Class 11 Chemistry Ch-11 The p-Block Elements (VSQ)

Q.1. Name the element of group 13 which forms only covalent compounds.

Answer Answer: B forms only covalent compounds.

Q.2. Explain why silicon shows a higher covalency than carbon?

Answer Answer: Si because of the presence of vacant d–orbitals can show a covalency upto six while C because of the absence of d– orbitals cannot have a covalency of more than four.

Q.3. Why is diamond a bad conductor of electricity but a good conductor of heat?

Answer Answer: In diamond all the valence electrons are involved in forming carbon-carbon bonds and does not have free electrons and, therefore, it is a bad conductor of electricity. Conduction of heat does not necessarily require movement of electrons thus diamond is a conductor of heat.

Q.4. Which oxide of carbon is an anhydride of carbonic acid ?

Answer Answer: CO2 is an anhydride of carbonic acid: H2CO3 → H2O + CO2.

Q.5. What are boranes?

Answer Answer: Refer Textbook

Q.6. Why boron forms electron deficient compounds?

Answer Answer: Boron has three electrons in the outermost shell which it can share with other atoms. Hence, in its compounds, only 6 electrons are present around B–atom, i.e., octet is not complete. Thus boron forms electron deficient compounds.

Q.7. Why boron halides do not exist as dimer while AlCl3 exists as Al2Cl6 ?

Answer Answer: Boron atom being small in size is unable to accommodate four large sized halogen atoms around it to form dimer. Thus BCl3 exists as a monomer whereas AlCl3 exists as a dimer Al2Cl6.

Q.8. Why B–X bond distance in BX3 is shorter than theoretically expected value?

Answer Answer: This is due to pπ – pπ back bonding of the fully filled p– orbital of halogen (X) atom with the empty p–orbital of boron atom.

Q.9. The +1 oxidation state is more stable than the + 3 oxidation state for thallium.

Answer Answer: Refer Textbook

Q.10. Why carbon forms covalent compounds whereas lead forms ionic compounds?

Answer Answer: Refer Textbook

Q.11. Why is boron used in nuclear reactors?

Answer Answer: Boron can absorb neutrons.

Q.12. Why does boron resemble Si?

Answer Answer: Both have similar charge over radius ratio, i.e., similar polarising power.

Q.13. What name is given to the compounds formed by more electropositive elements with carbon?

Answer Answer: Ionic compounds.

Q.14. Is carbon dioxide poisonous or not?

Answer Answer: No, it is not poisonous.

Q.15. Between AlF3 and AlCl3 which one will have a higher melting point.

Answer Answer: AlF3 is more ionic, therefore, has higher melting point.

Q.16. How are linear silicones obtained?

Answer Answer: Refer Textbook

Q.17. Graphite is used as solid lubricant but charcoal is not, why?

Answer Answer: Graphite is soft due to which it can be used as solid lubricant whereas charcoal is hard due to which it cannot be used as lubricant.

Q.18. What are silicates?

Answer Answer: Silicates are minerals which consist of SiO44- units arranged in different ways.

Q.19. BCl3 exists but BH3 does not. Explain.

Answer Answer: In BCl3, Cl donates lone pair of electrons to vacant p-orbital of boron (back-bonding) making it more stable whereas in BH3 back-bonding is not possible, therefore, it exists as dimer. Secondly, in BCl3, chlorine being bigger in size cannot form bridged bonds.

Q.20. Silanes gets hydrolysed by water whereas alkanes do not, why?

Answer Answer: Silane gets hydrolysed because silicon has vacant d-orbital whereas alkane cannot due to non-availability of vacant dorbital in carbon.

Q.21. Explain the following statement with reason.
The fullerene is considered as purest allotrope of carbon.

Answer Answer: It is because it does not have edges, therefore, impurities cannot be adsorbed on it.

Q.22. Explain why boron halides don’t conduct electricity in the liquid state?

Answer Answer: Boron halides don’t conduct electricity in the liquid state because they are covalent compounds.

Q.23. What is the use of boron nitride?

Answer Answer: Boron nitride is harder than diamond and is used as an abrassive.

Q.24. Give one example each of ionic and covalent carbides.

Answer Answer: CaC2 is ionic carbide while SiC is the covalent carbide.

Q.25. (CH3)3N is basic but (CF3)3N is not basic. Explain.

Answer Answer: This is due to different electronegativities of H and F bonded to nitrogen. In (CH3)3 N, the lone pair on N is concentrated on N and so it can act as an electron pair donor (Lewis base). However in (CF3)2 N, the electron density on N is decreased due to strongly electronegative F atom attached to C. Hence, it cannot act as a Lewis base

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