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Solid State Chemistry
TEACHER’S ORIENTATION
Some important terms and defination
Anisotropy- the property due to which crystals shows different physical properties
(eg.opticals properties, magnetic properties) in different planes of crystal, is called anisotropy.
Isotropy- the property due to which crystals shows some physical properties in all directions
is called isotropic.
Eg. All
amorphous solids are isotropic.
``
Lattice- a three dimensional regular arrangement of atoms molecules or ions are called lattice.
Unit cell- the smallest unit which repeats to form a lattice is unit cell.
Three types of unit cells with properties
Types of unit cell
definations No. of atoms/unit
cell=z
Relation
between r&a
Packing
efficiency
Simple
cubic/Primitive
Lattice
point are
present at
corners of
cube
Lattice
point are
present at
corners&
body of
cube
Lattice
point are
present at
corners
&faces of
cube
1/8×8=1
that is Z=1
r =a/2
52.5%
1/8×8=1
01 in body
Z=1+1=2
r= √3 a/4
68%
1/8×8=1
1/2×6(faces)=3
Z=1+3=4
R=
74%
B.C.C
FCC
√2a/4
ectlt Lesson plan
Solid State Chemistry
VoidsTwo
types of voids.
Tetrahedral
Octahedral
In this types of voides the centre of
atoms/
In these types of voids the centre of
atoms/ions lies at the corners of
octahedron.
ions (spheres) lies at corners of regular
regular tetra hedron.
Co-ordination number of void is 6.
No. of octaldnal void
Cordinator number of void is 4.
=No. of atom/ions(spheres) in Lattice
No. of tetraledial void is twice the
i.e. N is the no.of closed packed spheres
no. of atoms/ions(spheres) lattice
then n no. of void =N
i.e if v is the no. of close packed spheres.
Radius ratio for ionic crystall
2n is the of octahedial void.
r+/r- = 0.414-0.732
Radius ratio for ionic crystalls.
r/r =0.414 to 0.225
Density =d
d= Z×M/ a³×Na
Z = no. of atoms per unit cell
M = atomic/ molecular mass a = edge length
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Solid State Chemistry
Na= Avogadro’s no.
Z = no. of lattice point per unit cell
a = Edge length of lube
r = radius of lattice point (atom or ion)
Packing efficiency = volume occupied by atoms/ ions in unit cell/total volume of unit cell × 100 in two
dimension
-
1) Square close packing
2) Hexagonal close
packing
Hexagonel close
packing
Square close
packing
Hexagonal
square
Central atom is surrounded by 4 athoms
Marked as (1,2,3,4) ie.
spheres are in
1,2,3,4 are is in intimate contact with
central atom has coordination number 4
number6
Central atom is surrounded by 6 athoms
Marked as (1,2,3,4,5,6) all these
intimate contact with central atom
central atom has coordination
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Solid State Chemistry
Square close packing:Central atom is surrounded by four other atoms marked as (1,2,3,4) i.e 1,2,3,4 are in intimate
contact with central atom.
Coordination number = 4.
Hexagonal close packing:Central atom is surrounded by six other atoms marked as (I,II,3,4,5,6) all these spheres are in
intimate contact with central atom.
Coordination number = 6
Packing in three dimention
Simple cubic packing
Hexagonal close packing
A
Cubic close packing
A
A
B
A
B
A
C
A
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Solid State Chemistry
STUDENT’S ORIENTATION
Defects in crystals and Band Theory of Conduction
Point Defect
Stoichiometric
Line Defect
Non- Stoichiometric
Impurity
Defect
1a) Frankel defect
- Metal excess defects
1b) Schottky defect
(due to anionic vacancies)
1c) Vacancy defect
- Metal excess defect
1d) Interstitial defect
(due to presence of extra cations)
Stoichiometric defect:- The point defect in which stoiciometriy of solids are not disturbed.
Non stoichoimetric defect:- The point defect in which the stoichiometry of solids are essential
disturbed.
Impurity Defect:- The defects which arises due to mixing impurity into solid crystall.
Eg: When Srcl 2 / Cacl 2 is mixed in molten Nacl then some of the sites of Na+ are occupied by Sr
+2. Since Sr +2 is bivalent it replaces 2Na + ions out of 2 sites. One is occupied by Sr+ other remains
vacant creating impurity defect.
