States of matter

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States of matter SESSION IV
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Session objectives

• Vapour pressure of liquids
• Surface tension
• Viscosity
• Solids and their types

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Vapour pressure of liquids
The pressure exerted by vapours in equilibrium
with liquid at a giventemperature.
Surface tension
the units of surface tension are Nm1 or J m2
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Factors affecting surface tension

• (i)Temperature
• Surface tension decreases with increase in
  temperature (because increase in temperature
  decreases the intermolecular forces.)
• (ii)Effect of surfactantsThe surface active
  agents decreases the surface tension of water
  

Surfactants

• For example, soap, detergent, ethanol.
• Addition of surfactants decreases the surface
  tension of liquid.

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Consequences of surface tension
Spherical shape of liquid drops
Capillary action
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Do you know?
How does water rises in a capillary?
The surface tension pulls the water into the
capillary .The surface tension of a fine
capillary is very largetherefore, it overcomes
the attraction of gravity on water.
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Viscosity
The internal resistance which one liquid layer
offers to another layer sliding over it, during
its flow is known as its viscosity.
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Viscosity
Where, f Force of friction between two layers
of liquid h Coefficient of viscosity a Area
of one layer of liquid in square centimetre x
Distance between the two layers of liquid. v
Difference in velocities of two layers of
liquid. Units of viscosity dynes cm2 s SI
units of viscosity Nm2 s
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What is solid ?
Solids have definite shape, definite volume and
strong force of attraction among constituting
particles.
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Crystalline and amorphous solids
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Ionic crystals
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Molecular crystals
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Covalent crystals
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Metallic crystals
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Lattice or space lattice or crystal lattice
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Unit cell
Is the smallest portion of the space lattice
which when repeated again and again in different
directionsgenerates the complete space lattice.
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Unit cell
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Bravais (1848)
Possible shapes of unit cell
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Arrangement of atoms/ ions in unit cell

• Primitive or Basic
• Body centered
• Face centered
• End centered

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Primitive cubic or simple cubic
Rank
Total no. of constituents per unit cell Total
number of corners x contribution by each atom
8 x 1/8 1
Simple or primitive
C
b
a
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Body centered cubic unit cell
Total no. of constituents per unit cell. Total
contribution of constituents at corners Total
contribution of particle at centre 8 x 1/8 1
x 1 1 1 2
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Face centered cubic unit cell
Total no. of constituents per unit cell. Total
contribution by constituents at corners Total
contribution by constituents on the faces 8 x
1/8 1/2 x 6 1 3 4
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End centered cubic unit cell
Total no. of constituents per unit cell. Total
contribution by constituents at corners Total
contribution by particles on the faces. 8 x 1/8
1/2 x 2 1 1 2
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Co-ordination number

• Number of spheres which are touching a particle
  sphere

• In ionic crystals

Number of oppositely charged ions surrounding a
particular ion e.g., Co-ordination number of Cl
and Na in NaCl molecule is 6each.
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Illustrative example
If three elements P,Q and R crystallizein a
cubic solid lattice with P atoms at the corners,
Q atoms at the cube centre and R atoms at the
centre of the faces of the cube, then write the
formula of the compound .
Solution
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Packing fraction

• Is the fraction of total volume of a cube
  occupied by constituent particles.

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Packing fraction of simple cubic crystal
For simple cubic crystal(scc)
Packing fraction
For bcc, body diagonal, 4r
Packing fraction
A
B
a
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Packing fraction of face cubic crystal
For fcc, face diagonal, 4r
Packing fraction
C
a
A
B
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Density
The number of particles present per unit cell.
Suppose the edge length of the unit cell
aNumber of atoms present in one unit cell
Z Atomic mass of the element M
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Density
Density of unit cell (r)
Mass contained in one unit cell Number of
particles in one unit cell Mass of one particle
Since mass of one particle
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Density
Therefore, mass contained inone unit cell
Volume of unit cell (Edge length)3 a3
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Do you know
density depends on the type of the crystal
structure.
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X-ray reflection from crystals
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Class exercise 1
Which of the following liquids is most difficult
to suck into pipette? (a) Toluene (b)
Water (c) Glycerol (d) Lemon juice
Solution-
Answer is (c).
Since it has highest viscosity.
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Class exercise 2
Which of the following is pseudo solid? (a)
Diamond (b) Common salt (c) Graphite (d)
Plastic
Solution
(d) Plastic is pseudo solid or amorphous solid.
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Class exercise 3
Which one of the following is not the property of
crystalline solid? (a) Isotropic (b) Sharp
melting point(c) Definite regular
geometry (d) High intermolecular forces
Solution
(a) Crystalline solids are an isotropic.
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Class exercise 4
With increase in temperature, the fluidity of
liquids (a) increases (b) remains
constant (c) Decreases (d) None of these
Solution
Hence, the answer is (a)
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Class exercise 5
The rise of liquid in a capillary tube is due
to (a) viscosity (b) effusion (c)
diffusion (d) surface tension
Solution
The liquid in capillary rises due to surface
tension.
Hence, the answer is (d).
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Class exercise 6
Which of the following statements is correct?(a)
Vapour pressure decreases with increase of
temperature (b) Vapour pressure increases with
increase of temperature (c) Vapour pressure is
independent of temperature (d) None of these
Solution
Hence, the answer is (b).
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Class exercise 7
Particles of quartz are packed by (a) van der
Waals forces (b) covalentely bonded
forces(c) electrical attraction forces (d)
None of these
Solution
Quartz is a covalent solid.
Hence, the answer is (b).
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Class exercise 8
Packing fraction of a scc unit cell is (a)
52 (b) 74 (c) 68 (d) 92
Solution
Hence, the answer is (a).
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Class exercise 9
Calculate the packing fraction of a fcc unit cell
if two face-centred atom have removed from the
unit cell.
Solution
For fcc, effective number of atom
Since two face-centred atoms have lost.
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Class exercise 10
Metallic gold crystallizes in fcc lattice with
edge length 4.07 Å. Find its density. (Au 197).
Solution
19.4 g/cm3
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