Q.1.
In a close packing of N spheres, how many (i) tetrahedral, and (ii)
octahedral sites are present?
Q.2. What is the relationship between the edge length ‘a’ of the unit cell and radius ‘r’ of an atom in a face centred unit cell?
Q.3. A metal crystallizes in a body centred cubic structure. If ‘a’ is the edge length of its unit cell, ‘r’ is the radius of the sphere. What is the relationship between ‘r’ and ‘a’?
Q.4. What type of solids are electrical conductors, malleable and ductile?
Q.5. If the radius of the octahedral void is ‘r’ and radius of the atoms in close packing is ‘R’. What is the relation between ‘r’ and ‘R’?
Q.6. Arrange simple cubic, body centred cubic, face centred cubic and hexagonal close packing in the increasing order of packing efficiency.
Q.7. (a) What is meant by the term coordination number?
(b) What is the coordination number of atoms:
(i) in a cubic close packed structure
(ii) in a body centred cubic structure?
Q.8. The ions of NaF and MgO all have the same number of electrons and the internuclear distances are about the same (235 pm and 215 pm).Why then are the melting points of NaF and MgO so different (992 °C and 2642 °C)?
Q.9. Name the (i) most symmetrical and (ii) most unsymmetrical crystal system.
Q.10. How many atoms can be assigned to its unit cell if an element forms (i) a body centred cubic cell and (ii) face centred cubic cell?
Q.11. What is the maximum coordination number of an atom in a hcp crystal structure of an element.?
Q.12. Which network solid is an exceptionally good conductor of electricity?
Q.13. How are unit cell and space lattice related?
Q.14. Pick out the odd ones from the following sets:
(i) Sulphur, Argon, Solid CO2, Diamond
(ii) SiC, Quartz, BaO, Graphite
Q.15. An iron oxide crystallizes in a hexagonal close packed arrangement of oxide ions with two out of every three octahedral voids occupied by iron. Give the formula of the iron oxide.
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