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The Solid State

Short Answer Type

121. Give reasons for Non-stoichiometric sodium chloride is a yellow solid.

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Long Answer Type

122. What is a semi-conductor? Describe the two main types of semi-conductors and contrast their conduction mechanism.

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123. A cubic solid is made of two elements P and Q. Atoms of Q are at the corners of the cube and P at the body centre. What is the formula of the compound? What are the coordination numbers of P and Q?

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Short Answer Type

124. What is the difference between Schottky defects and Frenkel defects?

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Long Answer Type

125. If the radius of the octahedral void is r and radius of the atoms in close packing is R, derive relation between r and R.

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Short Answer Type

126. Pure silicon is an insulator. Silicon doped with phosphorus is a semi-conductor. Silicon doped with gallium is also a semiconductor. What is the difference between the two doped silicon semi-conductor?

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Long Answer Type

127. What are paramagnetic and ferromagnetic substances. Account for the paramagnetic character of transition metal compounds. How does the paramagnetic character of the bivalent ions of the first transition metal series varies from Ti (Z = 22) to Cu (Z = 29)?

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128. Non-stoichiometric cuprous oxide, Cu₂O can be prepared in laboratory. In this oxide, copper to oxygen ratio is slightly less than 2 :1. Can you account for the fact that this substance is a p-type semi-conductor ?

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Short Answer Type

129. Ferric oxide crystallizes in a hexagonal close packed array of oxide ions with two out of every three tetrahedral holes occupied by ferric ions. Derive the formula of the ferric oxide.

Let us Suppose the number of oxide (O^2–) ions = N.
Number of octahedral void = number of anions
So that the number of octahedral voids = N

We have Given that

Two out of every three octahedral holes are occupied by ferric ions.

So that the number of ferric (Fe³⁺) ions = 2N/3
The ratio of the number of Fe3+ ions to the number of O²⁻ ions,

Fe3+ : O²⁻ = 2N/3 : N

Multiply 3 and divide by N we get

Fe3+ : O2− = 2 : 3

Hence, the formula of the ferric oxide is Fe₂O₃.

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Long Answer Type

130. Classify each of the following as being either a p-type or an n-type semi conducor:
(i) Ge doped with In
(ii) B doped with Si.

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