# CBSE Class 12 Chemistry Notes : Solid State

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CBSE Class 12 Chemistry Notes : Solid State – If you are looking for Solid State notes than this is perfect place for you where you can find easy Solid State notes

A solid is defined as that form of matter which has rigidity and due to which possess a definite volume and a definite shape. These characteristics are due to the existence of very strong forces of attraction among the constituent species of the solid.

## Classification of Solids

##### 1. Crystalline solids

They have systematic and regular arrangement of particles and sharp melting point. They have flat faces and sharp edges. Sodium chloride and quartz are typical example of crystalline solids.

##### 2. Amorphous solids

They are unsystematic and irregular arrangement of particles. On the basis of types of bond present, they are further divided into for groups

• Molecular solid or van der Waal’s solid, e.g. l2(s),H2O(s)etc.
• Network solid or covalent solids, e.g. graphite diamond,etc.
• Metallic solid e.g. all metallic solids,etc.
• Ionic solid e.g. Nacl, CsCl, ZnS, etc. Note Crystalline solids are anisotropic, i.e. their physical properties have same values in different directions while amorphous solids are isotropic, i.e. their physical properties have sames values in different directions.

Crystal Lattice- A regular arrangement of the constituent particles or crystal in the 3d (three- dimensional) spaces in known a crystal lattice or space lattice.There are only 14 possible three-dimensional lattice known as Bravis lattice.

Unit Cells- The smallest portion of there crystal lattice which repeated in different direction, generates the entire lattice is known as unit cell.
Unit cell is broadly divided into two classes

(a) Primitive unit cell – When constituent particles are present only on the corner positions of the unit cell, then unit cell is called primitive unit cell.                                  Primitive unit cells are of seven types

 i) Cubic ii) Tetragonal iii) Ortho rhombic iv) Hexagonal v) Rhombohedral vii) Monodinic viii) Triclinic

(b) Centred unit cell- hen a unit cell contains one or more constituent particles present at positions other than corners in addition to those at corners, it is called as centred unit cell. This is of three types

a) Body- centred unit cell- In addition to the particles at the corners, there is one particles present at the centre of body of the unit cell.

b) Face-centred unit cell- In addition of the particles at the corners, there is one particle present at the centre of it face.

c) End-centred unit cell- Here in the addition to the particles at the corners, there is one particle each at the centre of any two opposites faces.

##### Number of Atoms in a Unit Cell

a) simple unit cells (sc)  or primitive unit cell– In which particles are present only at corners… Number of atoms per unit cell= 1/8×8=1

2) face centred cubic fcc unit cell- in which the particles are present at the corners as well as at the centre of each face..

number of atoms per unit          cell=1/8 x 8+1/2 x 6= 4

3) body centred cubic BCC unit cell- in which the particles are present at the corners of the cube as well as one particle is present at the centre with in the body..

Number of atoms per unit cell = 1/8×8+1=2

### Closed Packed  Structures

The packing of spheres of equal size takes place as follows
1- One Dimensional Packing When the spheres are placed in horizontal row touching         each other, an edge of the crystal is formed.

2-Two Dimensional Packing–  It is of two types

a- Square close packing SCP- The particles when placed in the adjacent rows, shows a         horizontal as well as vertical alignment and form squares.

b-Hexagonal close packing hcp-  The particles in every next row are placed in the             depression between the particles of the first row . The particles in the third row will be         vertically aligned with those in the first row.

3- Three dimensional packing– It is of two types
a- Hexagonal close packing hcp- When the first layer is placed as layer and second             layer as layer b, then the arrangement is called AB AB…..
Pattern or hexagonal closed packing hcp.

## CBSE Class 12 Chemistry Notes : Solid State

b- Cubic close packing CCP- When the third layer is placed over the second layer in such      a way that spheres cover the octahedral voids, a layer different from layers A and B is        produced . Let us call it as layer C. This pattern of stacking spears is called ABC ABC           ….pattern or cubic closed packing . It is similar to face centred cubic packing.

Voids– In closed packed structure, the input in space is called interstitial site or void. The void maybe a simple triangular area within the case of 2 dimensional packing and known as the symmetric void.

In three dimensional closed packing patterns comma the voids can be two types-

1- Tetrahedral void– A void surrounded by four spheres occupying the corners of                  tetrahedron is called tetrahedral void.

2- Octahedral void– A void is surrounded by 6 is pair along the corners of an                        octahedron is called octahedral void.

The sizes of above written words can be seen in increasing order

Trigona< tetrahedral< octahedral

Coordination number-  Coordination number is the number of atoms are ions or molecules surrounding a particular atom in a crystal lattice.

Packing efficiency– It is the percentage of total space filled by the particles in a unit cell. Latest calculate the packing efficiency in various type of structures

$Packing efficiency=\frac { { volume occupied by 4 spares in the unit cell }\times { 100 } }{ total volume of a unit cell }$

Calculations involving unit cell dimensions

Density of the unit cell [d]  = mass of the unit cell/volume of the unit cell

$d = \frac {{M} \times {Z}}{{N}_{A} \times {a}^{3}}$

Where d = density

M=molecular weight

Z=number of atoms in per unit cell

NA= Avogadro number

a= edge length of unit cell

Point defects- They are the irregularities from idol arrangement around a point. Point defect further divided into stoichiometry and non-stoichiometry defect.

Vacancy defects– This occur when positions (lattice site) that should contain atoms or ions are vacant. This result in decrease in density. Scotty defect is basically a vacancy defect shown by ionic solids.

Interstitial defects- This occurs when some constituent particle occupy an interstitial site. This defect increases the density of the substance. Frankel defect is just like interstitial defect shown by ionic solids.

Frenkel defect– This defect arises when the smaller iron usually cation is dislocated from its normal site to interstitial site. It creates a vacancy defect at its real site and an interstitial defect at its new location. This defect is generally found in ionic crystals where anion is much larger in size then the cation. It is also known as dislocation defect. Example agbr, agcl agi, zns , etc. Due to small size of Ag+ and zn²+ ions. Due to this defect, electrical conductivity increases to a small extent. In this defect density remains same.

Schotty defects- This occur due to missing of atoms or ions from the lattice point. In order to keep up electrical neutrality, the number of missing cations and anions are equal. In this defect density of the substance decreases. It is shown by  KCL, NaCl and agbr.

### Electrical Properties

Solids exhibit an amazing range of Electrical conductivities extending over 27 order of magnitude ranging from solids are classified into three groups on the basis of conduction power, namely
Conductors – The solids with conductivity ranging between 104 to 107 Ω-1 m-1 are called conductors.

Semiconductors – The solids which exhibit intermediate conductivities, ranging from 10-6 to 10-4 Ω-1 m-1  are called semiconductors.

Insulators –The solids which have very low conductivity values, ranging from 10-20 to   10-10 Ω-1 m-1 are called insulators.

#### Doping

Addition of small amount of foreign impurity in the host crystal is called as doping. It increases the electrical conductivity.

On the basis of impurities added for doping, semiconductors are of two types- (a) n-type semiconductor (b) p-type semiconductor

### Magnetic Properties

• Paramagnetic substance– Show magnetic behavior only under the influence of the applied magnetic field.
• Ferromagnetic substance Exhibits magnetism even when applied magnetic fild is removed.
• Antiferromagnetic substance Have no magnetic moment since the electronic spins mutually cancel under the influence of external magnetic field.
• Ferrimagnetic substance Exhibit some magnetic character due to alignment of the electron spins in parallel and antiparallel directions in unequal numbers.
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