Solids can be classified as Ionic solids, covalent network solids, metallic solids and molecular solids.

1. SOLIDS
XI FDC CHEMISTRY
SIDRA JAVED

2. IONIC SOLIDS
An ionic crystal is formed
due to the transference of
electrons from one atom
to the other.
The Cations and Anions
formed are held together
through strong
electrostatic forces.

3. Formation of NaCl
Sodium loses one electron to be
converted into Na+ ion
Na  Na+ + 1e-
Chlorine gains one electron to
be converted into Cl- ion
Cl + 1e-  Cl-
These ions combine together
due to strong electrostatic
attraction forces
Na+ + Cl-  NaCl ∆H = -786 KJ/mol

4. Crystal lattic of NaCl

5. Covalent network solids
The crystalline solids in which atoms of similar or
dissimilar elements are held together in a network of
single bond are known as covalent crystals or covalent
network solids.

6. Formation of Covalent crystals
i. When covalent bonds give
giant molecules.
ii. When atoms join together by
covalent bonds and as a result
separate layers are formed.

7. Comparison between Ionic and
Covalent Solids
Ionic Solids
1. Ionic solids are non
conductors of electricity in
their solid state. However
they conduct electricity in
the molten or solution form.
2. Ionic solids have definite
geometric shape.
3. They are non-directional in
nature.
4. They do not exist in
molecules due to their ionic
nature.
Covalent network solids
1. They are bad conductors of
electricity with the exception of
graphite.
2. They have definite shape and
oriented in 3D with network
structure.
3. They have open structures due
to valences of atoms directed
in definite directions.
4. They may be called as
molecules due to their covalent
nature.

8. Low density of ice
When the temperature is
decreased the molecules come
close to each other. As a result
the intermolecular attractive
forces increase.
However some empty spaces are
developed in the ice. As a result
about 9% more spaces than
liquid water are produced.
As the density is inversely
proportional to volume, the
increase in volume decreases the
density. That is why ice floats
over water.

9. Applications of low density of
ice in real life
In cold countries when the
temperature is decreased to
0oC, water in ponds and
lakes freezes. A thick layer
of ice is formed that stays at
the top. This layer of ice acts
as insulator for further heat
loss. Fish and plants can
survive in the water for
months under the thick
blanket of ice.

10. High heat of fusion of ice
The quantity of heat required to convert one mole of a
solid into liquid is called molar heat of fusion.
Molar heat of fusion for ice is +6.02 KJ/mol
Ice (solid)  Water (liquid) ∆H = 6.02 KJ/mol

11. Application of high heat of
fusion of ice in daily life
Ice absorbs 0.333 KJ of energy for every
gram of ice to melt.To melt 100 gram of
ice, 33.3 KJ of energy is required.
It means if 33.3 KJ of energy from the
surrounding is absorbed by each of the
drink, the temperature of the drink without
ice would rise from 0oC to 20oC.
The drink containing the ice would remain
at 0oC but 100 gram of ice would melt.

12. Hygroscopic salts
Some salts absorbs moisture from atmosphere. Such salts
are called hygroscopic salts.
CaCl2 has the ability to absorb moisture from atmosphere.
Thus it becomes hygroscopic.
The absorption of moisture becomes maximum when there is
humidity in air. The water molecules absorbed will become
part of crystal of CaCl2 and may be called as water of
crystallization.
A salt containing water of crystallization is called hydrate.
CaCl2 can absorb a maximum of 2 water molecules there fore
it becomes CaCl2.2H2O.
The water of crystallization increase the mass of CaCl2.

13. How to get NaCl from saline
solution?
Saline water (NaCl solution) contains water along wih
certain impurities.
If saline water is allowed to freeze in freezing mixture,
the impurities come up to the surface in the form of ice
at -3.4oC leaving behind NaCl.
Ice and impurities are removed from the surface leaving
behind pure NaCl.

14. End of lesson
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