SECOND YEAR HIGHER SECONDARY EXAMINATION
FOCUS AREA Notes of All Chapters in CHEMISTRY
1. THE SOLID STATE
Classification of solids
On the basis of orderly arrangement of particles, solids can be classified into two – Crystalline solids
and Amorphous solids
1. Crystalline solids:
Solids having long range order are called crystalline solids. Or, these are solids in which the particles
have a well ordered arrangement throughout the solid.
E.g.: Quartz, Diamond, Graphite, fullerene, NaCl, CuSO4.5H2O, ice, naphthalene, SiC etc.
in
2. Amorphous solids:
Solids having only short range order are called amorphous solids. Or, these are solids in which the
ordered arrangement of particles is only at some portions of the solid.
E.g.: Plastic, Glass (quartz glass), Rubber, amorphous silica, coal, charcoal, coke, PVC, Teflon etc.
Like liquids amorphous solids have a tendency to flow, though very slowly. Therefore, sometimes
.
these are also called pseudo solids or super cooled liquids.
Glass panes fixed to windows or doors of old buildings are slightly thicker at the bottom than at the
ve
top. This is because the glass flows down very slowly and makes the bottom portion slightly thicker.
Amorphous solids on heating become crystalline at some temperature. Some glass objects from
ancient civilizations are found to become milky in appearance due to some crystallization.
Differences between Crystalline solids and Amorphous solids
Properties Crystalline solids Amorphous solids
sli
Orderly Long range order Only short range order
arrangement of
particles
Geometrical shape Definite characteristic geometrical No definite Geometrical
shape shape
Hs
Melting point Definite m.p No definite m.p
Heat of fusion Definite Not definite
Mode of cleavage Give regular cleavage on cutting Give irregular cleavage on
cutting
Nature True solids Pseudo solids
Isotropy/anisotropy Anisotropic in nature Isotropic in nature
Anisotropic and isotropic substances
Solids in which the physical properties like electrical conductance, refractive index etc are different
when measured in different directions are said to be anisotropic in nature. This is due to the different
arrangement of particles in different directions. Crystalline solids are anisotropic.
Solids in which the physical properties are same along any direction are said to be isotropic in nature.
This is due to the irregular arrangement of particles along different directions. Amorphous solids are
isotropic.
+2 CHEMISTRY - Focus Area Notes Prepared by Anil Kumar K L, GHSS Ashtamudi, Kollam Page 1
,Crystal lattice
The regular three dimensional arrangements of constituent particles of a crystal in space is called
crystal lattice or space lattice.
Each point (atom, ion or molecule) in a lattice is called lattice point or lattice site. The significance of lattice
points is that when they are joined by straight lines, we get the geometry of the crystal.
There are only 14 possible three dimensional lattices. These are called Bravais Lattices.
Unit cell
A unit cell is the building block of a crystal. Or, it is the smallest portion of a crystal lattice which,
when repeated in three dimension to generate an entire lattice.
A unit cell is characterised by its edge lengths (a, b and c) and angle between the edges – α (between
b and c), β (between a and c) and γ (between a and b). Thus a unit cell is characterised by 6 parameters – a,
b, c, α, β and γ.
Classification of Unit cells
Unit cells are broadly divided into 2 based on the position of particles - primitive and centred unit cells.
in
1. Primitive Unit Cells:
Here the constituent particles are present only at the corners of the unit cell.
2. Centred Unit Cells:
Here the constituent particles are present at the corners and some other positions of the unit cell.
.
These are of three types:
i. Body-centred unit cells: particles are present at the body centre and at the corners of the
unit cell. ve
ii. Face-centred unit cells: particles are present at the centre of each faces and at the corners
of the unit cell.
iii. End-centred unit cells: particles are present at the centre of any two opposite faces and at
the corners of the unit cell.
Seven types of crystal systems and their possible variations
sli
Crystal Systems Possible Edge lengths Axial angles Examples
variations
Cubic Primitive, a=b=c α = β = γ = 900 NaCl, Zinc
body-centred, blende, Cu
face-centred
Tetragonal Primitive, a =b ≠ c α = β = γ = 900 White tin, TiO2,
Hs
body-centred SnO2, CaSO4
0
Orthorhombic Primitive, a≠b≠c α = β = γ = 90 Rhombic
body-centred, sulphur, KNO3,
face-centred, BaSO4
end-centred
Hexagonal Primitive a=b≠c α = β = 900, γ Graphite, ZnO,
=1200 CdS
0
Rhombohedral Primitive a=b=c α = β= γ ≠ 90 Calcite(CaCO3),
or trigonal HgS (Cinnabar)
Monoclinic Primitive, a≠b≠c α = γ = 900, Monoclinic
end-centred β ≠ 900 sulphur,
Na2SO4.10H2O
Triclinic Primitive a≠b≠c α ≠ β ≠ γ ≠ 900 K2Cr2O7, H3BO3,
CuSO4.5H2O
+2 CHEMISTRY - Focus Area Notes Prepared by Anil Kumar K L, GHSS Ashtamudi, Kollam Page 2
,Calculation of Number of atoms in a unit cell (z)
Primitive cubic (Simple Cubic) unit cell:
Here atoms are present only at the corners of the cube. Each corner atom is shared by 8 unit cells.
