CHAPTER
ONE
The Solid State
TOPIC
1 General Characteristics
of Solid State
As we know, matter can exist in three states namely solid, liquid and gas. For different
applications, we need solids with widely different properties, which depend upon the
nature of constituent particles and the binding forces operating among them.
Solids differ from liquids, and gases in the fact that gases and liquids possess fluidity, i.e.
they can flow and hence called fluids, whereas solids do not possess fluidity, instead they
possess rigidity.
The fluidity in gases and liquids is due to the fact that the molecules are free to move
about, while rigidity in solids is due to the fixed positions of their constituent particles
which can only oscillate about their mean positions.
Therefore, under a given set of conditions of temperature and pressure, which of these
would be the most stable state of a given substance depends upon the net effect of two
opposing factors:
(i) Intermolecular forces which tend to keep the constituent particles closer.
(ii) Thermal energy which tends to keep them apart by making them move faster.
At sufficiently low temperature, thermal energy is low and intermolecular forces bring
molecules so close that they cling to one another and occupy fixed position and the
substance exists in solid state.
The solids possess following characteristic properties:
(i) Solids have definite mass, volume and shape.
(ii) They have strong intermolecular forces.
(iii) They are incompressible and rigid.
(iv) They have short intermolecular distances.
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Chapter Checklist
General Characteristics
of Solid State
Structure of Solids
Crystal Defects and
Properties of Solids
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(v) The constituent particles (atoms, molecules
or ions) have fixed position and can only
oscillate about their mean position.
Classification of Solids
Solids are classified into two categories on
the basis of the nature of order present in
arrangement of their constituent particles:
1. Crystalline Solids
A crystalline solid usually consists of a large
number of small crystals, each of them having a
definite characteristic geometrical shape.
In a crystal, the arrangement of constituent
particles is ordered. It has long range order which
means that there is a regular pattern of
arrangement of particles which repeats itself
periodically over the entire crystal. Sodium
chloride and quartz are typical examples of
crystalline solids.
Crystalline solids have a sharp melting point
that means they are true solids.
Nature
Crystalline solids are anisotropic in nature.
This arises from different arrangement of
particles in different directions. Since, the
arrangement of particles is different along
different directions, the value of same physical
property is found to be different along each
direction.
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Chemistry Class 12th
2. Amorphous Solids
The term amorphous is derived from the Greek word amorphos
which means ‘no form’.
An amorphous solid consists of particles of irregular shape. The
arrangement of constituent particles in such a solid has only short
range order. A regular and periodically repeating pattern is observed
over short distances only. Such portions are scattered and in between
the arrangement is disordered. Quartz glass, rubber and plastic are
typical examples of amorphous solids.
Amorphous solids soften over a range of temperature and can be
moulded and blown into various shapes. On heating, they become
crystalline at some temperature. That’s why a few glass objects from
ancient civilisations are found to become milky in appearance due to
crystallisation. Like liquids, amorphous solids have a tendency to flow
but very slowly. Therefore, they are called pseudo solids or
supercooled liquids. The tendency to flow in amorphous solids is
illustrated by the fact that the glass pans fixed to windows or doors of
old buildings are found slightly thicker at the bottom than at the top.
This is because the glass flows down very slowly and makes the
bottom portion slightly thicker.
Nature
Amorphous solids are isotropic in nature. It is because there is no
long range order in them and arrangement is irregular along all the
directions.
Isotropy It is the property due to which amorphous substances show
identical electrical and optical properties in all directions.
The structures of quartz (a crystalline) (Fig. a) and quartz glass
(Fig. b) (amorphous) are shown in fig. below,
B
D
C
A
Anisotropy in crystals is due to different
arrangement of particles along different directions
Anisotropy It is the property due to which
crystals show different electrical and optical
properties in different planes of the same
crystal.
(a)
(b)
The structure of amorphous solids is similar to that of liquids.
Due to difference in the arrangement of constituent particles, the two
types of solids differ in their properties.
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The Solid State
(b) Polar Molecular Solids
They consist of molecules having polar covalent bonds.
