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Chemistry Formula
The Solid State
1|Page
Chemistry Notes for class 12 Chapter 1 The
Solid State
Solids
Solids are the chemical substances which are characterised by define shape and volume,
rigidity, high density, low compressibility
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Distinction Between Crystalline and Amorphous Solids
S
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2
These are true solids
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These are anisotropic in nature, i
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, their physical
4
properties are different in different directions
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6
They undergo a clean cleavage when cut
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Theseare super cooled liquids or pseudo soilds
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These are isotropic in nature i
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, their physical
properties are same in all the directions
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They undergo irregular cleavage when cut
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If the waves are in phase after reflection, the difference in distance
travelled by the two rays ti
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, path difference) must be equal to an integral number of
Wavelength, nλ for constructive
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Where, n = 1
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Unit Cell
The smallest geometrical portion of the crystal lattice which can be used as repetitive unit to
build up the whole crystal is called unit cell
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(ii) Face centred unit cell In which the particles are present at the corners as well as at the
centre of each of six faces
(iii) Body centred unit cell In which the particles are present at the corners as well as at the
centre of the unit cell
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Number of Particles Per Unit Cell
Seven Crystal Systems
There are about 230 crystal forms, which have been grouped into 14 types of space lattices,
called Bravais Lattices, on the basis of their symmetry and seven different crystal systems on
the basis of interfacial angles and axes
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(i) Primitive cubic unit cell Atoms touch each other along edges
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524 or 52
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Hence, d = a / √2
or r = √2a / 4
Therefore; PF = 4 * 4 / 3 πr3 / (4r / √2)r3 = 0
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Hence, √3a / 2
or r = √3a / 4
Therefore; PF = 2 * 4 / 3 πr3 / (4r / √3)r3 = 0
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[In simple cubic lattice, CN is 6, in body centred lattice, CN is 8 and in face centred cubic
lattice, CN is 12]
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Close Packing in Crystals
Two Dimensional Packing of Constituent Particles
(i) Square close packing Space occupied by spheres is 52
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(ii) Hexagonal close packing Space occupied b