Therefore, contribution to one unit cell = 1/8
Since each unit cell has 8 atoms at the corners, total number of atoms in one unit cell = 8×1/8 = 1
So for a primitive (simple cubic) unit cell, z = 1
Body-centred cubic (bcc) unit cell:
Here the particles are present at the corners of the cube and also one atom at the body centre.
The number of atoms at the corner = 8×1/8 = 1
The atom present at the centre of the body is not shared by other atoms.
So the number of atoms at the body-centre = 1
Therefore, total number of atoms in the unit cell = 1+1=2
So, for a bcc, z = 2
in
Face-centred cubic (fcc) unit cell:
Here the atoms are present at the corners and also at the centre of each faces. Each corner atom is
shared by 8 unit cells and each face centre atom is shared by 2 unit cells.
Number of corner atoms = 8×1/8 = 1
.
Number of face-centre atoms = 6×1/2 = 3
Therefore, total number of atoms = 1+3 = 4
So, for an fcc, z = 4
Close packing in solids
ve
Solids are three dimensional and the 3 D structure can be obtained by the following three steps:
1. Close packing in One Dimensions
Here the spheres (particles) are arranged in a row touching each other. In this arrangement each sphere
is in contact with 2 adjacent spheres. Therefore, co-ordination number of each sphere is 2.
sli
2. Close packing in Two Dimensions
Here the spheres are arranged in two directions – length-wise and breadth-wise. This can be done in two
different ways.
i. Square close packing in two dimensions: Here each sphere is in contact with four adjacent spheres.
So the co-ordination number of each sphere is 4.
ii. Hexagonal close packing in two dimensions: Here each sphere is in contact with six adjacent
Hs
spheres. So the co-ordination number of each sphere is 6.
Square close packing Hexagonal close packing
+2 CHEMISTRY - Focus Area Notes Prepared by Anil Kumar K L, GHSS Ashtamudi, Kollam Page 3
, In 2D close packing, hexagonal close packing is more efficient since the maximum space is occupied by
spheres.
3. Three Dimensional close packing
Here the particles are arranged in layers. This can be possible in two ways.
i. Three dimensional close packing from two dimensional square close-packed layers:
Here the spheres of the each layer are placed exactly above those of the lower layer. In this
arrangement, all the layers are identical. So if we call the first layer as A, then all the layers are of ‘A’
type. So this arrangement forms AAA….. type pattern. The lattice thus generated is the simple cubic
lattice and its unit cell is the primitive cubic unit cell.
ii. Three dimensional close packing from two dimensional hexagonal close-packed layers:
Here the first layer is arranged as hexagonal manner. The second layer is placed above the
depressions of the first layer. On placing the second layer there arises two types of voids (vacant spaces)
in
above the second layer – tetrahedral voids and octahedral voids. Thus when we place the third layer
over the second there are two possibilities:
Covering tetrahedral voids: Here the spheres of the third layer are placed above the
tetrahedral voids of the second layer. In this arrangement, the spheres of the 3rd layer are vertically
above those of the 1st layer. Similarly the 4th layer is a repetition of the 1st layer. This will form the
.
pattern ABAB…… This type of close packing is called Hexagonal close packing (hcp) in three dimensions.
ve
This type of arrangement is found in metals like Mg, Zn etc.
Covering octahedral voids: Here the spheres of the third layer are placed above the
octahedral voids of the second layer. In this arrangement, the 1st, 2nd nad 3rd layers are different. But
the 4th layer is identical to the 1st layer, the 5th layer to the 2nd layer and so on. This will form the
pattern ABCABC…… This type of close packing is called cubic close packing (ccp) or face-centred
cubic(fcc) packing in three dimensions. This type of arrangement is found in metals like Cu, Ag etc.
sli
Hs
Both hcp and ccp are equally efficient since 74% of the available space is occupied by spheres.
Co-ordination Number
In a close packed arrangement the number of nearest neighbours with which a given sphere is in
contact is called the co-ordination number of that sphere. In both hcp and ccp, co-ordination number in both
hcp and ccp is 12.
Interstitial voids
The vacant space in close packed arrangement is called voids. These are of two types- tetrahedral
voids and octahedral voids.
