Question

Give reasons for the following:
(I) Covalent compounds are poor conductor of electricity.
(II) Soap does not form lather in hard water.
(III) Carbon shows catenation but silicon does not.

Hint:

(I) Covalent compounds: no free electrons/ions \(\Rightarrow\) no conductivity. (II) Hard water: Ca²⁺/Mg²⁺ react with soap \(\Rightarrow\) insoluble scum \(\Rightarrow\) no lather. (III) Catenation: C-C strong (small size); Si-Si weak (large size).

Answer 1

Part (I): Covalent compounds are poor conductors of electricity

Step 1: Requirement for electrical conduction.
A substance can conduct electricity only if it contains free moving charged particles such as ions or free electrons.

Step 2: Structure of covalent compounds.
Covalent compounds are formed by sharing of electrons between atoms.
They exist as neutral molecules and not as ions.

Step 3: Lack of free charge carriers.
In covalent compounds, the shared electrons are localized between atoms and are not free to move.
They do not ionize in molten or solid state.
Since there are no free ions or electrons, electric current cannot pass through them.

Step 4: Conclusion.
Hence, covalent compounds are generally poor conductors of electricity because they do not have free ions or delocalized electrons to carry charge.

Part (II): Soap does not form lather in hard water

Step 1: Nature of soap and hard water.
Soap is the sodium or potassium salt of long chain fatty acids.
Hard water contains calcium (Ca²⁺) and magnesium (Mg²⁺) ions.

Step 2: Reaction between soap and hardness ions.
When soap is added to hard water, Ca²⁺ and Mg²⁺ ions react with soap to form insoluble salts called scum.
2C₁₇H₃₅COONa + Ca²⁺ → (C₁₇H₃₅COO)₂Ca ↓ + 2Na⁺

Step 3: Effect on lather formation.
The insoluble scum precipitates out and consumes the soap.
Since soap is used up in forming scum, sufficient lather is not produced.

Step 4: Conclusion.
Soap does not form lather in hard water because calcium and magnesium ions form insoluble precipitates with soap, preventing lather formation.

Part (III): Carbon shows catenation but silicon does not

Step 1: Meaning of catenation.
Catenation is the property of an element to form long chains or rings by bonding with atoms of the same element.

Step 2: Reason for carbon’s catenation.
Carbon has a small atomic size which allows strong C–C bond formation.
The C–C bond energy is high, making the chains stable.
Carbon is tetravalent and can form single, double and triple bonds.
These factors allow formation of long chains and complex structures.

Step 3: Why silicon shows very little catenation.
Silicon atoms are larger in size, leading to weaker Si–Si bonds.
The bond energy of Si–Si is much lower than C–C.
Silicon prefers forming strong Si–O bonds rather than long Si–Si chains.

Step 4: Conclusion.
Carbon shows extensive catenation due to strong C–C bonds and small atomic size, whereas silicon shows very limited catenation because Si–Si bonds are weaker and less stable.