Q.1 which out of NaCl and CsCl, has larger coordination number?
Ans. Coordination number of Cscl=8;
Coordination number of Nacl=6
∴ CsCl has larger coordination number.
Q.2 Name one solid which shows both Frenkel and Schotty defects.
Ans. AgBr shows both, Frenkel as well as Schottky defects.
Q.3 What happens to the structure of CsCl when it is heated to about &60 K?
Ans. CsCl structure is transformed to NaCl structure.
Q.4 Arrange simple cubic,body centred cubic,face-centred cubic and hexagonal close packing in the increasing order of the fraction of occupied space.
Ans. Simple cubic <bcc<fcc
Q.5 What is the effect of Schottky defects on the density of the crystal.
Ans.The overall density of the crystal decreases in Schottky defects.
Q.6 Why is frenkel defect not found in pure metal halides?
Ans. Because in metal(alkali) halides,ions cannot get into interstitial sites due to their larger sizes.
Q.7 In a close packing of N spheres,how many(i) tetrahedral and (ii) Octahedral sites are present?
Ans. Tetrahedral=2N (ii) Octahedral=N
Q.8 What is photovoltaic cell?
Ans. Amorphous silicon acts as a typical photovoltaic cell in which as a result of sunshine(sunlight) electricity is produced.
Q.9 How does temperature influence the conductivity of a cell?
Ans. Its conductivity increase with increase in temperature.
Q.10 What is the difference in semi-conductor obtained by doping silicon with As or with Ga?
Ans. Si produced by doping with As in n-type semi-conductor in which flow of current is due to electrons while silicon doped with Ga is p-type semi-conductor in which flow of current is due to positive holes.
Q.11 Give three examples of amorphous solids.
Ans. Glass,rubber and plastics.
Q.12 what is Schottky defects?
Ans. When equal number of cations and anions are missing from their lattice sites.
Q.13 What are interstitials in a crystals?
Ans. Atoms or ions that fill the normal vacant interstitial voids in a crystal are called interstitials.
Q.14 What is the effect of presence of frenkel defects on the density of a crystal?
Ans. The density of the crystal does not change.
Q.15 How many atoms are present in the unit cell of (a) Simple cubic lattice,(b) BCC,(C)FCC?
Ans. (a) Number of atoms in the simple cubic lattice=1
(b) Number of atoms in the BCC=1
(c) Number of atoms in the FCC=1
Q.16 How can you convert NaCl structure into CsCl structure and vice-versa?
Ans. NaCl structure can be converted into CsCl structure by application of pressure,while reverse can be done by heating CsCl to 760K.
Q.17 What is coordination number of Naᐩ and Cl⁻ ions in NaCl structure?
Ans. Six.
Q.18 At what temperature ferrrimagnetic substance changes to paramagnetic?
Ans. 850 K
Q.19 In a crystal of Zns,Zinc occupies tetrahedral voids.What is the coordination number of Zinc?
Ans. 4
Q.20 What is meant by supercomductivity?
Ans. At low temperature when a substance offers no resistance to the flow of electricity,the phenomenon is known as superconductivity.
Q.21 What is energy gap in band theory ? Compare its size in conductors,semi-conductor and insulators?
Ans. Energy gap in band theory means the gap energy between valence band conduction band. The gap is in order conductor < semi-conductor<insulator.
Q.22 what is F-centre?
Ans. The site where electron is entrapped in anion vacancy is called F-centre.
Q.23 What is the maximum possible coordination number of an atom in an hcp crystal structure of an element?
Ans. 12
Q.24 What happens when ferrimagnetic Fe3O4 is heated to 850 K and why?
Ans. Ferrimagnetic Fe3O4 on heating to 850 K becomes paramagnetic.This is due to grteater aligment of spins in one direction on heating.
Q.25 In CaF2 crystal,Ca^+2 ions are present in fcc arangement.Calculate the number of F^- ions in the unit cell.
Ans. No. of Ca^2+ ions per unit cell=8 × 1/8 + 6 ×1/2 =4
Hence,No. of F^- ions per unit cell=2 ×4=8
Q.26 What is the coordination number of an octahedral voids?
Ans. Six
Q.27 What type of crystal defect is produced when Nacl is doped with MgCl2 ?
Ans. It is called impurity defect.A cation vacancy is produced.A substitutional solid solution is formed(because 2Na^+ ions are replaced by one Mg^+2 ions in the lattice).
Q.28 Mention one property which is caused due to the presence of F-centre in a solid.
Ans. F-centre is reponsible for the colour and paramagnetic behavior.
Q.29 At what temperature range most of the metals became super conductors?
Ans. 2k - 5K.
Q.30 How can a material be made amorphous ?
Ans. By melting the material and then cooling it suddenly.
