The Solid State

Question 217

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


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

Define the term ‘amorphous’.

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

Which point defect lowers the density of a crystal?


Shottkey defect can lower the density of a crystal.

Question 220

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


Coordination number of CCP is 12.

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