In solids, molecules, ions or atoms are arranged in a definite pattern. Packing arrangement of particles is responsible for different types of solids and their properties

1. SOLIDS
X I F D C C H E M I S T R Y
S I D R A J AV E D

2. PACKING ARRANGMENT IN SOLIDS
• The structure of metals
can be explained when
atoms are packed
together.
• The atoms in metal are
considered as spheres
of identical size.

3. CLOSE PACKING OF PARTICLES
• The closest packing is the most efficient arrangement of spheres of
identical size and to fill available spaces in which each sphere touches
six neighbouring spheres.

4. Close Packing
Arrangements
Hexagonal Close
Packing HCP
Cubic Close
Packing CCP

5. CLOSE PACKING ARRANGEMENTS
• It can be explained by considering particles as spheres of
identical size arranged in row i.e. bottom layer A.
• When second layer of particles is placed on layer A, each
sphere of layer B will rest in the hollow void or hole in the
bottom layer.
• The spheres of the second layer will produce two types of
voids:
– A tetrahedral hole which falls above a sphere in the bottom layer
– An octahedral hole which falls above a void in the bottom layer

6. Tetrahedral void
Octahedral void

7. HCP AND CCP
• If tetrahedral holes are covered, the third layer is identical to
the bottom layer. This arrangement is called HCP arrangement
or ABAB or 1212 arrangement.
• If octahedral holes are covered, the third layer is not identical
with the bottom layer. This arrangement is called CCP
arrangement or ABCABC or 123123 arrangement.

10. Factors affecting
shapes of Ionic
Solids
Electrostatic forces
of attraction
Radius Ratio Conductivity

11. 1. ELECTROSTATIC
FORCES OF
ATTRACTION
The ionic solids are
composed of cations and
anions. They are held
together by strong
electrostatic forces of
attractions forming a well
defined geometric shape.
Formation of an ionic solid
is exothermic.
Na+ + Cl-  NaCl ∆H= -786 KJ/mol

12. 2. RADIUS RATIO
S.
No
Shape of ionic solid Radius Ratio
1 Body centred cubic 0.732 and
above
2 Octahedral 0.414 to 0.732
3 Tetrahedral 0.22 to 0.414
4 Triangular 0.15 to 0.22
The structure and shape of
an ionic solid depends
upon the radius ratio of
the cation and anions.
𝑅𝑎𝑑𝑖𝑢𝑠 𝑅𝑎𝑡𝑖𝑜
=
𝑅𝑎𝑑𝑖𝑢𝑠 𝑜𝑓 𝑐𝑎𝑡𝑖𝑜𝑛
𝑅𝑎𝑑𝑖𝑢𝑠 𝑜𝑓 𝑎𝑛𝑖𝑜𝑛

13. 3. P O O R CO NDUCTIVITY
The ionic crystals do not conduct
electricity in the solid state. The
shape of the crystals remains as
such. However when a solvent
(H2O) is added to the ionic solid
e.g. NaCl, crystal lattice is broken
and the ionic solid changes into
cation and anion. This is because
the crystal lattice is broken due
to high dielectric constant of
water. Thus the ions are said to
be solvated.
NaCl
𝐻2 𝑂
Na+ + Cl-

14. LATTICE ENERGY
• The amount of heat or energy released when gaseous ions of opposite
charges combine to give one mole of a crystalline ionic compound is
called lattice energy.
Na+ + Cl-  NaCl ∆H= -786 KJ/mol
• The amount of energy required to break one mole crystal lattice into its
gaseous ions is called lattice energy.
NaCl
𝐻2 𝑂
Na+ + Cl- ∆H= +786 KJ/mol
• Lattice energy depends upon size and charge of ions. It decreases with
the increase in the size of the ions and increases with increasing ionic
charges.

15. END OF LESSONs i d r a . j a v e d a l i @ g m a i l . c o m