Solid State

1.28 Coordination number is the number of the nearest neighbors with which a given atom is in contact. In an 
ionic crystal, the coordination number of an ion refers to the number of oppositely charged ions that 
surround that ion.
The coordination number of atoms in a
(a) Cubic close-packed structure is 12.
(b) Body-centred cubic structure is 8

1.27 The different solids are classified below:
a) Ionic solids: Ammonium phosphate (NH4)3PO4), LiBr
b) Metallic solid: Brass, Rb
c) Molecular solids: Tetraphosphorous decaoxide (P4O10), Iodine (I2), P4
d) Network (covalent) solids: Graphite, SiC, Si
e) Amorphous solid: Plastics

1.26 Quartzis crystalline solid with long range order and glass is amorphous solid (or pseudo solid or super cooled liquid) with short range order and has a tendency to flow. When quartzis heated, it can be converted into glass.

1.25 Amorphous solids have short-range order with irregular shapes of constituent particles. They have isotropic nature and melt over a range of temperatures. They do not have a definite enthalpy of fusion. Examples of amorphous solids are glass, rubber, plastic, etc.

1.24 Ferromagnetic substances would make better permanent magnets because when the ferromagnetic substance is placed in a magnetic field, all domains get oriented in the direction of magnetic field and strong a magnetic effect is produced.

1.23 An n-type semiconductor conducts because of the presence of extra electrons. Therefore, a group 14 element can be converted to n-type semiconductor by doping it with a group 15 element.

1.21 Two or more cations of lower valency are replaced by a cation of higher valency to maintain electrical neutrality. Hence some cation vacancies are created. For example : In an ionic solid 'NaCl', is impurity of Sr2+ is added (as SrCl2) then two Na+ ions left thus lattice sited. To maintain electrical neutrality one lattice site is occupied by Sr2+ ion while other lattice site will remain vacant.

1.20 ZnS shows Frenkel Defect.
AgBr shows Frenkel Defect and Schottky Defect. Frenkel Defect: It is a kind of defect in crystalline solids in which atoms are displaced from their lattice position 
to interstitial site creating vacancy at the lattice point. It usually occurs in ionic solid with large difference in size 
of ions.
Schottky Defect: This defect occurs when oppositely charged ions leave their lattice site creating vacancies in 
such a way that electrical neutrality of crystal is maintained. It is generally seen in highly ionic compounds where 
difference in size of cation and anion is small.

1.19 When a solid is heated, vacancy defect can arise. A solid crystal is said to have vacancy defect when some of the lattice sites are vacant. Vacancydefect leads to a decrease in the density of the solid.