I was looking at the values for the Van der Waals radius on various elements in wikipedia and noticed that Molybdenum does not have one. I searched a bit and found this site http://www.webelements.com/periodicity/van_der_waals_radius/ which lists the elements that have a Van der Waals radius. The non-purple ones apparently do not have one. Why is that? I don't see anything in the definition of the Van der Waals radius on wikipedia which indicates that it doesn't apply to most types of elements.