it is the volume enclosed by the [[van der Waals surface]]. 
The van der Waals volume of a molecule is always smaller than the sum of the van der Waals volumes of the constituent atoms: the atoms can be said to "overlap" when they form [[chemical bond]]s.

The van der Waals volume of an atom or molecule may also be determined by experimental measurements on gases, notably from the [[van der Waals constant]] ''b'', the [[polarizability]] ''α'', or the [[molar refractivity]] ''A''. 
In all three cases, measurements are made on macroscopic samples and it is normal to express the results as [[mole (unit)|molar]] quantities. 
To find the van der Waals volume of a single atom or molecule, it is necessary to divide by the [[Avogadro constant]] ''N''{{sub|A}}.

The molar van der Waals volume should not be confused with the [[molar volume]] of the substance. 
In general, at normal laboratory temperatures and pressures, the atoms or molecules of gas only occupy about {{frac|{{val|1000}}}} of the volume of the gas, the rest is empty space. 
Hence the molar van der Waals volume, which only counts the volume occupied by the atoms or molecules, is usually about {{val|1000}} times smaller than the molar volume for a gas at [[standard temperature and pressure]].