Question

How could the atomic radius of a noble gas be compared with the other elements in a period?

Answer 1

In a period, except noble gas atoms, all other atoms tend to complete their valence shell. The atomic radius of all other atoms can be measured as half the value of internuclear distance between the atoms in a combined state. On the other hand, noble gases have only weak van der Waals forces between them, due to which they have large internuclear distance between them. Also, since the valence shell of the noble gases is completely filled, therefore, there is electronic repulsion between the electrons in the valence shell which increases the size of the noble gas atoms. So, the atomic radius of noble gases has higher value than that of other elements in a period.