<P> 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 cloud of electrons . Since the boundary is not a well - defined physical entity, there are various non-equivalent definitions of atomic radius . Three widely used definitions of atomic radius are: Van der Waals radius, ionic radius, and covalent radius . </P> <P> Depending on the definition, the term may apply only to isolated atoms, or also to atoms in condensed matter, covalently bound in molecules, or in ionized and excited states; and its value may be obtained through experimental measurements, or computed from theoretical models . The value of the radius may depend on the atom's state and context . </P> <P> Electrons do not have definite orbits, or sharply defined ranges . Rather, their positions must be described as probability distributions that taper off gradually as one moves away from the nucleus, without a sharp cutoff . Moreover, in condensed matter and molecules, the electron clouds of the atoms usually overlap to some extent, and some of the electrons may roam over a large region encompassing two or more atoms . </P>

What are the two factors that affect atomic radius