Solid State JEE Notes | EduRev

JEE : Solid State JEE Notes | EduRev

 Page 1


1 . INTRODUCTION :
Matter can exist in three physical states namely ; solid, liquid and gas. Matter consists of tiny particles
(atoms, ions or molecules). If the particles are very far off from one another, they behave like gases; nearer,
they behave like liquids, and nearest, like solids. The three states of matter are thus known as the three
states of aggregation from Latin word meaning "Flacking together".
The fundamental difference between the three states of aggregation lies essentially in the difference of the
relative amounts of energy possessed by the particles in the three states. The relative energies in the
different states of matter are governed by two universal opposing tendencies associated with the particles :
(i) They have tendency of mutual attraction.
(ii) They have tendency of escape from one another which is known as escaping tendency.
Whether a given system would exist as a solid, liquid or gas depends upon the relative strengths of these
opposing tendencies. If the escaping tendency is greater than the attraction between them, the molecules
will be carried far from each other to distances which are large as compared with their diameters, the system
will exists in gaseous state. But in the liquid state the molecular attraction exceeds the escaping tendency
and in the solid state the forces of attraction are so much greater than those of escaping tendency that each
particle is bound into a definite place in a rigid position by the mutual attraction of molecules. In other
words, in the solid state, the system possesses the amount of energy of motion i.e. kinetic energy.
2 . THE SOLID STATE :
The solid are characterised by incompressibility, rigidity and mechanical strength. The molecules, atoms or
ions in solids are closely packed i.e. they are held together by strong forces and can not move about at
random. Thus solids have definite volume, shape, slow diffusion, low vapour pressure and possesses the
unique property of being rigid. Such solids are known as true solids e.g. NaCl, KCl, Sugar, Ag, Cu etc. On
the other hand the solid which loses shapes on long standing, flows under its own weight and easily distorted
by even mild distortion forces are called pseudo solids e.g. glass, pitch etc.
Some solids such as NaCl, Sugar, Sulphur etc. have properties not only of rigidity and incompressibility but
also of having typical geometrical forms. These solids are called as crystalline solids. In such solids there is
definite arrangements of particles (atoms, ions or molecules) throughout the entire three dimensional network
of a crystal. This is named as long-range order. This three dimensional arrangement is called crystal
lattice or space lattice. Other solids such as glass, rubber, plastics etc. have rigidity and incompressibility
to a certain extent but they do not have definite geometrical forms or do not have long range order are
known as amorphous solids.
3 . DIFFERENCES BETWEEN CRYSTALLINE AND AMORPHOUS SOLIDS :
( i ) Characteristic Geometry : In the crystalline solids the particles (atoms, ions, or molecules) are
definitely and orderly arranged thus these have characteristic geometry while  amorphous solids do
not have characteristic geometry.
(i i) Melting Points : A crystalling solids has a sharp melting point i.e. it changes into liquid state at a
definite temperature. On the contrary an amorphous solid does not has a sharp melting point. For
example, when glass is heated,  it softens and then starts flowing without undergoing any abrupt or
sharp change from solid to liquid state. Therefore, amorphous solids are regarded as "liquids at all
temperatures".
(iii) Cooling curve : Amorphous solids show smooth cooling curve while crystalline solids show two
breaks in cooling curve. In the case of crystalline solids two breaks points 'a' and 'b' are appear. These
points indicate the beginning and the end of the process of crystallization. In this time interval temperature
remains constant. This is due to the fact that during crystallisation process energy is liberated which
compensates for the loss of heat thus the temperature remains constant.
THE SOLID STATE
JEEMAIN.GURU
Page 2


1 . INTRODUCTION :
Matter can exist in three physical states namely ; solid, liquid and gas. Matter consists of tiny particles
(atoms, ions or molecules). If the particles are very far off from one another, they behave like gases; nearer,
they behave like liquids, and nearest, like solids. The three states of matter are thus known as the three
states of aggregation from Latin word meaning "Flacking together".
The fundamental difference between the three states of aggregation lies essentially in the difference of the
relative amounts of energy possessed by the particles in the three states. The relative energies in the
different states of matter are governed by two universal opposing tendencies associated with the particles :
(i) They have tendency of mutual attraction.
(ii) They have tendency of escape from one another which is known as escaping tendency.
Whether a given system would exist as a solid, liquid or gas depends upon the relative strengths of these
opposing tendencies. If the escaping tendency is greater than the attraction between them, the molecules
will be carried far from each other to distances which are large as compared with their diameters, the system
will exists in gaseous state. But in the liquid state the molecular attraction exceeds the escaping tendency
and in the solid state the forces of attraction are so much greater than those of escaping tendency that each
particle is bound into a definite place in a rigid position by the mutual attraction of molecules. In other
words, in the solid state, the system possesses the amount of energy of motion i.e. kinetic energy.
2 . THE SOLID STATE :
The solid are characterised by incompressibility, rigidity and mechanical strength. The molecules, atoms or
ions in solids are closely packed i.e. they are held together by strong forces and can not move about at
random. Thus solids have definite volume, shape, slow diffusion, low vapour pressure and possesses the
unique property of being rigid. Such solids are known as true solids e.g. NaCl, KCl, Sugar, Ag, Cu etc. On
the other hand the solid which loses shapes on long standing, flows under its own weight and easily distorted
by even mild distortion forces are called pseudo solids e.g. glass, pitch etc.
