Solid State

Solids are the substances which have definite shape and volume.

Meaing of Solid

Types of solid

Solids which have definite geometrical shape and sharp melting point are called crystalline solid.

There are two types of Solids

crystalline solids are

Shining in light &

Anisotropic

Solids which have no definite geometrical shape and no sharp melting point are called amorphous solid.

Amorphous solids are

1. Not Shining in light

2. Particles are not arranged in regular order.

3. Isotropic.

Difference between

Crystalline solids Amorphous solid1 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.

Arragements of atoms/ions / molecules in crystals

Crystal Lattice

Lattice Point

Lattice Point

Types of Crystalline Solids

1. Ionic crystals are crystals containing ions in the lattice point

Eg : Na+ Cl- CsCl, MgCl2 Etc

2. Molecular crystals are crystals containing molecules in the lattice point

Eg : Ice, Dry ice, solid ammonia Etc

3. Covalent crystals are crystals containing covalently bonded atoms in the lattice point

Eg : Diamond, Carborundam, graphite and Qurtz

4. Metallic crystals are crystals containing definite geometrical arrangement of metal atoms in the lattice point

Eg : Cu, Zn, Li, Fe Etc.

Crystal LatticeCrystal 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.

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

OTHER TYPE OF UNIT CELL

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

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

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

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

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.

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 particleBody centred unit cells= (1/8 X 8 ) + 1 = 2 particle

Face centred unit cells= (1/8 X 8) + (1/2 X 6) = 4 particle

Ionic CrystalsThe simple ionic crystals are made up of only two elements.

Eg: NaCl, CaCl2, K2O etc

Types of Ionic CrystalsIonic 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.

1. AB2 and A2B TypeCrystals

Crystals having ions double than the other

Eg: CaF2, MgCl2 Na2O Etc

Li2O

Ionic RadiusIonic 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.

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 0.195I- 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.

Radius RatioRadius 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

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

STRUCTURE OF ROCK SALT ( Na+Cl-)