The document provides an overview of nuclear chemistry, focusing on nuclear particles, their interactions, and reactions such as radioactive decay, fission, and fusion. It explains concepts like mass defect, binding energy, and introduces models like the liquid drop model to illustrate nuclear properties. Additionally, it distinguishes between radioactivity and artificial radioactivity while discussing the energy changes in nuclear reactions.

1. NUCLEAR CHEMISTRY
Shafna Jose
Assistant Professor
Department Of Chemistry
St. Mary’s College
Thrissur

2. INTRODUCTION
• Branch of chemistry deals with the of study of nuclear particles, nuclear forces
and nuclear reactions.
• Nucleus contains positively charged protons and electrically neutral neutrons
collectively known as nucleons.
• Atomic number : number of protons present in the nucleus.
• Mass number : The sum of protons and neutrons in a nucleus.
Nuclear Chemistry, Shafna Jose, St. Mary’s College.

3. • Each nuclide is defined by the number of protons ‘Z’ and
number of neutrons 'N’ that it’s nucleus contains.
• The general representation of a nuclide is given as
A X Z
X – denotes chemical symbol
Z – Atomic number( number of protons )
A – Mass number (number of neutrons + number of protons )
• Examples are 16O8,
31P15,
238U92 , etc.
Nuclear Chemistry, Shafna Jose, St. Mary’s College.

4. Theory of radioactive disintegration :
• Atoms of all radioactive elements undergo spontaneous disintegration with the emission of α or
β particles.
• Modes of decay : α –emission or β- emission.
α –emission : When a radionuclide decays by emitting an α particle, the atomic number decreases
by 2 units and mass number increases by 4 units.
Examples are :
238U92 → 234 Th90 + 4He2
215 Po 84 → 211 Pb82 + 4He2
Nuclear Chemistry, Shafna Jose, St. Mary’s College.

5. β- emission : When a radionuclide decays by emitting an β- particle atomic number
increases by 1 unit and on change in mass number.
Examples are :
234 Th 90 → 234Pa91 +
0e-1
211 Pb 82 → 211Bi83 + 0e-1
• The increase in nuclear charge and emission of electron from the nucleus takes place
due to the conversion of a neutron into a proton and an electron during the process.
• The γ rays emitted as a secondary effect of α- or β- emission.
Nuclear Chemistry, Shafna Jose, St. Mary’s College.

6. Mass Defect
• It is equal to the mass lost as an equivalent amount of energy during the formation of a given nucleus
from the component nucleons.
• If M, mp and mn are the masses of the nucleus (AXZ), a proton and a neutron, respectively, then
∆m = Zmp + Nmn – M = Zmp + (A – Z)mn - M
Binding Energy
• Energy released during the formation of a nucleus from it’s constituent nucleons.
• If ∆m is the mass defect , then binding energy , B.E = ∆mc2 .
B.E = [ Zmp + (A – Z)mn – M]c2
Nuclear Chemistry, Shafna Jose, St. Mary’s College.

7. Liquid Drop Model
Bohr tried to compare properties of a nucleus with a drop of a liquid and found many
similarities. Some of them are given below.
• Liquid drop has a large no: of molecules just like a nucleus has large no: of nucleons.
• Both the liquid drop and nucleus are homogenous and incompressible.
• Force between all the nucleons is same. Nuclear force is independent of charge and spin.
Nuclear Chemistry, Shafna Jose, St. Mary’s College.

8. • Heat of vaporization of a liquid corresponds to binding energy of nucleons in a
nucleus.
• Evaporation of a liquid corresponds to radioactive emission from a radioactive
isotope.
• In both liquid drop and nucleus, intermolecular forces are short range forces.
• By capturing high energy particle from outside nucleus form a compound nucleus as
does a liquid drop , to get excited.
Nuclear Chemistry, Shafna Jose, St. Mary’s College.

9. • Compound nucleus or the liquid drop may get de-excited by the following changes.
• Compound nucleus
a) By emission of radiation
b) By emission of a nucleon
c) By nuclear fission
• Liquid Drop
a)By cooling
b)By evaporation
c)By breaking up into droplets
• Two liquid drops undergo fusion and form a bigger drop, similarly lighter nuclei undergo
fusion and form a bigger nucleus.
Nuclear Chemistry, Shafna Jose, St. Mary’s College.

10. Nuclear Fission
• Splitting of a heavy nucleus into two fragments when bombarded with a suitable sub
atomic particle with the simultaneous release of a huge amount of energy.
235U92 + 0n1 → 144Ba56 + 20n1 + Energy
Fissile nuclides : undergo fission on bombardment with thermal or slow neutrons.
Eg: 239Pu94,
233U92
Fissionable nuclides : Require fast neutrons to produce their fission
Eg: 231Pa91,
238U92.
Critical mass : The minimum amount of the target material required to sustain a fission
chain reaction at a constant rate
Nuclear Chemistry, Shafna Jose, St. Mary’s College.

11. Nuclear Fusion
• Process in which lighter nuclei fuse together to form a heavier nucleus with the simultaneous
release of a huge amount of energy.
1H3 + 1H1 → 4He2 + 20 MeV
3H1 + 2H1 → 4He2 +0n1 + 17.8 MeV
• Fusion requires high temperature.
• These reactions are also called thermonuclear reactions.
• The function of a hydrogen bomb is based on nuclear fusion which is initiated by energy
from a fission bomb.
• Fusion reactions are common in the interior of stars.
Nuclear Chemistry, Shafna Jose, St. Mary’s College.

12. Nuclear Reactions
• It involves changes in the number of nucleons present in the nucleus.
• Nuclear reactions leads to atomic transformations or transmutations.
• Nuclear reactions involve energies a million times greater than those involved in
chemical reactions.
• Nuclear reactions may be divided into two categories :
a) radioactivity
b) artificial radioactivity
Nuclear Chemistry, Shafna Jose, St. Mary’s College.

13. Radioactivity :
• The nucleus undergoes a spontaneous change, i.e., a change by itself.
Artificial radioactivity :
• The reaction is brought about artificially through the interaction of two lighter nuclei.
•
• This is done by bombarding a relatively heavier nucleus with a lighter nucleus.
Induced radioactivity :
• The products in a nuclear reaction are a heavy nucleus and a proton, a neutron, an α
particle or a γ - ray photon.
• If the heavy nucleus is unstable it may start disintegrating like the natural radioactive
elements.
Nuclear Chemistry, Shafna Jose, St. Mary’s College.

14. Q Values of Nuclear Reactions
• The complete equation for a nuclear reaction include the energy change of
the reaction as well.
• It is denoted by Q.
• Rutherford’s transmutation reaction can be represented as
7N14 + 4He2 → 17O8 + 1H1 + Q
where Q is the nuclear reaction energy.
• Q is +ve if the reaction is exoergic.
• Q is –ve if the reaction is endoergic.
Nuclear Chemistry, Shafna Jose, St. Mary’s College.

15. References :
Physical Chemistry – Puri, Sharma, Pathania.
Essentials of Nuclear Chemistry – H.J. Arnikar
Nuclear Chemistry, Shafna Jose, St. Mary’s College.