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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
...
Distinction Between Crystalline and Amorphous Solids
S
...
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
...
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 by spheres is 60
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Hence
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Three Dimensional Packing of Constituent Particles
(i) ABAB arrangement gives hexagonal close packing (hcp)
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In both these arrangements 740/0 space is occupied
Coordination number in hop and ccp arrangement is 12 while in bcc arrangement, it is 8
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All noble gases have ccp structure except He (hcp structure)
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When particles are closed packed resulting in either cpp or hcp
structure, two types of voids are generated:
Tetrahedral voids are holes or voids surrounded by four spheres Present at the corner of
a tetrahedron
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Octahedral voids are holes surrounded by six spheres located on a regular tetrahedron
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[The number of octahedral voids present in a lattice is equal to the number of close packed
particles
...
]
Density of Unit Cell (d)
Density of unit ce11 = mass of unit cell / volume of unit cell
d = Z * M / a3 = ZM / a3 * NA
(The density of the unit cell is same as the density of the substance
...
of atoms per unit cell
NA = Avogadro number
a = edge length of unit cell
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Radius Ratio and Crystal Structure
Ionic crystals may be of two types
(i)AB type and
(ii) A2B or AB2
Structure of Ionic Crystals
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On applying pressure NaC} structure (6 : 6 coordination) changes into CsCI structure (8 : 8
coordination) and reverse of this occur at high temperature (760 K)
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derivations from perfect arrangement
may occur due to rapid cooling or presence of additional particles
...
Point Defects
Point defects are the irregularities or deviations from ideal arrangement around a point or an
atom in a crystalline substance Point defects can be classified into three types : (1)
psychometric defects (2) impurity defects (3) non–stoichiometric defects
1
...
They are also called
intrinsic or thermodynamic defects
...
Frenkel defects are not found in pure alkali metal
halides because cations are of large size
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Impurity Defect
It arises when foreign atoms or ions aloe present in the lattice
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When the impurity has the same charge
as the host ion
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Impurity defects can also be introduced by adding impurity ions having different charge
than host ions
...
g
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In
such cases,
Cationic vacancies produced = [number of cations of higher valence * Difference in
valence of the host cation and cation of higher valence
3
...
The
numbers of positive and negative ions present in such compounds are different from those
expected from their ideal chemical formulae
...
Types of n-stoichiometric defects are as follows:
(i) Met excess defect Metal excess defect due to anionic vacancies: Alkyl halides like NaC1
and KCl show this type of defect
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F-centres contribute colour and paramagnetic nature of
the crystal [F stands for
German wo\d Farbe meaning colour)
...
g
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On beating, it loses oxygen and turns yellow
...
Transition metals
exhibit this defect, e
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, FeO, which is found in the composition range from Fe0
...
96O
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Classification of Solids on the Basis of Electrical Conductivity
[The electricity produced on heating a polar crystal is called ‘pyroelectricity’
...
Examples Si, Ge Sn (grey), Cu2O, SiC and GaAs
...
g
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They are formed by doping
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Doping of Si
or Ge is carried out with P, As, Sb, B, Al or Ga
...
The conductivity is due to the presence of negative charge (electrons),
(ii) p·type semiconductors Silicon doped with 13 group element like gallium is called p-type
semiconductor
...
Some typical 13-15 compounds are InSb, AlP and GaAs and SOme typical 12-16
compounds are ZnS, CdS
...
These exhibit electrical and optical properties of great use in electronic industry
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1
...
g
...
2
...
g
...
3
...
g
...
4
...
moments, e
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, MnO, MnO2, FeO, etc
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Ferrimagnetic Substances
13 | P a g e
These substances have a net dipole moment due to unequal parallel and anti-parallel alignment
of magnetic moments, e
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, Fe3O4, ferrites, etc