Atomic size is the distance between the centre of the nucleus of an atom and its outermost shell.
The shortest distance between the atom’s nuclei and the outermost shell of the atom.
The shortest distance between an atom’s nucleus and its outermost shell is known as the atomic radius.
Trends in the Periodic Table
In general, the atomic radius decreases as we move from left to right in a period and it increases when we go down a group.