Case study (4 Marks)

Question 14 Marks

When anions and cations approach each other, the valence shell of anions are pulled towards the cation nucleus and thus, the shape of the anion is deformed. The phenomenon of deformation of anion by a cation is known as polarization and the ability of the cation to polarize the anion is called as polarizing power of cation. Due to polarization, sharing of electrons occurs between two ions to some extent and the bond shows some covalent character.
The magnitude of polarization depends upon a number of factors.

1. Out of $AlCl _3$ and $AlI _3$ which halides show maximum polarization?
2. Out of $AlCl _3$ and $CaCl _2$ which one is more covalent in nature?
3. The non-aqueous solvent like ether is added to the mixture of $LiCl , NaCl$ and KCl . Which will be extracted into the ether?
OR
Out of $CaF _2$ and $CaI _2$ which one has a minimum melting point?

Answer

1. $AlI _3$ halides show maximum polarization. The most covalent halide is $AlI _3$.
Since lesser, the electronegativity difference, the more covalent is the aluminum halide.
2. $AlCl _3$ is more covalent in nature.
3. LiCl will be extracted into the ether.
OR
$CaI _2$ has a minimum melting point.

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Question 24 Marks

The phenomenon of the existence of two or more compounds possessing the same molecular formula but different properties is known as isomerism. Such compounds are called isomers. Compounds having the same molecular formula but different structures (manners in which atoms are linked) are classified as structural isomers. Structural isomers are classified as chain isomer, position isomer, functional group isomer. Meristematic arises due to different alkyl chains on either side of the functional group in the molecule and stereoisomerism and can be classified as geometrical and optical isomerism. Hyperconjugation is a general stabilising interaction. It involves delocalisation of $\sigma$ electrons of the C-H bond of an alkyl group directly attached to an atom of an unsaturated system or to an atom with an unshared p orbital. This type of overlap stabilises the carbocation because electron density from the adjacent $\sigma$ bond helps in dispersing the positive charge.

1. Why Isopentane, pentane and Neopentane are chain isomers?
OR
Why hyperconjugation is a permanent effect?
2. The molecular formula $C _3 H _8 O$ represents which isomer?
3. What type of isomerism is shown by Methoxypropane and ethoxyethane?

Answer

1. Isopentane, pentane and Neopentane are chain isomers because they have a similar molecular formula but a different carbon skeleton.
OR
The $\sigma$ electrons of C-H bond of the alkyl group enter into partial conjugation with the attached unsaturated system or with the unshared p orbital therefore hyperconjugation is permanent effect.
2. The molecular formula $C _3 H _8 O$ represents positional isomers because they differ in the position of substituent functional group $( OH )$ on the carbon skeleton.
3. Methoxypropane and ethoxyethane are metamers because none of its side are similar to each other.

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Chemistry Case study (4 Marks)

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