In these solids, molecules are held together by relatively
stronger dipole-dipole interactions. These solids are soft,
non-conductors of electricity and have comparatively higher
melting point than that of non- polar molecules. They exist
in gaseous or liquid state at room temperature, e.g. solid
SO 2 and solid NH3 .
Differences between crystalline and amorphous solids
Basis of
difference
Crystalline solids
Amorphous solids
Shape
They have definite
characteristic
geometrical shape.
They have irregular
shape.
Melting
point
They melt at a sharp
and characteristic
temperature.
They melt over a
range of temperature.
Cleavage
property
On cutting with sharp
edged tool, they split
into two pieces and
the newly generated
surfaces are plain
and smooth.
They give irregular
surfaces.
Nature
They are anisotropic
in nature and called
true solids.
They are isotropic in
nature and called
pseudo solids or
supercooled liquids.
Order in
arrangement
of
constituent
particles
They have long
range order.
They have short range
order.
Uses
Calcite crystal is
used in making
optical instrument
such as prism.
Amorphous silicon is
used as photovoltaic
material for
conversion of sunlight
into electricity.
Examples
Cu, Ag, Fe, S, etc.
Glass, rubber, plastic,
etc.
(c) Hydrogen Bonded Molecular Solids
They consist of molecules containing polar covalent
bonds between H and F, O or N atoms. Strong H-bonding
binds molecules of such solids (e.g. H 2O − ice). These solids
are volatile liquids or soft solids at room temperature and
pressure. They are also non-conductors of electricity.
Generally, they are volatile liquids or soft solids at room
temperature.
2. Ionic Solids
In these solids, constituent particles are ions. Cations
and anions are arranged in three-dimensional space. These
ions are held together by strong coulombic (electrostatic)
forces. These solids are hard, brittle and have high melting
and boiling points. In solid state, ionic solids are electrical
insulators because ions are not free to move. But in molten
state or in aqueous solution, they conduct electricity because
ions become free to move.
3. Metallic Solids
In these solids, constituent particles are positively
charged metal ions called Kernels and free electrons. These
electrons can easily flow throughout the metal crystal like
water in the sea. Hence, we call it a sea of free electrons.
Each metal atom contributes one or more electrons toward
this sea of mobile electrons. These free and mobile electrons
are responsible for high electrical and thermal conductivity
of metals.
Metal possesses lustre and colour in some cases. due to
the presence of free electrons in them.
Metals are highly malleable and ductile because of
unlike ionic crystals, the position of the positive ions can be
altered without destroying the crystal. Metals possess high
melting point due to the strong metallic bonds.
Classification of Crystalline Solids
Crystalline solids are classified (on the basis of nature
of intermolecular forces) into four categories:
1. Molecular Solids
In molecular solids, constituent particles are
molecules. These are again classified on the basis of type of
forces existing between the molecules.
(a) Non-polar Molecular Solids
Constituent particles are either atoms (noble gas–Ar,
He) or the molecules formed by non-polar covalent bonds
(H 2 , Cl 2 and I 2 ). In these solids, atoms or molecules are
held together by weak dispersion forces or London forces.
These solids are soft, non-conductors of electricity and
have low melting point and exist in gaseous or liquid state
at room temperature and pressure.
Metallic bond The force that holds the metal ions
together in the crystal, is called metallic bond.
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Chemistry Class 12th
4. Covalent or Network Solids
A wide variety of crystalline solids of non-metals result from the formation of covalent bonds between adjacent atoms
throughout the crystal. They are also called giant molecules.
Covalent bonds are strong and directional in nature, therefore atoms are held very strongly at their positions. These
solids are very hard, brittle and have extremely high melting points. They are insulators and do not conduct electricity,
e.g. diamond and silicon carbide.
Special Case of Covalent Solids : Graphite
Graphite is also a covalent solid but it is a soft solid and a good conductor of electricity. In graphite, carbon atoms are
arranged in different layers and each atom is covalently bonded to other three of its neighbouring atoms in the same layer.
The fourth valence electron is free in each carbon atom. These free electrons make graphite a good conductor of electricity.
In graphite, different layers can slide one over the other. For this reason, graphite is soft and acts as a good solid lubricant.