+2 CHEMISTRY - Focus Area Notes Prepared by Anil Kumar K L, GHSS Ashtamudi, Kollam Page 4
FOCUS AREA Notes of All Chapters in CHEMISTRY
1. THE SOLID STATE
Classification of solids
On the basis of orderly arrangement of particles, solids can be classified into two – Crystalline solids
and Amorphous solids
1. Crystalline solids:
Solids having long range order are called crystalline solids. Or, these are solids in which the particles
have a well ordered arrangement throughout the solid.
E.g.: Quartz, Diamond, Graphite, fullerene, NaCl, CuSO4.5H2O, ice, naphthalene, SiC etc.
in
2. Amorphous solids:
Solids having only short range order are called amorphous solids. Or, these are solids in which the
ordered arrangement of particles is only at some portions of the solid.
E.g.: Plastic, Glass (quartz glass), Rubber, amorphous silica, coal, charcoal, coke, PVC, Teflon etc.
Like liquids amorphous solids have a tendency to flow, though very slowly. Therefore, sometimes
.
these are also called pseudo solids or super cooled liquids.
Glass panes fixed to windows or doors of old buildings are slightly thicker at the bottom than at the
ve
top. This is because the glass flows down very slowly and makes the bottom portion slightly thicker.
Amorphous solids on heating become crystalline at some temperature. Some glass objects from
ancient civilizations are found to become milky in appearance due to some crystallization.
Differences between Crystalline solids and Amorphous solids
Properties Crystalline solids Amorphous solids
sli
Orderly Long range order Only short range order
arrangement of
particles
Geometrical shape Definite characteristic geometrical No definite Geometrical
shape shape
Hs
Melting point Definite m.p No definite m.p
Heat of fusion Definite Not definite
Mode of cleavage Give regular cleavage on cutting Give irregular cleavage on
cutting
Nature True solids Pseudo solids
Isotropy/anisotropy Anisotropic in nature Isotropic in nature
Anisotropic and isotropic substances
Solids in which the physical properties like electrical conductance, refractive index etc are different
when measured in different directions are said to be anisotropic in nature. This is due to the different
arrangement of particles in different directions. Crystalline solids are anisotropic.
Solids in which the physical properties are same along any direction are said to be isotropic in nature.
This is due to the irregular arrangement of particles along different directions. Amorphous solids are
isotropic.
+2 CHEMISTRY - Focus Area Notes Prepared by Anil Kumar K L, GHSS Ashtamudi, Kollam Page 1
,Crystal lattice
The regular three dimensional arrangements of constituent particles of a crystal in space is called
crystal lattice or space lattice.
Each point (atom, ion or molecule) in a lattice is called lattice point or lattice site. The significance of lattice
points is that when they are joined by straight lines, we get the geometry of the crystal.
There are only 14 possible three dimensional lattices. These are called Bravais Lattices.
Unit cell
A unit cell is the building block of a crystal. Or, it is the smallest portion of a crystal lattice which,
when repeated in three dimension to generate an entire lattice.
A unit cell is characterised by its edge lengths (a, b and c) and angle between the edges – α (between
b and c), β (between a and c) and γ (between a and b). Thus a unit cell is characterised by 6 parameters – a,
b, c, α, β and γ.
Classification of Unit cells
Unit cells are broadly divided into 2 based on the position of particles - primitive and centred unit cells.
in
1. Primitive Unit Cells:
Here the constituent particles are present only at the corners of the unit cell.
2. Centred Unit Cells:
Here the constituent particles are present at the corners and some other positions of the unit cell.
.
These are of three types:
i. Body-centred unit cells: particles are present at the body centre and at the corners of the
unit cell. ve
ii. Face-centred unit cells: particles are present at the centre of each faces and at the corners
of the unit cell.
iii. End-centred unit cells: particles are present at the centre of any two opposite faces and at
the corners of the unit cell.
Seven types of crystal systems and their possible variations
sli
Crystal Systems Possible Edge lengths Axial angles Examples
variations
Cubic Primitive, a=b=c α = β = γ = 900 NaCl, Zinc
body-centred, blende, Cu
face-centred
Tetragonal Primitive, a =b ≠ c α = β = γ = 900 White tin, TiO2,
Hs
body-centred SnO2, CaSO4
0
Orthorhombic Primitive, a≠b≠c α = β = γ = 90 Rhombic
body-centred, sulphur, KNO3,
face-centred, BaSO4
end-centred
Hexagonal Primitive a=b≠c α = β = 900, γ Graphite, ZnO,
=1200 CdS
0
Rhombohedral Primitive a=b=c α = β= γ ≠ 90 Calcite(CaCO3),
or trigonal HgS (Cinnabar)
Monoclinic Primitive, a≠b≠c α = γ = 900, Monoclinic
end-centred β ≠ 900 sulphur,
Na2SO4.10H2O
Triclinic Primitive a≠b≠c α ≠ β ≠ γ ≠ 900 K2Cr2O7, H3BO3,
CuSO4.5H2O
+2 CHEMISTRY - Focus Area Notes Prepared by Anil Kumar K L, GHSS Ashtamudi, Kollam Page 2
,Calculation of Number of atoms in a unit cell (z)
Primitive cubic (Simple Cubic) unit cell:
Here atoms are present only at the corners of the cube. Each corner atom is shared by 8 unit cells.
