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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.

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Long Answer Type

168.
On the basis of VSEPR theory, discuss the geometry of the following covalent molecules: (i) BeF₂(ii) BF₃(iii) CH₄.

(i) BeF₂ : The electronic configuration of Be (Z = 4) is1s²2s². The central atom Be has 2 valence electrons. These two electrons are shared mutually with the electrons of two fluorine atoms to form two Be – F bonds.

To have a minimum repulsion in the electron pairs around the central atom, the geometry of the molecules is regular as well as linear. Bond angle in such cases is 180°.

(iii) BF₃: The electronic configuration of B (Z = 5) is 1s² 2s² 2p¹_x. The central atom B has 3 valence electrons. These three valence electrons are shared mutually with the electrons of the fluorine atoms to form three B - F bonds.

Thus, B atom is surrounded by three bond pairs. These repel each other and go as far apart as possible so that there are no further repulsions. This is so if the three electron pairs are placed at 120° with respect to each other i.e. the most favourable arrangement is the triangular planar geometry.

(iii) CH₄ The electronic configuration of C(Z =6) is

The central atom has 4 valence electrons. These four valence electrons are shared mutually with the electrons of four hydrogen atoms to form four C - H bonds as shown.

Thus carbon atom is surrounded by four bond pairs. In order to minimise the inter-electron pair repulsions i.e. having a state of minimum enthalpy and hence maximum stability, these bond pairs should be as far apart from one another as possible. This is so if the four electron pairs are placed at an angle of 109.5° with respect to each other i.e. the most favourable arrangement is tetrahedral geometry. In other words, carbon is present in the centre of a regular tetrahedron and four bond pairs are directed to the four corners with bond angle-critical to 109.5°.