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Chemical Bonding and Molecular Structure

Long Answer Type

161.

Explain coordinate bond by the orbital concept.

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162.

Differentiate between a covalent bond and co-ordinate bond.

120 Views

Short Answer Type

163.

What do you understand by geometry and shapes of molecules?

111 Views

164.

Why do covalent moleucles have definite geometery?

245 Views

Long Answer Type

165.

Name the theory responsible for the definite geometry of covalent molecules. Give main features of the theory ?

124 Views

Short Answer Type

166.

What do you mean by Regular geometry and Irregular or Distorted geometry?

435 Views

167.

How will you explain the following order of the repulsive interactions between pair of electrons on the central atom:
Lone pair - Lone pair > Lone pair - Bond pair > Bond pair - Bond pair.

173 Views

Long Answer Type

168.

On the basis of VSEPR theory, discuss the geometry of the following covalent molecules: (i) BeF₂(ii) BF₃(iii) CH₄.

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169.
With the help of VSEPR theory, explain the shape of: (i) NH₃ (ii) H₂O.

(i) NH₃Molecule: In ammonia molecule, the central nitrogen atom

has five electrons in the valence shell. Three of these electrons are mutually shared with the electrons of three hydrogen atoms to form three N- H bonds as shown.

Hence, the central N atom in NH₃ is surrounded by three bond pairs and one lone pair. The geometry expected for the molecule is tetrahedral since lone pair-bond pair repulsion is more than bond pair-bond pair repulsion. As a result, the lone pair of electrons will repel another pair strongly. Therefore three N–H bonds of NH₃ are forced slightly closer.
This leads to decrease in H – N – H bond angles from a normal angle of a tetrahedron (109.5°) to 107°. The most favourable arrangement is distorted tetrahedral i.e. pyramidal. In this, nitrogen atom lies at the centre and three hydrogen atoms occupying the triangular base and the orbital with a lone pair of electrons from the apex of the pyramid.

(ii) H₂O: In a water molecule, the central oxygen atom

has six electrons in the valence shell. Two of these electrons are mutually shared with the electrons of two hydrogen atoms to form two O - H bonds.

Hence, the central oxygen atom is H₂O is surrounded by two bond pairs and two lone pairs. These four electron pairs adopt tetrahedral arrangement. The presence of two lone pairs brings

distortion in the geometry of the molecule. The lone pairs repel the bond pairs more effectively resulting in the decrease of H – O – H angle from 109.5° to 104.5°. The water molecule may be regarded as bent or angular or V-shaped.