Some solids such as NaCl, Sugar, Sulphur etc. have properties not only of rigidity and incompressibility but
also of having typical geometrical forms. These solids are called as crystalline solids. In such solids there is
definite arrangements of particles (atoms, ions or molecules) throughout the entire three dimensional network
of a crystal. This is named as long-range order. This three dimensional arrangement is called crystal
lattice or space lattice. Other solids such as glass, rubber, plastics etc. have rigidity and incompressibility
to a certain extent but they do not have definite geometrical forms or do not have long range order are
known as amorphous solids.
3 . DIFFERENCES BETWEEN CRYSTALLINE AND AMORPHOUS SOLIDS :
( i ) Characteristic Geometry : In the crystalline solids the particles (atoms, ions, or molecules) are
definitely and orderly arranged thus these have characteristic geometry while  amorphous solids do
not have characteristic geometry.
(i i) Melting Points : A crystalling solids has a sharp melting point i.e. it changes into liquid state at a
definite temperature. On the contrary an amorphous solid does not has a sharp melting point. For
example, when glass is heated,  it softens and then starts flowing without undergoing any abrupt or
sharp change from solid to liquid state. Therefore, amorphous solids are regarded as "liquids at all
temperatures".
(iii) Cooling curve : Amorphous solids show smooth cooling curve while crystalline solids show two
breaks in cooling curve. In the case of crystalline solids two breaks points 'a' and 'b' are appear. These
points indicate the beginning and the end of the process of crystallization. In this time interval temperature
remains constant. This is due to the fact that during crystallisation process energy is liberated which
compensates for the loss of heat thus the temperature remains constant.
THE SOLID STATE
JEEMAIN.GURU
( i v) Isotropy and Anisotropy : Amorphous solids differ from crystalline solids and resemble liquids in
many respects. The properties of amorphous solids, such as electrical conductivity, thermal conductivity,
mechanical strength, refractive index, coefficient of thermal expansion etc. are same in all directions.
Such solids are known as isotropic. Gases and liquids are also isotropic.
On the other hand crystalline solids show these physical properties different in diferent directions.
Therefore crystalline solids are called anisotropic. The anisotropy itself is a strong evidence for the
existence of orderly molecular arrangement in  crystals. For example, the velocity of light passing
through a crystal is different in different directions. A ray of light entering in a crystal may split up into
two components each following a different path and travelling with a different velocity.
This phenomenon is called double refraction. In the figure
two different kinds of atoms are shown in two dimensional
arrangement. If the properties are measured along the
direction CD, they will be different from those measured
along the direction AB. This is due to the fact that in the
direction AB each row is made up of one type of atoms
while in the direction CD each row is made up of two types
of atoms. It is important of note that in the case of
amorphous solids, liquids and gases atoms or molecules are
indentical and all properties are same in all directions.
( v ) Cutting :
Crystalline solids give clean cleavage while amorphous solids give irregular cut, due to conchoidal
fracture on cutting with a sharp edged tool.
4 . CRYSTALLINE STATE :
"A crystal is a solid composed of atoms (ions or molecules) arranged in an orderly repetitive array".
Most of the naturally occuring solids are found to have definite crystalline shapes which can be recognised
easily. These are in large size because these are formed very slowly thus particles get sufficient time to get
proper position in the crystal structure. Some crystalline solids are so small that appear to be amorphous.
But on examination under a powerful microscope it is also seen to have a definite crystalline shape. Such
solids are known as micro crystalline solide. Thus the crystallinity of a crystal may be defined as "a condition
of matter resulting from an or orderly, cohesive, three dimensional arrangement of its component particles
(atoms, ions or molecules) in space". This three dimensional arrangement is called crystal lattice or space
lattice. The position occupied by the particles in the crystal lattice are called lattice sites or lattice points. The
lattices are bound by surface that usually planar and known as faces of the crystal.
"The smallest geometrical position of the crystal which can be used as repetitive unit to build
up the whole crystal is called a unit cell."
Cooling curve of crystalline solid Cooling curve of an amorphous solid
Time Time
Temperature
Temperature
b
a
c
c indicate super cooled
liquid state
B
D
C A
Anisotropic behaviour of crystals
JEEMAIN.GURU
Page 3


1 . INTRODUCTION :
Matter can exist in three physical states namely ; solid, liquid and gas. Matter consists of tiny particles
(atoms, ions or molecules). If the particles are very far off from one another, they behave like gases; nearer,
they behave like liquids, and nearest, like solids. The three states of matter are thus known as the three
states of aggregation from Latin word meaning "Flacking together".
The fundamental difference between the three states of aggregation lies essentially in the difference of the
relative amounts of energy possessed by the particles in the three states. The relative energies in the
different states of matter are governed by two universal opposing tendencies associated with the particles :
(i) They have tendency of mutual attraction.
(ii) They have tendency of escape from one another which is known as escaping tendency.
