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 SiO₄^4- 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