3.9 What does atomic radius and ionic radius really mean to you?
Atomic radius is the distance between from the centre of an atom to the outer most shell containing the electrons. It is a measure of the size of an atom.
They can be of types like :
(a) Covalent radius, where it is the half of the distance between the line joining the centres of nuclei of two adjacent similar atoms.
(b) Metallic radius is half of the distance between the centres of the nuclei of two adjacent atoms in the metallic crystal.
(c) van der Waal's radius, half of the internuclear distance between 2 similar adjacent atoms.
Whereas, the Ionic radius is the distance from the centre of the nucleus of the ion up to which it exerts its influence on the electron cloud of an ion (cation or anion). Generally, cation has a smaller ionic radius than the parent atom and anions are larger than the parent atom.