Whether a given system would exist as a solid, liquid or gas depends upon the relative strengths of these
opposing tendencies. If the escaping tendency is greater than the attraction between them, the molecules
will be carried far from each other to distances which are large as compared with their diameters, the system
will exists in gaseous state. But in the liquid state the molecular attraction exceeds the escaping tendency
and in the solid state the forces of attraction are so much greater than those of escaping tendency that each
particle is bound into a definite place in a rigid position by the mutual attraction of molecules. In other
words, in the solid state, the system possesses the amount of energy of motion i.e. kinetic energy.
2 . THE SOLID STATE :
The solid are characterised by incompressibility, rigidity and mechanical strength. The molecules, atoms or
ions in solids are closely packed i.e. they are held together by strong forces and can not move about at
random. Thus solids have definite volume, shape, slow diffusion, low vapour pressure and possesses the
unique property of being rigid. Such solids are known as true solids e.g. NaCl, KCl, Sugar, Ag, Cu etc. On
the other hand the solid which loses shapes on long standing, flows under its own weight and easily distorted
by even mild distortion forces are called pseudo solids e.g. glass, pitch etc.
Some solids such as NaCl, Sugar, Sulphur etc. have properties not only of rigidity and incompressibility but
also of having typical geometrical forms. These solids are called as crystalline solids. In such solids there is
definite arrangements of particles (atoms, ions or molecules) throughout the entire three dimensional network
of a crystal. This is named as long-range order. This three dimensional arrangement is called crystal
lattice or space lattice. Other solids such as glass, rubber, plastics etc. have rigidity and incompressibility
to a certain extent but they do not have definite geometrical forms or do not have long range order are
known as amorphous solids.
3 . DIFFERENCES BETWEEN CRYSTALLINE AND AMORPHOUS SOLIDS :
( i ) Characteristic Geometry : In the crystalline solids the particles (atoms, ions, or molecules) are
definitely and orderly arranged thus these have characteristic geometry while  amorphous solids do
not have characteristic geometry.
(i i) Melting Points : A crystalling solids has a sharp melting point i.e. it changes into liquid state at a
definite temperature. On the contrary an amorphous solid does not has a sharp melting point. For
example, when glass is heated,  it softens and then starts flowing without undergoing any abrupt or
sharp change from solid to liquid state. Therefore, amorphous solids are regarded as "liquids at all
temperatures".
(iii) Cooling curve : Amorphous solids show smooth cooling curve while crystalline solids show two
breaks in cooling curve. In the case of crystalline solids two breaks points 'a' and 'b' are appear. These
points indicate the beginning and the end of the process of crystallization. In this time interval temperature
remains constant. This is due to the fact that during crystallisation process energy is liberated which
compensates for the loss of heat thus the temperature remains constant.
THE SOLID STATE
JEEMAIN.GURU
( i v) Isotropy and Anisotropy : Amorphous solids differ from crystalline solids and resemble liquids in
many respects. The properties of amorphous solids, such as electrical conductivity, thermal conductivity,
mechanical strength, refractive index, coefficient of thermal expansion etc. are same in all directions.
Such solids are known as isotropic. Gases and liquids are also isotropic.
On the other hand crystalline solids show these physical properties different in diferent directions.
Therefore crystalline solids are called anisotropic. The anisotropy itself is a strong evidence for the
existence of orderly molecular arrangement in  crystals. For example, the velocity of light passing
through a crystal is different in different directions. A ray of light entering in a crystal may split up into
two components each following a different path and travelling with a different velocity.
This phenomenon is called double refraction. In the figure
two different kinds of atoms are shown in two dimensional
arrangement. If the properties are measured along the
direction CD, they will be different from those measured
along the direction AB. This is due to the fact that in the
direction AB each row is made up of one type of atoms
while in the direction CD each row is made up of two types
of atoms. It is important of note that in the case of
amorphous solids, liquids and gases atoms or molecules are
indentical and all properties are same in all directions.
( v ) Cutting :
Crystalline solids give clean cleavage while amorphous solids give irregular cut, due to conchoidal
fracture on cutting with a sharp edged tool.
4 . CRYSTALLINE STATE :
"A crystal is a solid composed of atoms (ions or molecules) arranged in an orderly repetitive array".
Most of the naturally occuring solids are found to have definite crystalline shapes which can be recognised
easily. These are in large size because these are formed very slowly thus particles get sufficient time to get
proper position in the crystal structure. Some crystalline solids are so small that appear to be amorphous.
But on examination under a powerful microscope it is also seen to have a definite crystalline shape. Such
solids are known as micro crystalline solide. Thus the crystallinity of a crystal may be defined as "a condition
of matter resulting from an or orderly, cohesive, three dimensional arrangement of its component particles
(atoms, ions or molecules) in space". This three dimensional arrangement is called crystal lattice or space
lattice. The position occupied by the particles in the crystal lattice are called lattice sites or lattice points. The
lattices are bound by surface that usually planar and known as faces of the crystal.
"The smallest geometrical position of the crystal which can be used as repetitive unit to build
up the whole crystal is called a unit cell."