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Solid State Chemistry
CONCEPT DETAILS
1a) Schottky defect :- the defect in which pairs of cations and anion are missing from its original
crystall site is called schottky defect .
Note
 This defect can be seen when cations and anions are of comparable size.
Eg is Nacl,AgBr, kcl etc
1b) Frankel defect :- the defect in which cations (smaller size) laeves its original site and slips
into interstitial void such defect is known as frankel defect.
1c) Vacancy defect :- when some of the sites are vacant the crystall is said to be develop vacancy
defect aslo called thermodynamic defect
- Schottky defect belong to this category
- This defect leads to decrease in density
1d) Interstitial defect:- when interstitial site are occupied by some constituent particle the
crystal’s is said to develop interstitial defect
- This defect leads to increase in density
F centre – A point defect shown by alkali metal halide if heated in presence of alkali. Electron loosed by
alkali metal gets trapped in the crystal which then exhibits colour in the visible region due to excitation
of electron
NaCl heated in presence of Na ------- yellow colour
KCl heated in presence of K ------- violet colour
LiCl heated in presence of Li ------- pink colour
(ii) Metal excess defect :- generally shown by zinc oxide on heating acquires colour due to loss of
oxygen. Zinc ions goes to interstitial void an electrons to neighboring void exhibiting colour .
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Solid State Chemistry
(iii) Metal deficiency defect :- Insuch type of defect metal is deficient and charge neutrality is maintained
by acquiring higher oxidation state by some of the metal presnt in crystal . This defect is shown by oxide
of transition elements because they have the ability to exist in variable oxidation state. egFe0.93O,
Ni0.98O.
Electrical properties of solids

Conduction of electricity in solids.
 Band Theory







The atomic orbitals of metals atoms forms molecules orbital which is very close to each
other and forms a band.
If the band is filled (occupied) it is called Valence band.
If the bond is unoccupied it is called conduction band.
Energy band between two bands are called forbidden zone.
In conductors there is no low energy gap between valence band and conductor band. So
electron can easily jump from valence band to conduction band and that is why metal shows
conductivity.
In insulator energy gap between valance band and conduction band is high. So electrons can
not flow easily so it behaves as insulator.
In semiconductor energy gap between valance band and conduction band is intermediate as
in conductors and insulators. So some electrons can jump from V.B. to C.B. and it behaves as
semiconductors.
Magnetic Properties –
*Ferromagnetic substance- Those substance in which magnetic domains are aligned in parallel direction.
Eg:- Iron, Cobalt , Nickel.
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Solid State Chemistry
-
These substances can be permanently Magnetized .
They are strongly attracted by Magnets.
*Ant ferromagnetic substance- Those substance in which Magnetic domains are alligned in antiparallel
direction and they are in equal number.
Eg:- MnO
*Ferrimagnetic substances- Those substances in which Magnetic domains are alligned in parallel and
antiparallel direction in unequal number.
*Paramagnetic substance- Those substance in which is weakly attracted by Magnetic field. These
substances have unpaired electron in their orbital.
Eg:- O2 ,CO+2, Fe+3, Cr+3
-They are magnetised in magnetic field.
*Diamagnetic substances- that substance which is weekly repelled by magnetic field. Those substances
have paired electron in their orbital.
Eg:- H2O, Nacl, C6H6
-They are weakly magnetised by magnetic field.
Pyroelectricity :- It is a phenomena of producing electricity when any pyroelectric substance is heated
Piezoelectricity;- It is a phenomena of producing electricity when any piezoelectric substance is
subjected to any mechanical stress or vice versa eg:-quartz
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Solid State Chemistry
Questions: LEVEL 1
1. Li heated with Licl gave pink colour. Why?
Ans:- Due to formation of “F” center.
2. Which point defect does not involve change in density?
Ans:- Frankel Defect.
3. Why F.C.C is also called C.C.P?
Ans:- Because in FCC the packing efficiency is highest i.e. 74% in which spheres are packed very close
to each other.
