IMPORTANT POINTS FOR MCQS

Theories of covalent bond

Valence Shell Electron Pair Repulsion Theory: -

This theory was presented by Nyholm and   Gillespie

☻;According to them all the valence electron of the central atom are involved in the geometry of the molecule.

☻ There are two types of electrons around the central atom i.e. bonded electrons and lone pair.

☻; These electrons are arranged in space around the central atom at maximum distance from each other as to minimize the repulsion between them.

☻; Lone pair electrons and multiple bond (double & triple) electrons occupy more space than         bonded electrons.

☻The repulsion order between the different electrons are in the following order

Lone pair – Lone pair > Lone pair – Bond pair > Bond pair – Bond pair

☻; We will consider the multiple bonds as single electron pair for the purpose of VSEP repulsion theory.

Why lone pair electrons occupy more space than bond pair electrons.

As bond pair electrons are attracted by two nuclei while lone pair electrons are attracted by one nucleus.  Therefore, lone pair electrons spread its electron density more in space than that of bond pair & non bonding electrons exert more repulsive force on bonding      electrons pairs.

Application of VSEPR Theory.

            The following examples will help to explain the theory: -

(1)Molecules containing two bonded electrons pairs.  e.g. BeCl₂, HgCl₂, MgCl₂.

The, only possible geometry for BeCl₂ is linear. 

                                               

       

(2);Molecules containing three electron pairs (All are bonded) e.g. BF₃, BCl₃, AlCl₃

the geometry for such molecule will be Trigonal planer.

¥          The angle between the bonded electron will be 120^o

¥          Group IIIA are formed these compounds; the geometry of BF₃ , BCl₃

(3); Molecules containing three electron pairs (Two are bonded and one is lone pair) e.g. SnCl₂ or SO₂; the geometry of such molecules will V shaped or angular. The angles between bonded electrons will be less than 120⁰

(4)        Molecules containing four electron pairs (All are bond) e.g. CH₄, CCl₄, and S₁H₄.

The geometry for such molecules will be tetrahedral geometry. All the angles between the bonded electrons will be 109.5^O.  .

(5)        Molecules containing four pairs of electrons (one is lone pair) e.g. NH₃, PH₃.

The geometry of such molecules are pyramidal , the angles between the bonded electrons will be 107.5⁰

(6)        Molecules containing four pair of electrons (Two are bonded and two are lone pair) like H₂O, H₂S & H₂Se.

The geometry will be V shaped or angular, and the angles between the bonded electrons will be 104.5⁰.