Cooling curve of crystalline solid Cooling curve of an amorphous solid
Time Time
Temperature
Temperature
b
a
c
c indicate super cooled
liquid state
B
D
C A
Anisotropic behaviour of crystals
JEEMAIN.GURU
The angle between the two perpendiculars to the two intersecting faces is termed as the interfacial angle
which may be same as the angle between the unit cell edges. Goniometer is used to measure the interfacial
angle. It is important to note that interfacial angle of a substance remains the same although its shape may
be different due to conditions of formation.
                  
Interfacial angles of crystal
                 
This is known as law of constancy of interfacial angle or law of crystallography.
5 . TYPES OF THE CRYSTALS :
Crystal are divided into four important types on the basis of chemical bonding of the constituent atoms.
(i ) Ionic Crystals :
These are formed by a combination of highely electro-positive  
Cl
–
Na
+
Crystal structure of NaCl
ions (cations) and highly electronegative ions (anions). Thus
strong electrostatic force of attraction acts with in the ionic
crystals. Therefore, a large amount of energy is required to
separate ions from one another. The type of the crystal
lattice depends upon (i) The size of the ion (ii) The necessity
for the preservation of electrical neutrality. Therefore
alternate cations and anions in equivalent amounts are
arranged in the ionic crystal e.g. NaCl, KF, CsCl etc.
(i i) Covalent Crystals :
These are formed by sharing of valence electrons between two atoms resulting in the formation of a
covalent bond. The covalent bonds extend in two or three dimensions forming a giant interlocking
structure called network. Diamond and graphite are the good examples of this type.
(iii) Molecular Crystals :
In these crystals, molecules occupy the lattice points of the unit cells, except in solidified noble gases
in which the units are atoms, where the binding is due to vander Waal's' forces and dipole-dipole
forces. Since vander Waal's forces are non-directional hence structure of the crystal is determined by
geometric consideration only. Solid H
2
, N
2
, O
2
, CO
2
, I
2
, sugar etc. are well known examples of such
crystal in which vander Waal's forces are acting . Ice is the common example in which dipole-dipole
forces of attraction (hydrogen bonding) are active. Many organic and inorganic crystals involve hydrogen
bonds. Although these are comparatively weaker but play a very important role in determining the
structures of substances e.g. polynucleoides, proteins etc.
( i v) Metallic Crystals :
These are formed by a combination of atoms of electropositive elements. These atoms are binded by
metallic bonds. It may be defined as :
The force that binds a metal ion to a number of electrons within its sphere of influences is known as
metallic bond OR
A bond which is formed between electropositive elements OR
The attractive force which holds the atoms of two or more metals together in a metal crystal or in an
alloy.
JEEMAIN.GURU
Page 4


1 . INTRODUCTION :
Matter can exist in three physical states namely ; solid, liquid and gas. Matter consists of tiny particles
(atoms, ions or molecules). If the particles are very far off from one another, they behave like gases; nearer,
they behave like liquids, and nearest, like solids. The three states of matter are thus known as the three
states of aggregation from Latin word meaning "Flacking together".
The fundamental difference between the three states of aggregation lies essentially in the difference of the
relative amounts of energy possessed by the particles in the three states. The relative energies in the
different states of matter are governed by two universal opposing tendencies associated with the particles :
(i) They have tendency of mutual attraction.
(ii) They have tendency of escape from one another which is known as escaping tendency.
Whether a given system would exist as a solid, liquid or gas depends upon the relative strengths of these
opposing tendencies. If the escaping tendency is greater than the attraction between them, the molecules
will be carried far from each other to distances which are large as compared with their diameters, the system
will exists in gaseous state. But in the liquid state the molecular attraction exceeds the escaping tendency
and in the solid state the forces of attraction are so much greater than those of escaping tendency that each
particle is bound into a definite place in a rigid position by the mutual attraction of molecules. In other
words, in the solid state, the system possesses the amount of energy of motion i.e. kinetic energy.
2 . THE SOLID STATE :
The solid are characterised by incompressibility, rigidity and mechanical strength. The molecules, atoms or
ions in solids are closely packed i.e. they are held together by strong forces and can not move about at
random. Thus solids have definite volume, shape, slow diffusion, low vapour pressure and possesses the
unique property of being rigid. Such solids are known as true solids e.g. NaCl, KCl, Sugar, Ag, Cu etc. On
the other hand the solid which loses shapes on long standing, flows under its own weight and easily distorted
by even mild distortion forces are called pseudo solids e.g. glass, pitch etc.
Some solids such as NaCl, Sugar, Sulphur etc. have properties not only of rigidity and incompressibility but
also of having typical geometrical forms. These solids are called as crystalline solids. In such solids there is
definite arrangements of particles (atoms, ions or molecules) throughout the entire three dimensional network
of a crystal. This is named as long-range order. This three dimensional arrangement is called crystal
lattice or space lattice. Other solids such as glass, rubber, plastics etc. have rigidity and incompressibility
to a certain extent but they do not have definite geometrical forms or do not have long range order are
known as amorphous solids.
3 . DIFFERENCES BETWEEN CRYSTALLINE AND AMORPHOUS SOLIDS :
( i ) Characteristic Geometry : In the crystalline solids the particles (atoms, ions, or molecules) are
definitely and orderly arranged thus these have characteristic geometry while  amorphous solids do
not have characteristic geometry.
