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The Solid State

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Chemistry I

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Class 10 Class 12
An element X with an atomic mass of 60 g/mol has density of 6.23 g/cm–3. If the edge length of its cubic unit cell is 400 pm, identify the type of cubic unit cell. Calculate the radius of an atom of this element.

we have given that 
Density, d = 6.23 g/cm3
              a = 400 pm
              M = 60g/mol-1
Volume  = (a3)=(400)3 = (400×10-10 cm)3


NAM=6.023×1023 mol-160 g/mol 

Z = 6.023 g cm-3×(400)3×10-30 cm3×6.023×1023 mol-160 g mol-1    = 6.023×64×6.023600   = 2401.49600=4.

Hence, the type of cubic unit cell is FCC

Radius = aa2=40022=2002

              = 2001.414=141.4 pm. 

So radius of element is 141.4 pm


Why are solids rigid?

Solids are rigid because the internuclear distance between the  molecules of a solid are very less and closely packed and their positions are fixed due to the strong forces of attraction between them.

Why is glass considred a super-cooled liquid?

Glass is amorphous solids and  have a tendency to flow, though very slowly. Therefore, these are called pseudo solids or super cooled liquids .

Classify the following as amorphous or crystalline solids: Polyurethane, naphthalene, benzoic acid, teflon, potassium nitrate, cellophane, polyvinyl chloride, fibre glass, copper.

Amorphous solids: Polyurethane, teflon, cellophane, polyvinyal chloride, fibre glass.
Crystalline solids: naphthlene, benzoic acid, potassium nitrate, copper.

Refractive index of a solid is observed to have the same value along all directions. Comment on the nature of this solid. Would it show clevage property?

Refractive index of a solid which have the same value along all directions are isotropic in nature. It would not show cleavage property.

Why do solids have a definite volume?

A solid have a definite volume because the inter molecular distance  between its molecules are fixed.