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Title: The Solid State
Description: The correlation between structure and properties helps in discovering new solid materials with desired properties like …… high temperature superconductors, magnetic materials, biodegradable polymers for packaging, bio-compliant solids for surgical implants, etc.
Description: The correlation between structure and properties helps in discovering new solid materials with desired properties like …… high temperature superconductors, magnetic materials, biodegradable polymers for packaging, bio-compliant solids for surgical implants, etc.
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7/8/2013
CHEMISTRY
Navrachana School, Sama
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Zaid Mansuri
1
The correlation between structure and properties helps in
discovering new solid materials with desired properties
like ……
high temperature
superconductors,
magnetic materials,
biodegradable polymers for packaging,
bio-compliant solids for surgical implants, etc
...
...
Zaid
Mansuri
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1
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(ii) Intermolecular distances are short
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(iv) Their constituent particles (atoms, molecules or ions)
have fixed positions and can only oscillate about their
mean positions
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1
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On heating Amorphous
crystalline at some temperature
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Navrachana School, Sama
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Zaid Mansuri
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b
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Window panes are thicker at bottom !
Crystalline solids are Anisotropic
i
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some of their physical properties like
electrical resistance or
refractive index
show different values when measured along
different directions in the same crystals
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Mansuri
Navrachana School, Sama
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Suming up
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1
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www
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wordpress
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There are only 14 possible three dimensional lattices
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(b) Each point in a crystal lattice represents one constituent particle which may be
an atom, a molecule (group of atoms) or an ion
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Unit cell : is the smallest portion of a crystal
lattice which, when repeated in different
directions, generates the entire lattice
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perpendicular
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one or more constituent particles at
positions other than corners in addition to
those at corners, it is called
a centered unit cell
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5 Number of Atoms in a Unit Cell
17
Shows
contribution of
each sphere
1
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1 Primitive
Cubic Unit Cell
Only centre of
sphere and not
actual size
Actu
al
size
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5
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5
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(a) Close Packing in
1D
C
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= 2
(b) Close Packing in
2D
C
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= 4
C
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= 6
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(c) Close Packing in 3D
(i) Square close-packed in
3D
AAAAAA…
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2N
tetrahedral voids
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(b) Placing third layer over the second layer
Covering Tetrahedral Voids:
ABABAB…
...
(ccp or fcc)
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Covering octahedral voids
ABCABC…
ccp
Covering tetrahedral voids
ABAB…
hcp
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6
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of tetrahedral voids = 1 x 8 =
8
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Octahedral voids in ccp / fcc
at edge centre :
at body centre :
¼ x 12 = 3
1x1=1
Navrachanavoids
School, Sama
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of octahedral
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Summing up …
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e
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e
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1 A compound is formed by two elements X and Y
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What is the formula of the
compound?
Ans : XY
Example 1
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What is the formula of the compound formed
by the elements A and B?
Ans : A4B3
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7 Packing Efficiency
What is packing efficiency?
Packing efficiency is the percentage of total space filled by the particles
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of the unit cell
100%
Vol
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occupied by the spheres in the unit cell
total vol
...
...
7 Packing Efficiency
1
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1 Packing Efficiency in hcp
and
ccp
Structures
74%
Packing efficiency = vol
...
of the unit cell
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7
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occupied by 2 spheres in the unit cell x 100 %
total vol
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7
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4 %
Packing efficiency = vol
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of the unit cell
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8 Calculations Involving Unit Cell Dimensions
Density of the unit cell, d = mass of the unit cell
volume of the unit cell (v)
= z
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M
a3 NA
, z = no
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3
35
An element has a body-centred cubic (bcc) structure with a cell edge
of 288 pm
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2 g/cm3
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of small crystals
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Line defects : are the irregularities
or deviation from ideal arrangement
in entire row
Point defects : are the irregularities
or deviation from ideal arrangement
around a point or an atom
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Crystal defects
Line defects
Point defects
Stoichiometric
defects
These are the point defects
that do not disturb the
stoichiometry of the solid
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Impurity defects
Metal excess defects
Non-Stiochiometic
defects
Metal deficient defects
Due to anionic
vacancies
1
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Interstitial defects
Due to extra cations
in the interstital
3
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Schottky defects
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Vacancy defects
When some of the lattice sites are vacant, the crystal is said to
have vacancy defect (Fig
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23)
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-This defect can also develop when a substance is heated
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Interstitial defects
When some constituent particles (atoms or molecules) occupy
an interstitial site, the crystal is said to have interstitial defect
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Note : Ionic solids must always maintain electrical neutrality
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3
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- It creates a vacancy defect at its original site and an interstitial
defect at its new location
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- density of the solid does not change
...