The structure of diamond and graphite is shown below:
340 pm
141.5 pm
Network structure
of diamond
Network structure of graphite
Different types of solids
Constituent
particles
Binding/attractive
forces
Physical
nature
(a) Non-polar
Molecules
Weak dispersion
or London forces
Soft
Very low
Insulator
He, Ar, Kr, H2 , Cl 2 ,
CH4 , I2 , CO 2 , CCl 4
(b) Polar
—
Dipole-dipole
interactions
Soft
Low
Insulator
HCl, SO 2
(c) Hydrogen
bonded
—
Hydrogen
bonding
Hard
Low
Insulator
H2O (ice)
lonic solids
Ions
Coulombic
(electrostatic)
forces of
attraction
Hard but
brittle
High
Insulators in solid
state but
conductors in
molten state and
in aqueous
solution
KCl, NaCl, CuSO 4 ,
CaF 2 , CsCl, ZnS,
MgO
Metallic solids
Positive ions in
a sea of mobile
electrons
Metallic bonding
Hard but
malleable and
ductile
Fairly high
Conductors in
solid state as well
as in molten state
Fe, Cu , Mg, Co,
Al, Au, Ag
Covalent or
network solids
Atoms
Covalent bonding
Very hard
except
graphite (soft)
Very high
Insulators except
graphite
SiO 2 (quartz), SiC,
C (diamond), AlN,
C (graphite)
Types of solids
Melting and
boiling point
Electrical
conductivity
Examples
Molecular solids
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Very Short Answer Type Questions
1. Why are solids rigid?
NCERT Intext
Sol. Because of strong attractive forces, particles have fixed
positions and they can only oscillate about their mean
position. So, solids are rigid.
8. Which types of solids have sharp melting points?
Sol. Crystalline solids have sharp melting points.
9. Which type of intermolecular force is present in ice?
Sol. H-bonding is present in ice.
2. Why do solids have a definite volume?
NCERT Intext
10. Why are amorphous solids called pseudo solids or
Sol. Strong attractive forces bind the solid particles and
thus they have fixed positions, so they cannot show
motion and possess definite volume.
supercooled liquids?
Sol. Amorphous solids have tendency to flow like liquids.
Hence, these are called pseudo solids or supercooled
liquids.
3. Why is glass considered a supercooled liquid?
NCERT Intext
11. What is the number of carbon atoms per unit cell
Sol. Glass is an amorphous solid. When heated it softens
and then starts flowing without changing state, thus it
is considered as a supercooled liquid.
HOTS
as well as in molten state and melts at extremely
high temperature. What type of solid is it?
NCERT Intext
12. Why are liquids and gases categorised as fluids?
Sol. SiO 2 (quartz), covalent (network) solid.
NCERT Exemplar
Sol. Liquids and gases have the tendency to flow that
means their molecules can move freely from one
place to another. Therefore, they are known as
fluids.
5. Ionic solids conduct electricity in molten state but
HOTS
not in solid state. Explain.
NCERT Intext
Sol. In ionic solids, the ions are not free to conduct
electricity. However, in molten state the ions
become free to move, so they conduct electricity.
13. Inspite of long range order in the arrangement of
particles, why are the crystals usually not perfect?
6. What types of solids are electric conductors,
malleable and ductile?
Sol. Metallic solids
of diamond unit cell?
Sol. The diamond lattice contains an fcc Bravais point
lattice which have two identical atoms per lattice
point. The diamond lattice contains 4 lattice
points per unit cell but contains 8 atoms per unit
cell.
4. Solid A is a very hard, electrical insulator in solid
HOTS
[1 Mark]
NCERT Exemplar
NCERT Intext
Sol. Crystals have long range repeated pattern of
arrangement of constituent particles but in the
process of crystallisation, some deviations from
the ideal arrangement (i.e. defects) may be
introduced. Therefore, crystals are usually not
perfect.
7. Which types of solids have definite enthalpy of
fusion?
Sol. Crystalline solids have definite enthalpy of fusion.
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Short Answer Type Questions
Chemistry Class 12th
[2 Marks]
1. Classify the following as amorphous or crystalline
solids,
NCERT Intext
Polyurethane, naphthalene, benzoic acid, teflon,
potassium nitrate, cellophane, polyvinyl chloride, fibre
glass, copper.
