CBSE Class 12-science Answered

14. What is the difference between primitive and centered unit cell? 15. Calculate the number of atoms in a) SCC b) BCC c) FCC unit cells. 16. Mention the characteristics of seven primitive unit cells and their possible variation as centered unit cells. 17. Name the centered unit cells and position of atoms in each centered unit cell. 18. What do you mean by coordination number? Give the coordination number of atoms in a) one dimensional arrangement of atoms b) square close packing in two dimension. c) hexagonal close packing in two dimension c) hexagonal close packing in three dimension d) cubic close packing or fcc in three dimension e) cation in triangular void. f) cation in tetrahedral void g) cation in cubic void h) bcc 19. A compound has hexagonal close packing structure. Determine the total number of voids, number of tetrahedral void, and number of octahedral voids in 0.5 mole of this compounds. 20. Calculate the number of octahedral and tetrahedral voids in unit cells of a)SCC b)BCC c)FCC 21. Distinguish between a) octahedral and tetrahedral voids b) Schottky and Frenkel defect. c) Hexagonal closed packing and cubic close packing d) crystal lattice and unit cell. e) para magnetism and ferro magnetism f) hexagonal and monoclinic unit cell g) face centered and end centered unit cell. 22. Calculate the % efficiency of packing in a) SCC b) BCC c) FCC 23. If the radius of octahedral void is r and the radius of atoms in close packing is R, derive the relationship between r and R. 24. What are interstitial defects? Mention its effect on density of a solid. 25. What is the effect of adding a) SrCl2 to NaCl b) CdCl2 to AgCl? 26. Explain the terms with suitable examples a) Stoichiometric and non stoichiometric defects b) F centre c) Metal deficiency defect d) 12-16 and 13-15 compounds e) paramagnetism f) diamagnetism g) ferromagnetism h) ferrimagnetism i) antiferromagnetism 27. What happens when a) NaCl crystal is heated with Na vapors b) ZnO is heated c) Fe3O4 is heated. 28. Explain n type and p type conduction with suitable examples. 29. Classify the following as n type or p type semi conductors. a) Ge doped with In b) B doped with Si. 30. In terms of band theory explain the differences between conductor , insulator, and semi conductor. Draw a neat diagram to show the valence band and conduction band in conductor, insulator and semi conductor. 31. Derive the expression for determining the density of unit cell.

Asked by Shubham Goyal | 09 Mar, 2013, 07:03: AM

Expert Answer

Request you to ask one question at a time. It is very difficult to read and answer.

When a unit in a crystal lattice has lattice points only at its corners ,it is called a simple or primitive unit cell. There are seven types of primitive unit cells among crystal.They are
1. Cubic unit cell
2. Tetragonal unit cell
3. Orthorhombic unit cell
4. Monoclinic unit cell
5. Rhombohedral unit cell
6. Triclinic unit cell
7. Hexagonal unit cell

And, the smallest repeating unit in space lattice which when repeated over and over again produces the complete space lattice.This is called unit cell.

In easy form , The unit cell which do not contain any interior point are called primitive unit cell.

Answered by | 09 Mar, 2013, 10:56: AM