Briefly explain the packing of the constituent particles in a crystal.

Why is glass regarded as an amorphous solid?

Classify each of the following solids as molecular, ionic, network (covalent), metallic or amorphous:

(i) ${\mathrm{I}}_2$     (ii) Tetraphosphorus decaoxide (${\mathrm{P}}_4{\mathrm{O}}_{10}$)     (iii) ${\mathrm{P}}_4$     (iv) ${\mathrm{S}}_8$    (v) Plastic

(vi) Brass   (vii) $\mathrm{SiC}$  (viii) Graphite  (ix) $\mathrm{Rb}$    (x) $\mathrm{Si}$   (xi) Ammonium phosphate

(xii) $\mathrm{LiBr}$    (xiii) Wax    (xiv) Ice     (xv) Solid ${\mathrm{CO}}_2$       (xvi) $\mathrm{Al}$      (xvii) Naphthalene

(xviii) $\mathrm{CsCl}$      (xix) Sugar      (xx) ${\mathrm{SiO}}_2$      (xxi) Glass

Why the window glass panes of the old buildings are thick at the bottom?

Some glass objects from ancient civilisations look milky instead of being transparent. Explain.

Show that the density of a cubic crystal is given by the expression:

$\mathrm{d}=\frac{\mathrm{ZM}}{{\mathrm{a}}^3{ \mathrm{N}}_{\mathrm{A}}}$

where $\mathrm{Z}$ is the number of atoms/molecules/ions present per unit cell, $\mathrm{M}$ is molecular weight, ${\mathrm{N}}_{\mathrm{A}}$ is Avogadro's number and ${\mathrm{a}}^3$ is the volume of unit cell.