Question

Define atomic radii , covalent radii , metallic radii ?

Answer 1

Hint: Since the atom is considered a sphere , the size of atom is given by the radius of the sphere . It is a very important property as many other properties are related to it .

 Complete step by step answer:
Atomic radii :
Atomic radius can be defined in two ways --
The distance from the centre of the nucleus to the outermost shell containing electrons .
OR
The distance from the centre of the nucleus to the point upto which the density of the electron cloud ( probability of finding the electron ) is maximum .
Covalent radii :
Covalent radii is defined as one-half the distance between the nuclei of two covalently bonded atoms of the same element in a molecule.
Hence , for a homonuclear diatomic molecule ,
$r_{\mathrm{cov}alent}={\displaystyle \frac{1}{2}}$ [Internuclear distance between two bonded atoms ]
For example , the internuclear distance between two hydrogen atoms in the $H_2$ molecule is 74 pm
Therefore the covalent radius is ${\displaystyle \frac{1}{2}}\times 74=37pm$
Metallic radii :
Metallic radii is defined as one - half the internuclear distance between the two adjacent metal ions in the metallic lattice .

Note: When we compare the three types of atomic radii ( van der Waals radii , covalent radii , metallic radii ) we find out that van der Waals radius is the longest while covalent radius of an atom is the shortest , that is , van der Waals radius > metallic radius > covalent radius .