F.Y.B.Sc ( As per SPPU)

1. Chapter- 3
Physics of Molecules

2. Molecular physics is the study of the physical
properties of molecules, the chemical bonds
between atoms as well as
the molecular dynamics.
States of Matter:-
1)Solid
2)Liquid
3)Gas
4)Plasma

4. Molecule :-
An electrically neutral group of two or
more atoms held together by chemical bonds.
Types:-
Homonuclear :- Molecules composed of only one
element.
Ex:- H2 , O2 , N2 ,O3, halogens ……….etc.

5. Heteronuclear :- Molecule composed of atoms of
more than one element.
Ex:-H2O ,N2O, Co2 ………………….etc

6. Forces Between Atoms
1)Attractive Force
2)Repulsive Force

9. Potential Energy Curve :- Interaction in Atoms
Bond
Length

11. The Attractive interatomic Forces reflect
presence of bonds between atoms.
Bond:- Force of attraction which holds the
two atoms or ions together in molecule.
Types of Bonding:-
1)Ionic
2) Covalent
3)Metallic
4)Van der Waals interactions.

12. Ionic Bond
It is chemical bonding that involves the electrostatic
attraction between oppositely charged ions , or
between two atoms with sharply different electro
negativities.
Requirement :-
1)Electropositive ( Metal)
2)Electronegative (Nonmetal)
3) Difference in electro negativity larger

13. 2 , 8 , 1 2 , 8 ,7
Formation of ionic bond is always Exothermic reaction!

14. Characteristics of Ionic Bond
1)Strong Bond with cohesive energy 5 – 10 eV
2)Hard , High Melting , Boiling points
3)Soluble in ionizing solvents such as water
4)Polar bond

15. Covalent Bond
A chemical bond that involves the sharing of
electron pairs between atoms.
These electron pairs are known as shared
pairs or bonding pairs.
Requirement :-
Atoms must have Same electronegativity

19. Physical Properties of Covalent Bond
1) Strongly Directional: -
Orientation of atoms in space with respect to each
other

20. 2)Covalent Compounds are mostly liquids & Gases
3)Cohesive energy is of 6-12 eV/atom
4) insoluble in all ordinary liquids
NH3
H2O

21. 5)Hard , high melting point, boiling point
Ex:- Diamond is the hardest substance (M.P. 3280 oK)

22. 5) Electrical Conductivity is wide
a) Insulators : cl2 , F2
b) Semiconductor: Si ,Ge (temperature dependence)

23. Types of Covalent Bond
1)Polar Covalent Bond :-
 Because of Difference in electronegativity
Unequal sharing of electron
2) Nonpolar Covalent Bond:-
 electronegativity Difference = 0
 Equal sharing of electron

24. Polar Covalent Bond

26. Nonpolar Covalent Bond

27. Types of Covalent Bond depending upon the number
of shared electron pair
1)Single Covalent Bond
2) Double Covalent Bond
3)Triple Covalent Bond

29. Vander Waal’s Bond
Vander Waal’s Bond Forces include attraction and repulsions
between atoms, molecules ( Inert gas atoms such as He, Ne,
…etc) and surfaces, as well as other intermolecular forces.
 Due to interaction between electric dipoles of atoms or
molecules.
 Bond energy :- 0.1 eV or less
Polar Molecules
 Nonpolar Molecules

30. Nonpolar Molecules Polar Molecules