Solid state part 3 | Chemistry Class 12 | By Mrs. Shubhada Walawalkar

UNIT: 1
SOLID STATE
Part-III
1.4 Crystal Structure
Marks 4-6
Sou S.S.Walawalkar - N.S.P.Jr.college.Devgad

1.4.1 Crystal, lattice and basis
Lattice +Basis = Crystal
What is lattice?
Regular and periodic three dimensional geometric arrangement of
points in space. It is used to describe structure of crystal.
Two dimensional lattice.

What is Basis?
Set of atoms associated with each lattice point.
Crystal = lattice + basis

1.4.2 Unit Cell
- Unit cell is smallest repeating structural unit of
crystalline solid

➢ When unit cells are
stacked together to
generate crystal each
unit cell share its faces
edges and corners with
neighboring unit cell.
➢ a, b, c are the
dimensions of unit cell.
➢ α β γ are the angles
between these axes
Unit cell Unit cell

Unit
cell
1) Primitive or simple unit cell
Constituent particles are present at its corners
2) Body centered unit cell
One constituent particles is present at the center of its
body
in addition to the corner particles
3) Face centered unit cell
constituent particles are present at the center of each faces
in addition to the corner particlesFace centered unit cell
4)Base centered unit cell
Constituent particles are present at the centers of any two its
opposite faces
in addition to the corner particles

1.4.3Types of unit cell
1) Primitive or simple unit cell-
✓ constituent particles are present at its corners only.

2) Body centered unit cell
✓ One constituent particle
is present at the center of
its body in addition to the
corner particles.
3) Face centered unit cell
✓ Consists of particles at
the center of each of the
faces in addition to the
corner particles.
4) Base centered unit cell
✓ Consist of particles at the
center of any two of its
opposite faces in addition
to corner particles.

1.4.4 Crystal system
✓ 14 different kind of space lattices are possible which describe the
crystal structure ,are called Bravais lattice.

14 Bravais
lattice
1) Cubic
2) Tetragonal
3) Orthorhombic
4) Rhombohedral
5) Monoclinic
6) Triclinic
7) Hexagonal
Bravais lattice are
divided in to 7 crystal
systems.

Cubic
system
Simple cubic
Particles are at the 8 corners of cube.
Body centered cubic
particles at its 8 corners & an additional particle
in the center of the cube.
Face centered cubic
particles at its 8 corners & at the center of each of six
faces of the cube .
1.5 Cubic system

1) Simple
Cubic((SC)
. Has 8 corners
1/8 × 8 =1
particle per
unit cell.
2)Body
Centered
Cubic(BCC)H
as 8 corners
1/8 × 8 =1
1 particle at the
center.
1+ 1 = 2
particles per unit
cell
3)Face
Centered
Cubic (FCC)
Has 8 corners
1/8 × 8 =1 .
Has 6 faces.
1/2 × 6 = 3
1+3 = 4
particles per unit
cell
1.5.1 Cubic system :-3 types of cubic cells

Tetragonal system Monoclinic system

Important points
1) Each corner particle of a cube is shared by 8
cubes.
2) Each face particle is shared by 2 cubes.
3) Each edge particle is shared by 4 cubes.

1.5.2 Relationship between molar mass, density
of the substance and unit cell edge length, is
deduced in the following steps
1)If edge length of cubic unit cell is a, the
volume of unit cell is a3
2) Suppose that mass of one particle is m
and that there are n particles per unit cell.
•Mass of unit cell = m × n ……..(1.1)

3) The density of unit cell (ρ), which is same as
density of the sub-substance is given by
ρ = mass of unit cell
Volume of unit cell
= m× n
a3
= density of substance……..(1.2)

4) Molar mass (M) of the substance is given by
M = mass of one particle × number of particles per mole
= m × NA
Therefore, m= M/NA……………(1.3)
5) Combining Eq. (1.1) and (1.3), gives
ρ = n M/ a3NA…………(1.4)
By knowing any four parameters of Eq. (1.4),
the fifth can be calculated.
(NA is Avogadro number)

THANK YOU!

Solid state part 3 | Chemistry Class 12 | By Mrs. Shubhada Walawalkar

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Solid state part 3 | Chemistry Class 12 | By Mrs. Shubhada Walawalkar