4. What will be coordination number of an atom in a)hcp b) BCC
Ans:- a) 12 b) 8
5. Nacl doped with Mgcl2. Name the defect that will arise?
Ans:- Impurity defect
6. Nacl doped with 10/1000 mol % of Alcl3. Calculate the conc. of cation vacancies.
Ans:- 10/1000 mol %= 10/100000 mol
1 Al+3 will produce= 2×cation vacancy
Questions LEVEL 2
Q.1 What is coordination number of a metal atom in ccp structure ?
Q.2 How can a ferromagnetic substance be changed to a paramagnetic one?
Q.3 What is the Frenkel defect ?
Q.4 What is the difference between glass and quartz, though both contain Silicate units?
Q.5 Which solid is likely to be the best material for converting sunlight into electricity?
Q.6 How is ferromagnetism different from Para magnetism?
Q.7 Solid solution of group 13 or 15 impurities with group 14 elements is to found to exhibit unusual
electrical properties. Why?
Questions: LEVEL 3
Q.5 The following to graph represent conductivity as a function of temperature. Giving reason
explain the type of
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Solid State Chemistry
substances.
Conductivity
Conductivity
Temp
Temp
Diagnostic tool
1.
2.
3.
4.
5.
Old building glasses becomes thicker at the bottom, why?
Glass is not considered as true solid, Why?
Old civilization glasses are opaque, Why?
On broken a glass it surfaces are not smooth, Why?
Generally NaCl is white but on heating in the vapoures of Na it shows yellow
coloure,Why
HOME ASSIGNMENT
Formative Assessment :
Q.1 Lithium metal crystal has body centered cubic structure. Its density is 0.53 g cm/3 and its
molar mass is 6.94 g mol/1. Calculate the cation vacancies per mole. [NA = 6.023×1023]
Q.2 What is meant by (i) 12-16 compound and (ii) 13 – 15 compound ? Give examples.
Q.3 Gold (atomic radius = 0.144 nm) crystallizes in a face centered unit cell. What is the length of a
side of the cell ?
Q.4 Silver forms ccp lattice and X-ray studies of its crystals show that the edge length of its unit cell
its 408.6pm. Calculate the density of silver (A Atomic mass = 107.9u)
Q.5 An element with molar mass 2.7×10-2 kg mol -1 forms a cubic unit cell with edge length 405pm. If
its density is 2.7×103 kg m-3, what is the nature of the cubic unit cell ?
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Solid State Chemistry
Three mark questions:Q.1 Assign reason of the following:
(i) Phosphorus doped slicon is a semiconductor.
(ii) Schottky defect lowers the density of a solid.
Q.2 (a) Determine the type of cubic lattice to which a given crystal belongs if it has edge length of
290 pm and density is 7.80 g /cm/3 (Molecular mass = 56 g/ mol)
(b) Why does zinc oxide exhibit enhanced electrical conductivity on heating ?
Q.3 List out the defects with following property .
(i) Defects causing change in conductivity.
(ii) Defect causing change in density.
Assignment
Level I :- Q1.What is the effect of Schottky and Frankel defects on the density of crystalline
solids?
Q.2 Name an element with which germanium can be doped to produce an n-type semiconductor.
Q.3 Why is potassium chloride sometimes violet instead of pure white?
Q.4 Define the term ‘amorphous’.
LevelII- Q.1Explain the following terms with suitable example :-
(i) Ferri magnetism
(ii) n – type semi conductor
(iii) Forbidden zone.
Q.2 Calculate the distance between Na+ and Cl – in NaCl crystal if its density is 2.165gm/cm3. [molar
mass of NaCl is 58.5gm/mol]
Q.3 Schottky defect generate an equal number of cation and anion vacancy while doping produces
only cation vacancy.
Level III:
Q.1 Refractive index of a solid is observed to have the same value alon all direction. Comment on
the nature of solid. Would it show cleavage property?
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Solid State Chemistry
Q.2 Some of the very old glass objects appear slightly milky instead of being transparent. Explain
why?
Q.3 Explain the deference between conductivity of sodium and magnesium.
Project:1Prepare the model of different types of crystals by using transparent glass
2.Prepare model of simple unit cell, body centred and Face centred unit calculate the ratio
between spheres and voids