(i i) Melting Points : A crystalling solids has a sharp melting point i.e. it changes into liquid state at a
definite temperature. On the contrary an amorphous solid does not has a sharp melting point. For
example, when glass is heated,  it softens and then starts flowing without undergoing any abrupt or
sharp change from solid to liquid state. Therefore, amorphous solids are regarded as "liquids at all
temperatures".
(iii) Cooling curve : Amorphous solids show smooth cooling curve while crystalline solids show two
breaks in cooling curve. In the case of crystalline solids two breaks points 'a' and 'b' are appear. These
points indicate the beginning and the end of the process of crystallization. In this time interval temperature
remains constant. This is due to the fact that during crystallisation process energy is liberated which
compensates for the loss of heat thus the temperature remains constant.
THE SOLID STATE
JEEMAIN.GURU
( i v) Isotropy and Anisotropy : Amorphous solids differ from crystalline solids and resemble liquids in
many respects. The properties of amorphous solids, such as electrical conductivity, thermal conductivity,
mechanical strength, refractive index, coefficient of thermal expansion etc. are same in all directions.
Such solids are known as isotropic. Gases and liquids are also isotropic.
On the other hand crystalline solids show these physical properties different in diferent directions.
Therefore crystalline solids are called anisotropic. The anisotropy itself is a strong evidence for the
existence of orderly molecular arrangement in  crystals. For example, the velocity of light passing
through a crystal is different in different directions. A ray of light entering in a crystal may split up into
two components each following a different path and travelling with a different velocity.
This phenomenon is called double refraction. In the figure
two different kinds of atoms are shown in two dimensional
arrangement. If the properties are measured along the
direction CD, they will be different from those measured
along the direction AB. This is due to the fact that in the
direction AB each row is made up of one type of atoms
while in the direction CD each row is made up of two types
of atoms. It is important of note that in the case of
amorphous solids, liquids and gases atoms or molecules are
indentical and all properties are same in all directions.
( v ) Cutting :
Crystalline solids give clean cleavage while amorphous solids give irregular cut, due to conchoidal
fracture on cutting with a sharp edged tool.
4 . CRYSTALLINE STATE :
"A crystal is a solid composed of atoms (ions or molecules) arranged in an orderly repetitive array".
Most of the naturally occuring solids are found to have definite crystalline shapes which can be recognised
easily. These are in large size because these are formed very slowly thus particles get sufficient time to get
proper position in the crystal structure. Some crystalline solids are so small that appear to be amorphous.
But on examination under a powerful microscope it is also seen to have a definite crystalline shape. Such
solids are known as micro crystalline solide. Thus the crystallinity of a crystal may be defined as "a condition
of matter resulting from an or orderly, cohesive, three dimensional arrangement of its component particles
(atoms, ions or molecules) in space". This three dimensional arrangement is called crystal lattice or space
lattice. The position occupied by the particles in the crystal lattice are called lattice sites or lattice points. The
lattices are bound by surface that usually planar and known as faces of the crystal.
"The smallest geometrical position of the crystal which can be used as repetitive unit to build
up the whole crystal is called a unit cell."
Cooling curve of crystalline solid Cooling curve of an amorphous solid
Time Time
Temperature
Temperature
b
a
c
c indicate super cooled
liquid state
B
D
C A
Anisotropic behaviour of crystals
JEEMAIN.GURU
The angle between the two perpendiculars to the two intersecting faces is termed as the interfacial angle
which may be same as the angle between the unit cell edges. Goniometer is used to measure the interfacial
angle. It is important to note that interfacial angle of a substance remains the same although its shape may
be different due to conditions of formation.
                  
Interfacial angles of crystal
                 
This is known as law of constancy of interfacial angle or law of crystallography.
5 . TYPES OF THE CRYSTALS :
Crystal are divided into four important types on the basis of chemical bonding of the constituent atoms.
(i ) Ionic Crystals :
These are formed by a combination of highely electro-positive  
Cl
–
Na
+
Crystal structure of NaCl
ions (cations) and highly electronegative ions (anions). Thus
strong electrostatic force of attraction acts with in the ionic
crystals. Therefore, a large amount of energy is required to
separate ions from one another. The type of the crystal
lattice depends upon (i) The size of the ion (ii) The necessity
for the preservation of electrical neutrality. Therefore
alternate cations and anions in equivalent amounts are
arranged in the ionic crystal e.g. NaCl, KF, CsCl etc.
(i i) Covalent Crystals :
These are formed by sharing of valence electrons between two atoms resulting in the formation of a
covalent bond. The covalent bonds extend in two or three dimensions forming a giant interlocking
structure called network. Diamond and graphite are the good examples of this type.
(iii) Molecular Crystals :
In these crystals, molecules occupy the lattice points of the unit cells, except in solidified noble gases
in which the units are atoms, where the binding is due to vander Waal's' forces and dipole-dipole
forces. Since vander Waal's forces are non-directional hence structure of the crystal is determined by
geometric consideration only. Solid H
2
, N
2
, O
2
, CO
2
, I
2
, sugar etc. are well known examples of such
crystal in which vander Waal's forces are acting . Ice is the common example in which dipole-dipole
forces of attraction (hydrogen bonding) are active. Many organic and inorganic crystals involve hydrogen
bonds. Although these are comparatively weaker but play a very important role in determining the
structures of substances e.g. polynucleoides, proteins etc.
