# Van der Waals Radius clarifications

1. Would it be correct to say that in general, van der Waals radius decreases as we move from left to right in the periodic table?

2. The van der Waals radius of the noble gas in a period is larger than the radius of halogen that precedes it. Why is it so?

3. What is the difference between van der Waals radius for monoatomic (say neon) and non-monoatomic (say fluorine) gases?

2. & 3. There are a lot of different ways to measure the van der Waals radius of an atom, but in recent times the preferred method is to examine the crystal structure of a molecule. Using $\ce{F2}$ as an example, the crystal would be composed of fluorine molecules. if we measure the crystallographic distance between two adjacent, but non-bonded fluorine atoms and divide by two, we would have a single value that could be used to estimate the van der Waals radius for fluorine (we would probably want to measure a number of similar values for fluorine from other molecules, maybe using $\ce{CH3F, NF3, ClF,}$ etc., for example, and average them together). Our crystal might look something like the drawing below.