Q: 8. Ionic solids conduct electricity in molten state but not in solid state. Explain.
In ionic compounds, electricity is conducted by ions. In solid state, ions are held together by strong electrostatic forces and are not free to move about within the solid. Hence, ionic solids do not conduct electricity in solid state. However, in molten state or in solution form, the ions are free to move and can conduct electricity.
Q: 9. What is type of solids are electrical conductors, malleable and ductile?
Metallic solids are electrical conductors, malleable, and ductile.
Q: 10. Give the significance of a ‘lattice point’.
The significance of a lattice point is that each lattice point represents one constituent particle of a solid which may be an atom, a molecule (group of atom), or an ion.
Q: 11. Name the parameters that characterize a unit cell.
The six parameters that characterise a unit cell are as follows.
(I) Its dimensions along the three edges, a, b, and c
These edges may or may not be equal.
(II) Angles between the edges
These are the angle (between edges b and c), (between edges a and c), and (between edges a and b).
Q: 12. Distinguish between
(I) Hexagonal and monoclinic unit cells
(II) Face-centred and end-centred unit cells.
(I) Hexagonal unit cell
For a hexagonal unit cell,
Monoclinic unit cell
For a monoclinic cell,
(ii) Face-centred unit cell
In a face-centred unit cell, the constituent particles are present at the corners and one at the centre of each face.
End-centred unit cell
Anend-centred unit cell contains particles at the corners and one at the centre of any two opposite faces.