1. 1. THE SOLID STATE
HAIZEL G. ROY
H.S.S.T. (HG) CHEMISTRY
GOVT. H.S.S. KALAMASSERY
ERNAKULAM
2. Have definite mass, volume and shape.
Intermolecular distances are short.
Intermolecular forces are strong.
Constituent particles have fixed positions.
They can only oscillate about their mean positions.
Incompressible and rigid.
GENERAL CHARACTERISTICS OF SOLIDS
3. Solids can be classified into two types. They are
Crystalline Solids
Amorphous Solids
CLASSIFICATION OF SOLIDS
5. The physical properties like electrical
resistance or refractive index show different
values when measured along different
directions in the same crystal.
The arrangement of particles is different in
different directions.
ANISOTROPY
6. The value of any physical property would
be same along any directions.
No long range order and the arrangement is
irregular along all the directions.
ISOTROPY
7. Amorphous solids have a tendency to flow very slowly.
Therefore, they are called pseudo solids or super cooled liquids.
PSUEDO SOLIDS OR SUPER COOLED LIQUIDS
8. Glass objects from ancient civilizations are milky in appearance
due to crystallization.
Glass is an amorphous solid.
On heating, glass become crystalline at some temperature.
NOTE-1
9. Glass panes fixed to windows or doors of old buildings are found to
be slightly thicker at the bottom than at the top.
Glass flows down very slowly and makes the bottom portion
slightly thicker.
NOTE-2
10. Classification is based on the intermolecular forces.
Crystalline solids are classified into four. They are
Molecular Solids
Ionic Solids
Metallic Solids
Covalent solids
CLASSIFICATION OF CRYSTALLINE SOLIDS
11. MOLECULAR SOLIDS
In molecular solids, molecules are the constituent particles.
Molecular solids are classified into three types. They are
1. Non Polar Molecular Solids
2. Polar Molecular Solids
3. Hydrogen Bonded Molecular Solids
12. The atoms or molecules are held by weak dispersion forces or
London forces.
They are Soft and non-conductors of electricity.
They have low melting points.
Exist in liquid or gaseous state at room temperature and pressure.
Eg: H2, Cl2, I2 etc.
A. NON POLAR MOLECULAR SOLIDS
13. The molecules are held together by dipole-dipole interactions.
They are soft and non-conductors of electricity.
Their melting points are higher than those of non polar molecular
solids.
Eg: Solid SO2 and Solid NH3.
B. POLAR MOLECULAR SOLIDS
14. The molecules are held together by strong hydrogen bonding.
They are non conductors of electricity.
They are generally volatile liquids or soft solids under room
temperature and pressure.
Eg: H2O.
C. HYDROGEN BONDED MOLECULAR SOLIDS
15. Ions are the constituent particles.
Formed by the 3 dimensional arrangements of
cations and anions bound by strong
electrostatic forces.
These solids are hard and brittle in nature.
They have high melting and boiling points.
They are insulators in solid state.
In aqueous solutions, they conduct electricity.
2. IONIC SOLIDS
16. Consist of +ve ions in a sea of mobile
electrons.
Held together by strong electrostatic force
of attraction.
They are malleable and ductile.
Good conductors of heat and electricity.
3. METALLIC SOLIDS
17. The atoms are held together by strong
covalent bonds.
They are very hard and brittle.
They are insulators.
Eg: Diamond, Silicon Carbide etc.
4. COVALENT OR NETWORK SOLIDS
18. Graphite is soft and conductor of electricity.
The free electrons make graphite a good
conductor of electricity.
Graphite is a soft solid and a good solid
lubricant.
Because different layers can slide one over
the other.
NOTE - 3
19. A regular 3 dimensional
arrangement of points in
space is called a crystal
lattice.
CRYSTAL LATTICE
20. Each point in a lattice is called lattice point or lattice site.
Lattice site represents one constituent particle.
The constituent particle may be an atom, a molecule or an ion.
Lattice points are joined by straight lines which give the geometry of the lattice.
