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Chemical Bonding and Molecular Structure

Long Answer Type

151.

Discuss the orbital shapes of the following covalent molecules:
(i) HF (ii) H₂O (iii) NH₃.

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Short Answer Type

152.
Why is a sigma bond stronger than pi bond ?

The strength of a bond depends on upon the extent of overlapping.
A sigma bond stronger than a pi bond. The reason behind this is the orientation of the overlapped orbitals. Sigma bonds result from head-on(co-axial) overlapping while pi bonds are the outcome of lateral(para-axial) overlapping. Here is a pictorial representation of ethene(sp² hybridised C atoms).

The greater the extent of overlapping, the higher the probability of finding the valence electrons in between the nuclei and hence the bond will be stronger.

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153.

Why are lone pair-lone pair repulsion stronger than lone pair-bond pair.

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Long Answer Type

154.

Describe, in brief, the types of covalent bonds ?

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155.

Using the orbital overlap concept, explain the formation of:
(i) O₂ molecule (ii) N₂ molecule.

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156.

Distinguish between a sigma $open parentheses straight sigma close parentheses$ bond and a $pi space left parenthesis straight pi right parenthesis$ bond.