Covalent radius:

Covalent radius: It is defined as one half of the distance between the nuclei (inter nuclear distance) of two covalently bonded like atoms in a homo nuclear diatomic molecule is called the covalent radius of that.

(A) For Homo atomic Molecules: The covalent radius (r_A) of atom A in a molecule A₂ may be given as:

The distance between nuclei of two single covalently bonded atoms in homo diatomic molecules is equal to the sum of covalent radii of both the atoms.

Illustrative example (1): A given compound A₂ whose total d_A-A is 1.4 A⁰. The atomic (covalent) radius of an atom is.

Solution:  We known that

(B) For Heteroatomic Molecules: In a hetero diatomic molecules AB where the electro negativity of atoms A and B are different, the experimental values of inter nuclear distance d_A-B is less than the theoretical value (r_A +r_B).

(1) Stevenson & Schoemaker Equation (1941):

Covalent radius of heterogeneous molecule like A-B etc determine by Stevenson & Schromaker Equation, if atoms are formed different type of covalent bond i.e. on atom is more electronegative than the other combined atom. Then the covalent radius is calculated by the relation given by Stevenson & Schoemaker, given as:

For a diatomic Hetero molecule:

Bond Length (l_A-B) = r_A + r_B- 0.09(X_A-X_B)

Where X_A= Electronegativity of more electronegative atom

Where X_B= Electronegativity of less electronegative atom

Illustrative examples 

(1) The electronegativity of F and H are 4.0 and 2.1 respectively. The percentage ionic character in H and F bond is.

(2) A given compound A2 whose total dA-A is 1.4 A0. The atomic (covalent) radius of an atom is.

(3) A given compound AB whose electronegative difference is 1.9 . Atomic radius of A and B are 4 and 2 Angstroms the distance between A and B means dA-B is ?

(4)If covalent radius of A is 0.99 A0 and bond length is 1.46 A0 Calculate the covalent radius of B. XA and XB are 3.5 and 2.5 respectively.

(5) The C–C single bond length is 1.54 Angstroms and that of Cl–Cl is 1.98 Angstroms. If the electronegativity of Cl and C are 3.0 and 2.5 respectively, the C–Cl bond-length will be equal to ?

(2) Puling equation: If the electro negativities of the two atoms A and B are X_A and X_B   respectively then

                    Bond Length (d_A-B) =( r_A +r_B)-(C₁X_A-C₂X_B)

Where C₁ and C₂ are the Stevenson’s coefficients for atoms A and B respectively 

Related Questions:

(1) What are the Amphoteric metals ? gives Examples.

(2) Name of total metalloids present in periodic table ?

(3) Total numbers of elements which are liquid at normal temperature is ?

(4) What is Mendeleev's periodic table ? give important features and draw back of Mendeleev's table.

(5) What is atomic density ? give the periodicity of atomic density in periods and groups.

(6) What is atomic volume ? and what is periodicity of atomic volume in groups and periods ?

(7) Why there are 2, 8 and 8 elements in first, second and third periodic of periods table respectively ? Explain.

(8) In alkali metal group which is the strongest reducing agent in aqueous solution and why?

(9) The electron affinity of sulphur is greater than oxygen. Why?

(10) The first ionization energy of carbon atom is greater than that of boron atom, whereas reverse is true for the second ionization energy. Explain.

(11) The electronegativities of B, Al, Ga are 2.0, 1.5, 1.6 respectively. The trend is not regular. Explain.

(12) Li2CO3 decomposes on heating but other alkali metal carbonates don’t. Explain.

(13) Of all noble metals, gold has got a relatively high electron affinity. Explain.

(14) What are the increasing order of ioni radii of first group elements in water ?

(15) What are the increasing order of molar conductivity of first group elements in water ?