Sol. Crystalline solids Naphthalene, benzoic acid, potassium
nitrate, copper.
(1)
Amorphous solids Polyurethane, teflon, polyvinyl
chloride, fibre glass, cellophane.
(1)
6. Define the term ‘amorphous’. Give few
NCERT
examples of amorphous solids.
Sol. The term ‘amorphous’ is derived from Greek word
‘amorphos’ which means ‘no form’. In amorphous
solids, the constituent particles have a random
disordered arrangement. These are not true solids,
and are also called pseudo solids, e.g. glass, rubber,
(2)
plastics, etc.
7. Under which situation can an amorphous
2. Metallic solids are conductors of heat and electricity.
substance change to crystalline form ?
Why?
NCERT Exemplar
Sol. Metallic solids are collections of positive ions embedded in
a sea of electrons around it. These free electrons are
responsible for electric conduction in metallic solids. (2)
Sol. As a result of slow heating and cooling, over a
long period, an amorphous solid acquires some
crystalline character.
(2)
3. Graphite is a conductor of electricity. Give reasons.
8. Why are solids incompressible?
Sol. In graphite, three electrons of each carbon atom are bonded
to three other C atoms in covalent bonding. The fourth
valence electron of each atom forms a delocalised layer of
free electrons. These free electrons are responsible for the
conduction of electricity. That’s why, graphite is a
(2)
conductor of electricity.
4. Why glass panes fixed to windows or doors of
NCERT Exemplar
Sol. The distance between the constituent particles is
very less in solids. On bringing them still
closer repulsion will start between electron
clouds of these particles. Hence, they cannot be
brought further close together and are
(2)
incompressible.
old buildings are found to be thicker at the bottom?
9. What makes a glass different from a solid such
Sol. Glass panes fixed to windows or doors of buildings are
found to become thicker at the bottom because the glass
flows down slowly and makes the bottom portion thicker.
(2)
5. Some glass objects from ancient civilisations are found
to become milky in appearance. Explain.
Sol. Some glass objects from ancient civilisations are found to
become milky in appearance because of crystallisation of
glass.
(2)
Short Answer Type Questions
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as quartz? Under what conditions could quartz
NCERT
be converted into glass?
Sol. Glass is an example of amorphous solid in which
the constituent particles (SiO 4 , tetrahedral) have
only a short range order and there is no long range
order whereas in quartz, the constituent particles
(SiO 4 , tetrahedral) have short as well as long range
order. On melting and then cooling rapidly, it is
converted into glass.
(2)
[3 Marks]
1. Classify the following solids in different categories
based on the nature of intermolecular forces operating
in them:
Potassium sulphate, tin, benzene, urea, ammonia,
water, zinc sulphide, graphite, rubidium, argon, silicon
NCERT Intext
carbide.
Sol. Covalent solids Graphite, silicon carbide.
Molecular solids Benzene, ammonia, argon, urea, water.
Ionic solids Potassium sulphate, zinc sulphide.
Metallic solids Rubidium, tin.
(3)
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2. Refractive index of a solid is observed to have
the same value along all directions. Comment
on the nature of this solid. Would it show
NCERT Intext
cleavage property?
Sol. As solid has the same value of refractive index,
along all directions it is isotropic and thus
amorphous. Therefore, it would not show a clean
cleavage when cut with a knife, it would break
(3)
into pieces with irregular surfaces.
HOTS
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The Solid State
3. Classify each of the following solids as ionic, metallic, molecular, network (covalent) or
amorphous.
(i) Tetraphosphorus decaoxide (P4 O 10 )
(iii) SiC
(iv) I2
(vii) Brass
(viii) Rb
(xi) Plastics
Sol.
Ionic solids
(NH4 )3 PO 4 , LiBr
(ii) Ammonium phosphate (NH 4 ) 3 PO 4
(v) P4
(vi) Graphite
(ix) LiBr
(x) Si
NCERT
Metallic solids
Molecular solids
Network
Amorphous solids
(covalent) solids
Brass, Rb
P4O10 ,P4 , I2
Graphite, SiC, Si
Plastics
(3)
4. Explain
(i) the basis of similarities and differences between metallic and ionic crystals.
(ii) ionic solids are hard and brittle.
