Unit cells, Types of unit cells, close packing, packing fraction, radius ratio, electrical and magnetic properties of solids.

1. THE SOLID STATE
SUBJECT – CHEMISTRY
CLASS – XII
TEACHER’S NAME – RAJESH TRIVEDI

2. Contents:
* Close packing.
* Unit cells.
* Types of unit cells.
* Number of atoms per unit cell.
* Radius ratio.
* Coordination number .
* Imperfections of the solids.
* Electrical and magnetic properties of solids.

3. CLOSE PACKING IN SOLIDS

4. Three dimensional close packing

5. THE SMALLEST GROUP OF PARTICLES WHICH WHEN REPEATED
OVER AND OVER AGAIN TO PRODUCE A COMLETE SPACE
LATTICE KNOWN AS UNIT CELL
SIMPLE CUBIC UNIT CELL SPACE LATTICE OF SIMPLE CUBIC UNIT CELL

6. FACE CENTERED CUBIC UNIT
CELL
COMPLETE SPACE ATTICE OF FACE
CENTERED CUBIC UNIT CELL

7. BODY CENTERED CUBIC UNIT
CELL
COMPLETE SPACE ATTICE OF BODY
CENTERED CUBIC UNIT CELL

8. The smallest group of atoms which when
repeated over and over again to produce a
space lattice known as unit cell

9. Types of unit cells :
Simple cubic Body centered Face centered

10. WHAT IS THE POSITIONS OCCUPIED
BY ATOMS IN THE UNIT CELL ????

11. DON’T WORRY I WILL TRY TO SHO YOU
WITH THE HELP OF PICTURES.

12. Actual structure showing the positions of
the atoms shared in various unit cells
1/8 Corner atoms 1 body atom ½ centre atom
Simple cubic unit cell Body centred cubic unit cell Face centred cubic unit cell

13. Number of atom per unit cell
8×⅛ = 1 (8 ×⅛) + (6×½) =4 (8×⅛ ) + 1 = 2

14. Packing fraction for the unit cells
Body centred
Face centred

15. Packing fraction of hcp unit cell

16. Imperfections in the solids
Schottky defect Farenkel defect

17. Metal excess defects
Due to anion vacancy Extra cation in the Interstitial site

18. Metal deficiency defects
By Cation Vacancy

19. Explanation for the electrical properties with
the help of BAND theory

20. Conductivity of ::::::
* Conductors :
* 104 – 107 Ω –1 m–1
* Semi – conductors :
* 10–6 – 104 Ω –1 m–1
* Insulators :
* 10–10 – 10– 20 Ω –1 m–1

21. Magnetic properties of solids on the
basis of alignment of their magnetic
moments
Diamagnetic substances
Ferromagnetic substances
Anti – ferromagnetic substances
Paramagnetic substances
Ferrimagnetic substances

22. Exercises
Q.1. What is the meaning of close packing ?
Q.2. What do you mean by coordination number ?
Q.3. What is the number of atom per unit cell for fcc lattice ?
Q.4. What is the packing fraction of hcp lattice ?
Q.5. What type defects are known as schottky defects ?
Q.6. What is the conductivity of insulators ?
Q.7. What do you mean by forbidden zone ?
Q.8. What is the main differences between ferrimagnetic and ferromagnetic solids ?
Q.9. What is the radius ratio of tetrahedral geometry ?
By – Rajesh Trivedi ( PGT – Chem)