To determine the van der Waals radius of an element, you need to get two atoms that belong to that element and get them as close as possible to each other.
At this point, you measure the internuclear distance, i.e. the distance between their two nuclei, and divide it by 2.
Remember, these atoms are not bonded, they are just very, very close to each other - as close as ppossible..not overlaping
When two atoms form a covalent bond, their electron clouds overlap. In essence, that is what a covalent bond really is - an overlap betweenorbitals.
Since a part of their electron clouds overlap, the atoms will be a littlecloser to each other. This is why, when you measure the internuclear distance between the two and divide it by 2 you get a smaller value.
