# Why can't we calculate the atomic radii of noble gases?

My book says that only the Van der Waal's radius of noble gases can be measured as these gases generally do not form compounds (except Xenon.) Then why can't we just calculate the atomic radii by computation, say solving the Schrödinger equation? Can't we make computer simulation models of isolated atoms of noble gases?

• We can all right, but that's not what is called a measurement. – Ivan Neretin Jul 16 '17 at 6:39
• @IvanNeretin Agreed, then can't we accept the simulated model results as excatly as a measurement? – Apoorv Potnis Jul 16 '17 at 6:45
• What's to accept and what for? We won't be needing those radii anytime soon. And in any case, the book says nothing about that. It just says they can't be measured, which is true. – Ivan Neretin Jul 16 '17 at 6:50
• You can experimentally measure the atomic radii using x-ray crystallography. All form crystals except helium. – porphyrin Jul 16 '17 at 8:52
• @porphyrin Solid helium has a hexagonal crystal structure. Also there is no such thing as an "atomic radius", that is a catch-all term for vdW radius, ionic radius, covalent radius, metallic radius. en.wikipedia.org/wiki/Atomic_radius – Karl Jul 16 '17 at 14:33

Covalent radius is measured as the distance ($r_\text{cov} = d/2$) between the nuclei of two bonded atoms (covalent). But, if you try to do the same for noble gases/inert gases (good luck!), as they have fully filled $np$ orbitals, they will repel each other, hence the closest distance between the two atoms is taken (high pressure, low temperature) as the van der Waals radius.