( i v) Metallic Crystals :
These are formed by a combination of atoms of electropositive elements. These atoms are binded by
metallic bonds. It may be defined as :
The force that binds a metal ion to a number of electrons within its sphere of influences is known as
metallic bond OR
A bond which is formed between electropositive elements OR
The attractive force which holds the atoms of two or more metals together in a metal crystal or in an
alloy.
JEEMAIN.GURU
We know that the force of attraction between metal ions and valency electrons is very strong. This force of
attraction is responsible for a compact solid structure of metal.
The important characteristics of the various types of crystals are given in the following table:
Some Important Characteristics of Various types of Crystals
Characteristics Ionic Crystals Covalent Mol ecul ar Metallic Crystals
 Crystals Crystals
 1. Units that Cations and  Atoms Molecules Positive ions in a
occupy lattice anions "sea or pond" of
points electrons.
 2. Binding Electrostatic Shared vander Waals Electrostatic
forces attraction electrons or Dipole- attraction between
between ions dipole positively charged
ions and negatively
charged electrons.
 3. Hardness Hard Very hard Soft Hard or soft
Graphite
is soft
 4. Brittleness Brittle Interme- Low Low
diate
 5. Melting point High Very high Low  Varying from
moderate to high
 6. Electrical Semi cond- Non-con- Bad condu- Good conductors
Conduction uctor due to ductor ctor
crystal impe- Graphite
rfections,con- is good
ductor in fused conductor
state
 7. Solubility in Soluble Insoluble Soluble as Good conductors
Polar solvents well as
insoluble
 8. Heat of NaCl(s) Graphite NH
3
(s) Cu(s)
Vaporisation 170-75 718-43 23.55 304.59
(kj mol
–1
)
 9. Heat of NaCl – NH
3
 (s) Cu(s)
fusion 28.45 – 5.65 13.016
(kj mol
–1
)
 10. Example NaCl, KNO
3
Diamond, H
2
O(s), Na, Cu, Ag, Fe,
CsCl, Na
2
SO
4
graphite, CO
2
(s), Pt, alloys
ZnS Quartz Sulphur,
(SiO
2
), Sugar,
SiC Iodine,noble
gases
JEEMAIN.GURU
Page 5


1 . INTRODUCTION :
Matter can exist in three physical states namely ; solid, liquid and gas. Matter consists of tiny particles
(atoms, ions or molecules). If the particles are very far off from one another, they behave like gases; nearer,
they behave like liquids, and nearest, like solids. The three states of matter are thus known as the three
states of aggregation from Latin word meaning "Flacking together".
The fundamental difference between the three states of aggregation lies essentially in the difference of the
relative amounts of energy possessed by the particles in the three states. The relative energies in the
different states of matter are governed by two universal opposing tendencies associated with the particles :
(i) They have tendency of mutual attraction.
(ii) They have tendency of escape from one another which is known as escaping tendency.
Whether a given system would exist as a solid, liquid or gas depends upon the relative strengths of these
opposing tendencies. If the escaping tendency is greater than the attraction between them, the molecules
will be carried far from each other to distances which are large as compared with their diameters, the system
will exists in gaseous state. But in the liquid state the molecular attraction exceeds the escaping tendency
and in the solid state the forces of attraction are so much greater than those of escaping tendency that each
particle is bound into a definite place in a rigid position by the mutual attraction of molecules. In other
words, in the solid state, the system possesses the amount of energy of motion i.e. kinetic energy.
2 . THE SOLID STATE :
The solid are characterised by incompressibility, rigidity and mechanical strength. The molecules, atoms or
ions in solids are closely packed i.e. they are held together by strong forces and can not move about at
random. Thus solids have definite volume, shape, slow diffusion, low vapour pressure and possesses the
unique property of being rigid. Such solids are known as true solids e.g. NaCl, KCl, Sugar, Ag, Cu etc. On
the other hand the solid which loses shapes on long standing, flows under its own weight and easily distorted
by even mild distortion forces are called pseudo solids e.g. glass, pitch etc.
Some solids such as NaCl, Sugar, Sulphur etc. have properties not only of rigidity and incompressibility but
also of having typical geometrical forms. These solids are called as crystalline solids. In such solids there is
definite arrangements of particles (atoms, ions or molecules) throughout the entire three dimensional network
of a crystal. This is named as long-range order. This three dimensional arrangement is called crystal
lattice or space lattice. Other solids such as glass, rubber, plastics etc. have rigidity and incompressibility
to a certain extent but they do not have definite geometrical forms or do not have long range order are
known as amorphous solids.
3 . DIFFERENCES BETWEEN CRYSTALLINE AND AMORPHOUS SOLIDS :
( i ) Characteristic Geometry : In the crystalline solids the particles (atoms, ions, or molecules) are
definitely and orderly arranged thus these have characteristic geometry while  amorphous solids do
not have characteristic geometry.
