Vidaara.orgClass 10 · Chemistry
CodeVID-C10-04-T1-01
Assignment — Covalent Bonding & Allotropes of Carbon
Name: ____________________
Roll No.: __________
Date: ____________
General Instructions
- All questions are compulsory.
- Section A carries 1 mark each, Section B 2 marks, Section C 3 marks and Section D 5 marks.
- Show all working for Sections B, C and D. Only final answers are given at the end — for full solutions, raise your doubts with your teacher.
Section A — Multiple Choice Questions
5 × 1 = 5 marks
1.
The valency of carbon is:
- A.2
- B.3
- C.4
- D.6
2.
The number of shared electron pairs in a double bond is:
- A.1
- B.2
- C.3
- D.4
3.
The hardest natural allotrope of carbon is:
- A.graphite
- B.fullerene
- C.diamond
- D.coke
4.
Buckminsterfullerene has the formula:
- A.C12
- B.C60
- C.C6
- D.C100
5.
Covalent compounds are generally:
- A.good conductors of electricity
- B.poor conductors of electricity
- C.always soluble in water
- D.high-melting solids
Section B — Short Answer (2 marks)
3 × 2 = 6 marks
6.
Define a covalent bond and give one example.
7.
What is meant by the tetravalency of carbon?
8.
State two physical properties of covalent compounds.
Section C — Short Answer (3 marks)
2 × 3 = 6 marks
9.
Explain why carbon forms a very large number of compounds.
10.
Compare diamond and graphite with respect to structure and electrical conductivity.
Section D — Long Answer (5 marks)
1 × 5 = 5 marks
11.
Explain how carbon achieves a stable octet, describe single, double and triple bonds with one example each, and define allotropy naming three allotropes of carbon.
Answer Key
Section A — Multiple Choice Questions
- (C) 4
- (B) 2
- (C) diamond
- (B) C60
- (B) poor conductors of electricity
Section B — Short Answer (2 marks)
- A covalent bond is formed by the sharing of a pair of electrons between two atoms, e.g. the C-H bond in methane (CH4).
- Carbon has 4 valence electrons and needs 4 more for an octet, so it forms 4 covalent bonds; this four-bond nature is called tetravalency.
- They have low melting and boiling points and are poor conductors of electricity (they have no free ions or electrons).
Section C — Short Answer (3 marks)
- Carbon shows tetravalency (forms 4 bonds) and strong catenation (links with other carbon atoms forming long chains, branches and rings). The C-C bond is strong and stable, so chains of almost any length are possible, giving millions of compounds.
- In diamond each carbon is bonded to four others in a rigid 3-D network with no free electrons, so it does not conduct. In graphite each carbon is bonded to three others in layers and the fourth electron is free, so graphite conducts electricity and is soft.
Section D — Long Answer (5 marks)
- Carbon (2, 4) cannot easily gain or lose 4 electrons, so it shares 4 electron pairs (covalent bonding) to complete its octet. A single bond shares 1 pair (C-C in ethane C2H6), a double bond shares 2 pairs (C=C in ethene C2H4) and a triple bond shares 3 pairs (C-C triple in ethyne C2H2). Allotropy is the existence of an element in different physical forms with different properties; three allotropes of carbon are diamond (rigid 3-D network, hardest), graphite (layered, soft, conducts electricity) and fullerene (cage-like, e.g. C60).
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