NCERT
Sol. (i) Similarities between ionic and metallic crystals
(a) Both ionic and metallic crystals have electrostatic forces of attraction. In ionic crystals, these
are between the oppositely charged ions. In metals, these are between kernels and valence
(1)
electrons. That is why both have high melting points.
(b) In both cases, the bond is non-directional.
Difference between ionic and metallic crystals
Basis of difference
Ionic crystals
Metallic crystals
Electrical
Conductivity
They conduct electricity in the molten state
or in aqueous solution but not in the solid
state. This is because in the solid state the
ions are not free to conduct electricity as
their positions are fixed.
In molten state or in aqueous solution, their
ions become mobile and hence, conduct
electricity.
They conduct electricity in the solid
state because in metals, the valence
electrons are free to flow.
Binding Forces
It is strong due to electrostatic forces of
attraction.
It may be weak or strong depending
upon the number of valence electrons
and the size of kernels.
Physical Nature
Ionic crystals are hard but brittle.
Metallic crystals are usually hard and
malleable.
(1)
(ii) Strong electrostatic forces of attraction among oppositely charged ions make ionic crystals hard
and since, the ionic bond is non-directional, they are brittle.
(1)
5. Stability of a crystal is reflected in the magnitude of its melting point, comment. Collect melting
HOTS
points of solid water, ethyl alcohol, diethyl ether and methane from data book. What can you
say about the intermolecular forces between these molecules?
NCERT
Sol. Higher the melting point, greater are the forces holding the constituent particles together and
hence greater is its stability.
(1)
The intermolecular forces in water and ethyl alcohol are mainly the hydrogen bonding but the
intermolecular H-bonding in water is stronger than in ethyl alcohol. Therefore, water has a higher
melting point than ethyl alcohol.
Diethyl ether is a polar molecule. The intermolecular forces present in them are dipole-dipole
attraction. Methane is a non-polar molecule. Therefore, the intermolecular forces operating in
them are the weak van der Waals’ forces (London dispersion forces).
(2)
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Value Based Questions
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Chemistry Class 12th
[4 Marks]
1. Manu went to the market to purchase a glass for
2. ‘‘Quartz is a crystalline solild whereas glass is
window pane. The shopkeeper had shown two types of
glasses one is transparent, and other is milky coloured
glass. A student of chemistry standing nearby advised
Manu to take the transparent glass.
(i) Why did the student advice Manu to buy the
transparent glass?
(ii) What phenomenon is associated with milkiness of
glass?
(iii) What values would you associate with the gesture of
the chemistry student?
Sol. (i) The transparent glass is stronger and more tempered
(2)
than milky glass.
(ii) The phenomenon associated with milkiness of glass is
the crystallisation of glass molecules.
(1)
(iii) The values that can be associated with the gesture of
the chemistry student is kindness and the will to share
knowledge with the underprivileged.
(1)
amorphous. It can be converted into glass and
used in photovoltaic cell.’’
(i) Why can quartz be used in a photovoltaic
cell?
(ii) Give, any one difference between quartz and
glass.
(iii) What values can be inferred from the nature
of the quartz depicted in the statement
above?
Sol. (i) Quartz has the properties to convert sunlight
into electric energy thus, it is used in
 1
photovoltaic cell.
1 
 2
(ii) Quartz is a crystalline solid whereas glass is
amorphous.
(1)
(iii) The values that we can infer from the nature of
quartz depicted by the given statement is that it
is versatile in nature, helpful in energy
 1
conservation and eco-friendly.
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 
 2
Long Answer Type Question
[5 Marks]
1. Give a differentiation between crystalline and amorphous solids with examples.
Sol. Refer to text on page 3.
(5)
Q.1
Why is glass of window panes of very old buildings found to be thicker at the bottom than at the top and why
is it milky ?
Q.2
Q.3
Why does urea have a sharp melting point but glass does not ?
Q.4
Q.5
Solid A is very hard, electrical insulator in solid state as well as in molten state and melts at extremely high
temperature. What type of solid is it ?
How do the structures of quartz and quartz glass differ from each other?
Diamond and solid rhombic sulphur both are covalent solids but the latter has very low melting point than the
former. Explain, why ?
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