CHARACTERISTICS OF CRYSTAL LATTICE
21. Unit cell is the smallest
repeating unit of a crystal
lattice which when repeated in
different direction generates
the entire crystal.
UNIT CELL
22. The dimensions are along the three edges a, b and c.
These edges may or may not be mutually perpendicular.
Angles between the edges a, b and c are α, β and γ.
A unit cell is characterized by six parameters a, b, c, α, β and γ.
CHARACTERISTICS OF UNIT CELL
30. The 14 possible 3 dimensional lattices in which the atoms are arranged to form a crystal
are called Bravais lattices.
These lattices are named after the French physicist Auguste Bravais.
BRAVAIS LATTICES
32. Simple cubic has one atom per unit cell.
Body Centered Cubic has 2 atoms per unit cell.
Face Centered Cubic unit cell has 4 atoms per unit cell.
NUMBER OF ATOMS IN A UNIT CELL
33. The number of nearest neighbour’s with which a given sphere is in
contact.
CO-ORDINATION NUMBER
34. A close packing is a way of arranging equidimensional object in
space.
The available space is filled very effectively.
CLOSE PACKED STRUCTURES
35. Each sphere is in contact with two of its neighbour’s.
The co-ordination number is 2.
CLOSE PACKING IN ONE DIMENSION
37. The particles of second, third, fourth etc
are arranged vertically with the particles
of the first row.
Each particle is in contact with four other
neighbouring particles.
So it is called square close packing.
Its co-ordination number (CN) is 4.
A. SQUARE CLOSE PACKING
38. The particles of the second row are
arranged in the depressions produced
by the particles of the first row.
The particles in the third row will be
vertically aligned with those in the
first row.
Each sphere is in contact with six other
spheres to form a hexagonal pattern.
So it is called hexagonal close packing.
Its coordination number is 6.
B. HEXAGONAL CLOSE PACKING
40. The particles of every third layer are in vertical
alignment with those of the first layer.
The third layer is a repetition of the first layer.
This will form the sequence AB AB AB AB …….
This type of packing is called AB AB packing or
hexagonal close packing (hcp).
Eg: Mg, Zn, Cd etc.
A. HEXAGONAL CLOSE PACKING
41. CO-ORDINATION NUMBER OF HCP STRUCTURE
The Each atom is positioned in the empty space
formed by
Three adjacent atoms of the top layer
Three adjacent atoms in the bottom layer
It is surrounded by six neighbouring atoms.
Thus, 12 atoms are in contact with each atom.
Hence, Co-ordination Number is 12
42. The particles of every fourth layer are in
vertical alignment with those in the first layer.
The fourth layer is the repetition of the first
layer.
This will give rise to ABC ABC ABC …………..
sequence.
This type of packing is called ABC ABC packing
or cubic close packing (ccp).
Eg: Cu, Ni, Au etc.
B. CUBIC CLOSE PACKING
43. CO-ORDINATION NUMBER OF CCP STRUCTURE
In CCP, there are three repeating layers of hexagonally
arranged atoms.
Each atom is in contact with six atoms in its own layer.
Three atoms are in contact with the layer above.
And three atoms are in contact with the layer below.
In this arrangement, each atom touches 12 of its nearest
neighbours.
Hence, Co-ordination Number is 12
44. The vacant space between the constituent particles in a closed
packed structure is called a void.
INTERSTITIAL SITES OR VOIDS
45. TYPES OF VOIDS
Voids are classified into three types. They are
Triangular Voids
Tetrahedral Voids
Octahedral Voids
46. TRIANGULAR VOID
The empty space produced in between three spheres in a close
packed structure is called a triangular void.
47. TETRAHEDRAL VOID
The void formed by the close packing of four spheres which touch
each other at only one point is called a tetrahedral void.
48. OCTAHEDRAL VOID
A void surrounded by six spheres in octahedral position is called
octahedral void.
58. In an ideal crystal the constituent particles are regularly arranged
throughout the crystal.
IDEAL CRYSTAL
IMPERFECTION
Any deviation from the completely ordered arrangement in a crystal
is called a defect or imperfection.
