The Solid State

Question 217
CBSEENCH12005565

What makes alkali metal halides sometimes coloured, which are otherwise colourless?

Solution

Alkali metal halides have anionic sites occupied by unpaired electrons. These are called F-centres, and impart colour to the crystals of alkali metal halides. For example, the excess of lithium in LiCl makes it pink.

Question 218
CBSEENCH12005566

Define the term ‘amorphous’.

Solution
Amorphous solids are the solids whose constituent particles have a completely random arrangement. Amorphous solids do not have a sharp melting point and melt over a range of temperature. These solids are isotropic in nature. Amorphous solid have elasticity, electric conductance, reflective index and rate of dissociation are the same throughout all the direction. Amorphous solid always flow very slowly therefore, amorphous solids are sometimes called pseudo solids or super cooled liquids. Amorphous solid do not have definite heat of fusion. When we cut a piece of amorphous solid cut with a sharp–edged tool, they cut into two pieces with irregular surfaces. Examples :– glass, rubber, and plastic.
 
Question 219
CBSEENCH12005567

Which point defect lowers the density of a crystal?

Solution

Shottkey defect can lower the density of a crystal.

Question 220
CBSEENCH12005568

What is coordination number of a metal atom in ccp structure?

Solution

Coordination number of CCP is 12.

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