In this task, we ask you to elaborate the sentence without changing its general meaning. You can do so by explaining further the input sentence, using more precise wording, adding qualifiers and auxiliary information etc.

The atomic radius of an element is the distance between the nucleus and the edge of the electron cloud .
The atomic radius of a chemical element is a measure of the size of its atoms , usually the mean or typical distance from the center of the nucleus to the boundary of the surrounding shells of electrons .