59. The irregularities or deviations from ideal arrangement around a
point or an atom in a crystalline substance.
POINT DEFECTS
LINE DEFECTS
The irregularities or deviations from ideal arrangement in entire
rows of lattice points.
60. TYPES OF POINT DEFECTS
Point defects can be classified into three types.
1. Stoichiometric Defects
The number of +ve and ―ve ions are exactly in the ratio indicated by the
chemical formulae.
2. Non Stoichiometric Defects
The number of +ve and ―ve ions are not exactly in the ratio indicated by the
chemical formulae.
3. Impurity Defects
This type of defect arises due to the presence of some impurities in the crystal
lattice.
63. SCHOTTKY DEFECT
Equal number of +ve and ―ve ions are missing from the lattice
site.
Found in crystals of high co-ordination number.
It decreases the density of the crystal.
Shown by ionic substances in which the cation and anion are
almost similar sizes.
The crystals are electrically neutral.
Eg: NaCl, KCl, AgBr etc.
64.
65. FRENKEL DEFECT
A cation is dislocated from its normal site to an interstitial
site.
Found in crystals having low coordination number. It does not
change the density of the solid.
Shown by ionic substances in which there is a large difference
in the size of ions.
Eg: ZnS, AgCl, AgBr and AgI
66.
67. AgBr shows both Schottky as well as Frenkel defect. Why?
The radius ratio of AgBr is intermediate.
Schottky defect arise due to missing of ions from their lattice site
Frenkel defect arise when the missing ions occupy interstitial sites.
In AgBr, Ag +
ion is small in size.
When removed from lattice site, they can occupy interstitial site.
Therefore, it shows both frenkel and schottky defect.
70. A. DUE TO ANION VACANCY
A ―ve ion may be absent from its lattice site leaving a hole.
This hole is occupied by an electron and the electrical neutrality is
maintained.
The electrons entrapped in this anion vacancy are called ‘F’ centres.
They impart colour to the crystals.
The colour is due to the excitation of electrons which absorb energy
from the visible light falling on the crystals.
Eg: Alkali halides like NaCl and KCl show this type of defect.
71.
72. When heated, the Na atoms are deposited on the surface of the crystal.
The Cl―
ions diffuse to the surface of the crystal and combine with Na
atoms to give NaCl.
This happens by the loss of electrons by Na atoms to form Na+
ions.
The released electrons diffuse into the crystal and occupy anionic sites.
As a result, the crystal now has excess of Na.
The anionic sites occupied by unpaired electrons are called F-centres.
They impart yellow colour to the crystals of NaCl.
When crystals of NaCl are heated in an atmosphere of Na vapour,
yellow colour is observed. Why?
73. B. DUE TO EXTRA CATION
An extra +ve ion occupies an
interstitial position.
The electrical neutrality is
maintained by an electron
present in another interstitial
position.
74. ZnO is white in colour at room temperature.
On heating it loses oxygen and turns yellow.
The excess Zn2+
ions move to interstitial sites.
The electrons moves to neighbouring interstitial sites.
The yellow colour is due to the Metal Excess Defect due to the presence of
Extra Cation on the interstitial position.
ZnO turns yellow on heating. Why?
76. A. DUE TO CATION VACANCY
A cation is absent from its
lattice site.
The electrical neutrality is
maintained by an extra
charge on the adjacent
metal.
77. B. DUE TO EXTRA ANION
An extra anion occupies an
interstitial position.
The electrical neutrality is
maintained by an extra charge
on the adjacent cation.
80. Conductors are substances which allow electric current to flow through it.
Metals are good conductors of electricity.
In metals, the conduction is due to the movement of electrons under the
influence of an applied electric potential.
CONDUCTORS
81. Substances which allow electric current to flow through it partially.
They have conductivity in between metals and Insulators.
SEMI CONDUCTORS
INSULATORS
These are substances which do not allow electric current to flow through
it.
82. BAND THEORY OF SOLIDS
Valence band is occupied by valence electrons.
Conduction band is the empty band above the valence band.