(i i) Melting Points : A crystalling solids has a sharp melting point i.e. it changes into liquid state at a
definite temperature. On the contrary an amorphous solid does not has a sharp melting point. For
example, when glass is heated,  it softens and then starts flowing without undergoing any abrupt or
sharp change from solid to liquid state. Therefore, amorphous solids are regarded as "liquids at all
temperatures".
(iii) Cooling curve : Amorphous solids show smooth cooling curve while crystalline solids show two
breaks in cooling curve. In the case of crystalline solids two breaks points 'a' and 'b' are appear. These
points indicate the beginning and the end of the process of crystallization. In this time interval temperature
remains constant. This is due to the fact that during crystallisation process energy is liberated which
compensates for the loss of heat thus the temperature remains constant.
THE SOLID STATE
JEEMAIN.GURU
( i v) Isotropy and Anisotropy : Amorphous solids differ from crystalline solids and resemble liquids in
many respects. The properties of amorphous solids, such as electrical conductivity, thermal conductivity,
mechanical strength, refractive index, coefficient of thermal expansion etc. are same in all directions.
Such solids are known as isotropic. Gases and liquids are also isotropic.
On the other hand crystalline solids show these physical properties different in diferent directions.
Therefore crystalline solids are called anisotropic. The anisotropy itself is a strong evidence for the
existence of orderly molecular arrangement in  crystals. For example, the velocity of light passing
through a crystal is different in different directions. A ray of light entering in a crystal may split up into
two components each following a different path and travelling with a different velocity.
This phenomenon is called double refraction. In the figure
two different kinds of atoms are shown in two dimensional
arrangement. If the properties are measured along the
direction CD, they will be different from those measured
along the direction AB. This is due to the fact that in the
direction AB each row is made up of one type of atoms
while in the direction CD each row is made up of two types
of atoms. It is important of note that in the case of
amorphous solids, liquids and gases atoms or molecules are
indentical and all properties are same in all directions.
( v ) Cutting :
Crystalline solids give clean cleavage while amorphous solids give irregular cut, due to conchoidal
fracture on cutting with a sharp edged tool.
4 . CRYSTALLINE STATE :
"A crystal is a solid composed of atoms (ions or molecules) arranged in an orderly repetitive array".
Most of the naturally occuring solids are found to have definite crystalline shapes which can be recognised
easily. These are in large size because these are formed very slowly thus particles get sufficient time to get
proper position in the crystal structure. Some crystalline solids are so small that appear to be amorphous.
But on examination under a powerful microscope it is also seen to have a definite crystalline shape. Such
solids are known as micro crystalline solide. Thus the crystallinity of a crystal may be defined as "a condition
of matter resulting from an or orderly, cohesive, three dimensional arrangement of its component particles
(atoms, ions or molecules) in space". This three dimensional arrangement is called crystal lattice or space
lattice. The position occupied by the particles in the crystal lattice are called lattice sites or lattice points. The
lattices are bound by surface that usually planar and known as faces of the crystal.
"The smallest geometrical position of the crystal which can be used as repetitive unit to build
up the whole crystal is called a unit cell."
Cooling curve of crystalline solid Cooling curve of an amorphous solid
Time Time
Temperature
Temperature
b
a
c
c indicate super cooled
liquid state
B
D
C A
Anisotropic behaviour of crystals
JEEMAIN.GURU
The angle between the two perpendiculars to the two intersecting faces is termed as the interfacial angle
which may be same as the angle between the unit cell edges. Goniometer is used to measure the interfacial
angle. It is important to note that interfacial angle of a substance remains the same although its shape may
be different due to conditions of formation.
                  
Interfacial angles of crystal
                 
This is known as law of constancy of interfacial angle or law of crystallography.
5 . TYPES OF THE CRYSTALS :
Crystal are divided into four important types on the basis of chemical bonding of the constituent atoms.
(i ) Ionic Crystals :
These are formed by a combination of highely electro-positive  
Cl
–
Na
+
Crystal structure of NaCl
ions (cations) and highly electronegative ions (anions). Thus
strong electrostatic force of attraction acts with in the ionic
crystals. Therefore, a large amount of energy is required to
separate ions from one another. The type of the crystal
lattice depends upon (i) The size of the ion (ii) The necessity
for the preservation of electrical neutrality. Therefore
alternate cations and anions in equivalent amounts are
arranged in the ionic crystal e.g. NaCl, KF, CsCl etc.
(i i) Covalent Crystals :
These are formed by sharing of valence electrons between two atoms resulting in the formation of a
covalent bond. The covalent bonds extend in two or three dimensions forming a giant interlocking
structure called network. Diamond and graphite are the good examples of this type.
(iii) Molecular Crystals :
In these crystals, molecules occupy the lattice points of the unit cells, except in solidified noble gases
in which the units are atoms, where the binding is due to vander Waal's' forces and dipole-dipole
forces. Since vander Waal's forces are non-directional hence structure of the crystal is determined by
geometric consideration only. Solid H
2
, N
2
, O
2
, CO
2
, I
2
, sugar etc. are well known examples of such
crystal in which vander Waal's forces are acting . Ice is the common example in which dipole-dipole
forces of attraction (hydrogen bonding) are active. Many organic and inorganic crystals involve hydrogen
bonds. Although these are comparatively weaker but play a very important role in determining the
structures of substances e.g. polynucleoides, proteins etc.