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Schottky defects
41
In this defect equal number of cations and anions are missing from
their positions
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- Electrical neutrality is maintained
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In 1 cm3 there are about 1022 ions
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- shown by ionic substances in which the cation and anion are of
almost similar sizes
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- Note : AgBr shows both, Frenkel as well as Schottky defects
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Impurity defects
When some foreign impurities replace the ions of the
crystal, the crystal is said to have Impurity defect
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g : SrCl2 in NaCl
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One site is occupied while other remains vacant (cationic vacancy)
...
of cationic vacancies are generated in this case
...
g : CdCl2 + AgCl solid solution
Foreign ion
Vacancy
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Metal excess defects
Due to anionic
vacancies
e
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...
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Metal excess defects
Due to extra cations
in the interstital
ZnO
White
---
Zn+2 + ½ O2 + 2eyellow
- O is lost as O2 reversibly
...
- thus, Zn1+xO
Metal deficient defects
Many solids – difficult to prepare in stoichiometric composition
- More anions than metals
- Fe0
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96O
- some Fe+2
Fe+3 + e- to maintain the electrical neutrality of the crystal
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1
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Band : the atomic orbitals of metal atoms form molecular orbitals which are
so close in energy to each other as to form a band
...
...
can
can be
be increased
increased
by adding suitable
Impurities ( Doping)
Electronic defects
Electron deficient impurities
Electron rich impurities
Si (gr
...
15)
Si (gr
...
13)
Navrachana School, Sama
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• photo-diode
solar cells
• Combination of different group atoms to give average of 4e-s
gr
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16
e
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13 + gr
...
g: InSb, AlPb and GaAs
have very fast
response
• In these compounds, the bonds are not perfectly covalent and the ionic
character depends on the electronegativities of the two elements
...
VO, VO2, VO3 and TiO3 show metallic or insulating properties
depending on temperature
...
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11 Magnetic properties
Every substance
magnetic properties
due to e-s
behave like
tiny magnets
Magnetic moment
Spin motion
Orbital motion
• Electron being a charged particle and undergoing these motions can be considered
as a small loop of current which possesses a magnetic moment
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Bohr magneton,
2
µB = 9
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field
e
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• eg: H2O, NaCl and C6H6
• They are weakly magnetised in a magnetic field in opposite direction
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• Pairing of electrons cancels their magnetic moments and they lose their
magnetic character
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Ferromagnetism:
• A few substances like iron, cobalt, nickel, gadolinium and CrO2 are attracted
very strongly by a magnetic field
...
• can be permanently magnetised
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Thus, each domain acts as a tiny
magnet
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When the
substance is placed in a magnetic field all the domains get oriented in the
direction of the magnetic field and a strong magnetic effect is produced
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Antiferromagnetism:
• Substances like MnO showing antiferromagnetism have domain structure similar to
ferromagnetic substance, but their domains are oppositely oriented and cancel out each
other's magnetic moment
Navrachana School, Sama
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• weakly attracted by magnetic field as compared to ferromagnetic substances
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• These substances also lose ferrimagnetism on heating and become paramagnetic
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Title: The Solid State
Description: The correlation between structure and properties helps in discovering new solid materials with desired properties like …… high temperature superconductors, magnetic materials, biodegradable polymers for packaging, bio-compliant solids for surgical implants, etc.
Description: The correlation between structure and properties helps in discovering new solid materials with desired properties like …… high temperature superconductors, magnetic materials, biodegradable polymers for packaging, bio-compliant solids for surgical implants, etc.