Title: States of matter
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2States of matter SESSION IV
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4Session objectives
- Vapour pressure of liquids
- Surface tension
- Viscosity
- Solids and their types
5Vapour 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
6Factors 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.
7Consequences of surface tension
Spherical shape of liquid drops
Capillary action
8Do 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.
9Viscosity
The internal resistance which one liquid layer
offers to another layer sliding over it, during
its flow is known as its viscosity.
10Viscosity
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
11What is solid ?
Solids have definite shape, definite volume and
strong force of attraction among constituting
particles.
12Crystalline and amorphous solids
13Ionic crystals
14Molecular crystals
15Covalent crystals
16Metallic crystals
17Lattice or space lattice or crystal lattice
18Unit cell
Is the smallest portion of the space lattice
which when repeated again and again in different
directionsgenerates the complete space lattice.
19Unit cell
20Bravais (1848)
Possible shapes of unit cell
21Arrangement of atoms/ ions in unit cell
- Primitive or Basic
- Body centered
- Face centered
- End centered
22Primitive 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
23Body 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
24Face 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
25End 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
26Co-ordination number
- Number of spheres which are touching a particle
sphere
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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28Illustrative 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
29Packing fraction
- Is the fraction of total volume of a cube
occupied by constituent particles.
30Packing fraction of simple cubic crystal
For simple cubic crystal(scc)
Packing fraction
For bcc, body diagonal, 4r
Packing fraction
A
B
a
31Packing fraction of face cubic crystal
For fcc, face diagonal, 4r
Packing fraction
C
a
A
B
32Density
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
33Density
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
34Density
Therefore, mass contained inone unit cell
Volume of unit cell (Edge length)3 a3
35Do you know
density depends on the type of the crystal
structure.
36X-ray reflection from crystals
37Class 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.
38Class 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.
39Class 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.
40Class 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)
41Class 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).
42Class 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).
43Class 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).
44Class exercise 8
Packing fraction of a scc unit cell is (a)
52 (b) 74 (c) 68 (d) 92
Solution
Hence, the answer is (a).
45Class 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.
46Class 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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