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The Solid State

Short Answer Type

101. Why is potassium chloride sometimes violet instead of pure white.

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102. What is the coordination number of each type of ions in a rock-salt type crystal structure?

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103. What is the total number of atoms per unit cell in a face-centred cubic (fcc) structure?

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104. What type of substances exhibits anti-ferromagnetism?

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105. Define the term ‘amorphous’. Give a few examples of amorphous solids.

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106. What makes a glass different from a solid such as quartz? Under what conditions could quartz be converted into glass?

It is the arrangement of constituent particles of glass which makes it different from quartz. The constituent particles of glass have short range order while quartz has constituent particles in long range order and short range order both.

By heating and cooling rapidly quartz can be converted into glass.

Property

Quartz

Glass

1. Structure

2. Melting point

Quartz is crystalline and it has long range order.

Quartz has a sharp melting point. It changes into viscous liquid at 1983 K.

Amorphous silica does not have a regular structure of long range order.

Glass does not have a sharp melting point. On heating it softens and melts over a wide range of temperature.

If SiO₂ is melted and the melt is cooled very, rapidly it forms a glass.

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

(i) Tetra phosphorous decoxide (P₄O₁₀)

(ii) Ammonium phosphate (NH₄)₃PO₄

(iii) SiC

(iv) I₂

(v) P₄

(vi) Plastic

(vii) Graphite

(viii) Brass

(ix) Rb

(x) LiBr

(xi) Si

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108. What is meant by the term ‘coordination number’?

(ii) What is the coordination number of atoms:

(a) in a cubic close-packed structure?

(b) in a body-centred cubic structure?

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109. What is the co-ordination number of atoms:
(i) in a cubic close packed structure?
(ii) in a body centred cubic structure?

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Long Answer Type

110. How can you determine the atomic mass of an unknown metal if you know its density and the dimension of its unit cell? Explain.

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