Vidaara.orgClass 12 · Chemistry
CodeVID-C12-01-CH-01
Chapter Assignment — The Solid State
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.
- Use $N_A=6.022\times10^{23}$ where required and show all working for Sections B, C and D.
- Only final answers are provided — for full solutions, raise your doubts with your teacher.
Section A (1 mark each)
6 × 1 = 6 marks
1.
Which solid is isotropic?
- A.Quartz
- B.Glass
- C.Diamond
- D.NaCl
2.
Number of atoms in an fcc unit cell:
- A.1
- B.2
- C.4
- D.8
3.
Packing efficiency of hcp:
- A.52.4%
- B.68%
- C.74%
- D.100%
4.
Schottky defect changes density by:
- A.increasing it
- B.decreasing it
- C.no change
- D.tripling it
5.
p-type semiconductors carry current via:
- A.extra electrons
- B.positive holes
- C.protons
- D.neutrons
6.
$\text{Fe}_3\text{O}_4$ is:
- A.diamagnetic
- B.paramagnetic
- C.ferrimagnetic
- D.antiferromagnetic
Section B (2 marks)
4 × 2 = 8 marks
7.
Give two differences between crystalline and amorphous solids.
8.
State the edge–radius relation and packing efficiency for an fcc lattice.
9.
Distinguish the Schottky and Frenkel defects by their effect on density.
10.
How many tetrahedral and octahedral voids occur for $N$ close-packed spheres?
Section C (3 marks)
2 × 3 = 6 marks
11.
An element crystallises in bcc with $M=23\ \text{g/mol}$ and $a=4.29\times10^{-8}\ \text{cm}$. Find its density.
12.
Explain n-type and p-type semiconductors with one dopant example each.
Section D (5 marks)
2 × 5 = 10 marks
13.
Derive the packing efficiency of a bcc lattice (68%) starting from the body-diagonal relation, and state $z$ and the coordination number.
14.
Classify point defects (stoichiometric and non-stoichiometric) and explain Schottky, Frenkel, metal-excess and impurity defects with examples.
Answer Key
Section A (1 mark each)
- (B) Glass
- (C) 4
- (C) 74%
- (B) decreasing it
- (B) positive holes
- (C) ferrimagnetic
Section B (2 marks)
- Crystalline: long-range order, sharp melting point, anisotropic. Amorphous: short-range order, softens over a range, isotropic.
- $\sqrt{2}\,a=4r$; packing efficiency $=74\%$.
- Schottky decreases density (ions removed); Frenkel keeps it unchanged (ion shifted to an interstitial site).
- Tetrahedral $=2N$; octahedral $=N$.
Section C (3 marks)
- $d=\frac{2\times23}{(4.29\times10^{-8})^3\times6.022\times10^{23}}\approx0.97\ \text{g cm}^{-3}$ (sodium).
- n-type: Si doped with P (Group 15) supplies a free electron. p-type: Si doped with B (Group 13) creates a positive hole.
Section D (5 marks)
- For bcc, $z=2$, coordination number $=8$, and $\sqrt{3}\,a=4r$ so $r=\frac{\sqrt{3}}{4}a$. Efficiency $=\frac{2\times\frac{4}{3}\pi r^3}{a^3}=\frac{\sqrt{3}\pi}{8}=0.68=68\%$.
- Stoichiometric: Schottky (equal cation/anion vacancies, density falls, NaCl) and Frenkel (ion in interstitial site, density unchanged, ZnS). Non-stoichiometric: metal excess (anion vacancy + trapped electron = F-centre, colour) and metal deficiency ($\text{Fe}_{0.95}\text{O}$). Impurity: $\text{Sr}^{2+}$ in NaCl replaces two $\text{Na}^+$, creating a cation vacancy.
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