83. CONDUCTORS
In a conductor, valence band overlaps the conduction band.
Therefore, no energy is required to move an electron from the valence
band to the conduction band.
84. SEMI CONDUCTORS
In In semiconductors, the gap between the valence band and
conduction band is small.
Therefore, some electrons may jump from valence band to conduction
band
It shows some conductivity.
85. INSULATORS
In an insulator, the valence band and conduction bands are not
overlapped.
There is a large gap in between the valence and conduction
bands.
The electrons cannot jump from the valence band to
conduction band.
86.
87. INTRINSIC SEMICONDUCTOR
Semiconductors in their extremely pure state are very poor conductors of
electricity.
They are called intrinsic semiconductors.
Eg: Ge, Si.
EXTRINSIC SEMICONDUCTOR
With the addition of certain other elements in the crystal structure of
semiconductors, their conductivity can be improved.
They are called extrinsic semiconductors.
CLASSIFICATION OF SEMICONDUCTORS
88. DOPING
The process of adding certain impurities in the crystal structure
of a semiconductor to improve its conductivity is called doping.
89. N-TYPE SEMI CONDUCTOR
A semiconductor crystal having an excess of electrons by doping.
The donor atoms are 15th group elements like P, As, Sb, Bi.
Electrons are the charge carriers.
When a pure semiconductor is doped by pentavalent impurity (P,
As, Sb, Bi) then, 4 electrons out of 5 valence electrons bonds with
the four electrons of Ge or Si.
The fifth electron of the dopant is set free.
The impurity atom donates a free electron for conduction in the
lattice and is called “Donor”.
Eg. Silicon dopped with P, As, Sb and Bi.
Eg: Germanium dopped with P, As, Sb and Bi.
90. A semiconductor material having an excess of holes by doping.
Holes are the charge carriers.
The donor atoms are 13th group elements like B, Al, Ga, In and
Tl (Trivalent Impurity).
When a pure semiconductor is doped with a trivalent impurity
then, the three valence electrons of the impurity bonds with
three of the four valence electrons of the semiconductor.
This leaves an absence of electron (hole) in the impurity.
These impurity atoms which are ready to accept bonded
electrons are called “Acceptors”.
Eg: Silicon dopped with Boron, Silicon dopped Aluminium,
Germanium dopped with Boron etc.
P-TYPE SEMI CONDUCTOR
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92. PARAMAGNETISM
Substances which are weakly attracted by the magnetic field.
Paramagnetism is due to the presence of one or more unpaired
electrons which are attracted by the magnetic field.
Eg: Al, O2, TiO, CuO, Cu2+, Fe3+, Cr3+ etc.
93. Substances which are weakly repelled by the magnetic field
are called diamagnetic substances.
Shown by those substances in which all the electrons are
paired and there are no unpaired electrons.
Eg: H2O, Alcohol, C6H6, NaCl etc.
DIAMAGNETISM
94. The substances which are strongly attracted by the magnetic
field are known as ferromagnetic substances.
They show permanent magnetism even when the magnetic
field is removed.
The magnetic moments are in the same direction.
Eg: Fe, Co, Ni, Gd, CrO2 etc.
FERROMAGNETISM
95. Alignment of magnetic moments in the opposite direction in
equal numbers.
It results in zero magnetic moment and gives rise to
antiferromagnetism.
Eg: MnO, FeO, CoO etc.
ANTIFERROMAGNETISM
96. The magnetic moments are aligned in parallel and antiparallel
directions in unequal numbers.
It results in a net magnetic moment.
Eg: Fe3O4, MgFe2O4, CuFe2O4, ZnFe2O4 etc.
FERRIMAGNETISM
97. Curie point or Curie Temperature is the temperature at which certain magnetic
materials undergo a sharp change in their magnetic properties.
Above this temperature, the magnetic materials lose their ferromagnetic
properties.
At lower temperatures, the magnetic dipoles are aligned.
Above the curie temperature, random thermal motions cause misalignment of
the dipoles.
CURIE TEMPERATURE
