5. Solids which have no definite geometrical
shape and no sharp melting point are
called amorphous solid.
6. Amorphous solids are
1. Not Shining in light
2. Particles are not arranged
in regular order.
3. Isotropic.
7. Difference between
Crystalline solids Amorphous solid
1 Have definite geometrical shape 1 Have no definite geometrical shape
2 Shine in light 2 Do not Shine in light
3 Anisotropic 3 Isotropic
4 Have Sharp melting Point 4 Have no Sharp melting Point
5 Have definite heat of fusion. 5 Have no definite heat of fusion.
9. Types of Crystalline Solids
1. Ionic crystals are crystals containing ions in the lattice
point
Eg : Na+ Cl- CsCl, MgCl2 Etc
10. 2. Molecular crystals are crystals containing molecules
in the lattice point
Eg : Ice, Dry ice, solid ammonia Etc
11. 3. Covalent crystals are crystals containing covalently
bonded atoms in the lattice point
Eg : Diamond, Carborundam, graphite and Qurtz
12. 4. Metallic crystals are crystals containing definite
geometrical arrangement of metal atoms in the lattice point
Eg : Cu, Zn, Li, Fe Etc.
13. Crystal Lattice
Crystal lattice or space lattice indicates 3-D arrangements of
atoms/ ions/ molecule present in the crystal.
Lattice points are the positions of
atoms/ions/molecules that forms crystal
lattice. When lattice points are joined by
straight line, it results in a definite
geometrical shape of the crystal.
14. Unit Cell:
The unit cell is the smallest portion of the crystal lattice having the
shape of the crystal which can repeat in three dimentions to form
entire crystal structure.
TYPES OF CUBIC UNIT CELL
16. Coordination Number (C.N)
Coordination number of a particle in a crystal is the
number of its nearest neighbouring particles in a
crystal.
C.N=6 C.N=8 C.N=12
17. TYPE OF CUBIC LATTICE
Simple cube
The unit cell has eight lattice points at the
eight corners of the cube. It also known as
primitive or basic unit cell
Coordination Number =8
18. Body centred cube
The unit cell has nine lattice points at the
eight corners of the cube and one at the
centre of the body.
Coordination Number=8
19. Face centred cube
The unit cell has 14 lattice points at the eight
corners of the cube and six at the centres of
the faces.
Coordination Number=12
20. Calculation of number of particles present in cubic unit
cells:
The particles present in crystal lattice are
shared between severel units. So particle
belongs to one unit cell can be calculated.
21. RULES:- 1. Paticles present at corner are shared between 8
cells. So each unit cell gets the share of 1/8th of
that particle.
2. Paticles present at centre of the face are shared
by 2 cells. So each unit cell gets the share of
1/2th of that particle.
3. Paticles present at centre of the cube is not
shared by any cell. So each unit cell gets a share.
4. A particle present at the mid point of an edge of
a crystall is shared by 4 unit cell. So each nuit
cell gets a share of 1/4th of particle.
number of particles present in
Simple cube= 1/8 X 8 = 1 particle
Body centred unit cells= (1/8 X 8 ) + 1 = 2 particle
Face centred unit cells= (1/8 X 8) + (1/2 X 6) = 4 particle
22. The simple ionic crystals are made up of only
two elements.
Eg: NaCl, CaCl2, K2O etc
23. Ionic crystals are classified in to two types
based on relative number of positive and
negetive ions.
1. AB TYPE Crystals
Eg: NaCl, KCl, LiBr, KBr NaI, CsCl
Crystals having same number of +ve and –ve ions.
24. 1. AB2 and A2B TypeCrystals
Crystals having ions double than the other
Eg: CaF2, MgCl2 Na2O Etc
Li2O
25. Ionic radius is defined sa the distance
between the nucleus of an ion and the point
upto which its nuclear charge has influence
on its electron cloud. It is determined by
X- ray Or electron difraction studies.
When atomic number of elements increases along a
period in the periodic table, the ionic radius
decreases because of the increase in the effective
nuclear charge of the ion.
26.
27. ION N3- O2- F- Na+ Mg2+
Atomic No. 7 8 9 11 12
Ionic Radius
in nm
0.171 0.140 0.136 0.095 0.06
Ion Atomic No. Ionic Radius
F- 9 0.136
Cl- 17 0.181
Br- 35 0.195
I- 53 0.216
Li+ 3 0.060
Na+ 11 0.095
K+ 19 0.133
Rb 37 0.148
The ionic radius
increases with the
increase of atomic
number down the group
because of the addition
of new Shells.
28. Radius ratio is the ratio of the size of cation to
size of anion present in an ionic crystal.
Radius ratio = r+
r-
Radius ratio of NaCl = rNa =0.095 = 0.52
rCl 0.181
Radius ratio of ZnS = 0.40, CsCl =0.93,
CaF2=0.73
29. Relation between radius ratio and
Coordination Number
When the radius ratio increases, cation is
surrounded by more number of anion. Hence
larger the size of cation, higher is the
coordination number.
Limiting radius
ratio
Coordination
Number
Shape of the
molecule
Example
0.155 to 0.225 3 Triangular Boron trioxide
0.225 to 0.414 4 Tetrahedral Znic blend
0.414 to 0.732 6 Octahedral Rock Salt
0.732 to 1.0 8 Body centred
cubic
Caesium Chloride