( i v) Metallic Crystals :
These are formed by a combination of atoms of electropositive elements. These atoms are binded by
metallic bonds. It may be defined as :
The force that binds a metal ion to a number of electrons within its sphere of influences is known as
metallic bond OR
A bond which is formed between electropositive elements OR
The attractive force which holds the atoms of two or more metals together in a metal crystal or in an
alloy.
JEEMAIN.GURU
We know that the force of attraction between metal ions and valency electrons is very strong. This force of
attraction is responsible for a compact solid structure of metal.
The important characteristics of the various types of crystals are given in the following table:
Some Important Characteristics of Various types of Crystals
Characteristics Ionic Crystals Covalent Mol ecul ar Metallic Crystals
 Crystals Crystals
 1. Units that Cations and  Atoms Molecules Positive ions in a
occupy lattice anions "sea or pond" of
points electrons.
 2. Binding Electrostatic Shared vander Waals Electrostatic
forces attraction electrons or Dipole- attraction between
between ions dipole positively charged
ions and negatively
charged electrons.
 3. Hardness Hard Very hard Soft Hard or soft
Graphite
is soft
 4. Brittleness Brittle Interme- Low Low
diate
 5. Melting point High Very high Low  Varying from
moderate to high
 6. Electrical Semi cond- Non-con- Bad condu- Good conductors
Conduction uctor due to ductor ctor
crystal impe- Graphite
rfections,con- is good
ductor in fused conductor
state
 7. Solubility in Soluble Insoluble Soluble as Good conductors
Polar solvents well as
insoluble
 8. Heat of NaCl(s) Graphite NH
3
(s) Cu(s)
Vaporisation 170-75 718-43 23.55 304.59
(kj mol
–1
)
 9. Heat of NaCl – NH
3
 (s) Cu(s)
fusion 28.45 – 5.65 13.016
(kj mol
–1
)
 10. Example NaCl, KNO
3
Diamond, H
2
O(s), Na, Cu, Ag, Fe,
CsCl, Na
2
SO
4
graphite, CO
2
(s), Pt, alloys
ZnS Quartz Sulphur,
(SiO
2
), Sugar,
SiC Iodine,noble
gases
JEEMAIN.GURU
6 . ISOMORPHISM : The occurence of a given substance in more than one solid crystalline forms have
different physical properties is known as polymorphism. This property when occurs in elements is known
as allotropy.
Sometimes we come across examples of chemically different solids which crystallise in the same crystalline
shape. Such substances are said to be Isomorphous (same shape). Their chemical constitutions are very
similar and in some cases crystals of one substance may continue to grow when placed in a saturated
solution of the other e.g. potash alum and chrome alum crystals have the same shape and can be grown in
each other's solutions. Mitscherlich deduced that isomorphous substances have similar chemical formula
e.g. phosphates and arsenates are said to be isomorphous with one another viz.
1. Na
2
HPO
4
.12H
2
O and Na
3
AsO
4
.12H
2
O
2. K
2
SO
4 
, K
2
CrO
4
3. ZnSO
4
.7H
2
O , MgSO
4
.7H
2
O , FeSO
4
.7H
2
O
4. KMnO
4
 , KClO
4
5. K
2
SO
4
.Al
2
(SO
4
)
3
.24H
2
O, K
2
SO
4
. Cr
2
(SO
4
)
3
.24H
2
O. However, the law is not without exceptions.
7 . SPACE LATTICE/CRYSTALLINE LATTICE/3–D LATTICE :
Space lattice is a regular arrangement of lattice points showing how the particles are arranged at different
sites in 3D–view.
Lattice
Point
 Lattice point Lines 
are used to represent
 geometry of crystal
" The three dimensional distribution of component particles in a crystal can be found by X-ray diffraction of
different faces of the crystal.
On the basis of the classification of symmetry, the crystals have been divided into seven systems. These can
be grouped into 32 classes which in turn can be regrouped into 7 crystal systems. These seven systems with
the characteristics of their axes (angles and intercepts) along with some examples of each are given in the
following table.
The Seven Crystal Systems
Name of Axes  Angles Bravais Lattices
 System
1 . Cubic a = b = c ? ?? ? ? ?? ? ???? ?? Primitive, Face-centred,
Body centred = 3
2 . Tetragonal a= b ? ?c ? ?? ? ? ?? ??? ?? ?? ? Primitive, Body centred = 2
3 . Rhombohedral a = b= c ? ?? ? ? ?? ? ??? ? ?? ?? Primitive = 1
or Trigonal
4 . Orthorhombic a ? ?b ? ? c ? ?? ? ? ?? ??? ?? ?? ? Primitive, Face-centred,
or Rhombic Body centred End centred = 4
5 . Monoclinic a ? ?b ? ?c ? ?? ? ???? ?? ?? Primitive, End - centred = 2
? ? ? ?90 ?
6 . Triclinic a ? ?b ? ?c ? ? ? ? ? ? ? ??? ? ? ?? ? Primitive = 1
7 . Hexagonal a = b ? ?c ? ? ?? ? ? ?? ?? ? Primitive = 1
?? ?? ?? ?? Total = 14
JEEMAIN.GURU
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