Therefore, contribution to one unit cell = 1/8
Since each unit cell has 8 atoms at the corners, total number of atoms in one unit cell = 8×1/8 = 1
So for a primitive (simple cubic) unit cell, z = 1
Body-centred cubic (bcc) unit cell:
Here the particles are present at the corners of the cube and also one atom at the body centre.
The number of atoms at the corner = 8×1/8 = 1
The atom present at the centre of the body is not shared by other atoms.
So the number of atoms at the body-centre = 1
Therefore, total number of atoms in the unit cell = 1+1=2
So, for a bcc, z = 2
in
Face-centred cubic (fcc) unit cell:
Here the atoms are present at the corners and also at the centre of each faces. Each corner atom is
shared by 8 unit cells and each face centre atom is shared by 2 unit cells.
Number of corner atoms = 8×1/8 = 1
.
Number of face-centre atoms = 6×1/2 = 3
Therefore, total number of atoms = 1+3 = 4
So, for an fcc, z = 4
Close packing in solids
ve
Solids are three dimensional and the 3 D structure can be obtained by the following three steps:
1. Close packing in One Dimensions
Here the spheres (particles) are arranged in a row touching each other. In this arrangement each sphere
is in contact with 2 adjacent spheres. Therefore, co-ordination number of each sphere is 2.
sli
2. Close packing in Two Dimensions
Here the spheres are arranged in two directions – length-wise and breadth-wise. This can be done in two
different ways.
i. Square close packing in two dimensions: Here each sphere is in contact with four adjacent spheres.
So the co-ordination number of each sphere is 4.
ii. Hexagonal close packing in two dimensions: Here each sphere is in contact with six adjacent
Hs
spheres. So the co-ordination number of each sphere is 6.
Square close packing Hexagonal close packing
+2 CHEMISTRY - Focus Area Notes Prepared by Anil Kumar K L, GHSS Ashtamudi, Kollam Page 3
, In 2D close packing, hexagonal close packing is more efficient since the maximum space is occupied by
spheres.
3. Three Dimensional close packing
Here the particles are arranged in layers. This can be possible in two ways.
i. Three dimensional close packing from two dimensional square close-packed layers:
Here the spheres of the each layer are placed exactly above those of the lower layer. In this
arrangement, all the layers are identical. So if we call the first layer as A, then all the layers are of ‘A’
type. So this arrangement forms AAA….. type pattern. The lattice thus generated is the simple cubic
lattice and its unit cell is the primitive cubic unit cell.
ii. Three dimensional close packing from two dimensional hexagonal close-packed layers:
Here the first layer is arranged as hexagonal manner. The second layer is placed above the
depressions of the first layer. On placing the second layer there arises two types of voids (vacant spaces)
in
above the second layer – tetrahedral voids and octahedral voids. Thus when we place the third layer
over the second there are two possibilities:
Covering tetrahedral voids: Here the spheres of the third layer are placed above the
tetrahedral voids of the second layer. In this arrangement, the spheres of the 3rd layer are vertically
above those of the 1st layer. Similarly the 4th layer is a repetition of the 1st layer. This will form the
.
pattern ABAB…… This type of close packing is called Hexagonal close packing (hcp) in three dimensions.
ve
This type of arrangement is found in metals like Mg, Zn etc.
Covering octahedral voids: Here the spheres of the third layer are placed above the
octahedral voids of the second layer. In this arrangement, the 1st, 2nd nad 3rd layers are different. But
the 4th layer is identical to the 1st layer, the 5th layer to the 2nd layer and so on. This will form the
pattern ABCABC…… This type of close packing is called cubic close packing (ccp) or face-centred
cubic(fcc) packing in three dimensions. This type of arrangement is found in metals like Cu, Ag etc.
sli
Hs
Both hcp and ccp are equally efficient since 74% of the available space is occupied by spheres.
Co-ordination Number
In a close packed arrangement the number of nearest neighbours with which a given sphere is in
contact is called the co-ordination number of that sphere. In both hcp and ccp, co-ordination number in both
hcp and ccp is 12.
Interstitial voids
The vacant space in close packed arrangement is called voids. These are of two types- tetrahedral
voids and octahedral voids.
+2 CHEMISTRY - Focus Area Notes Prepared by Anil Kumar K L, GHSS Ashtamudi, Kollam Page 4
