Main Points : "Nuclear Chemistry", natural radioactivity, artificial radioactivity, induced radioactivity, Cause of Radioactivity, Nature and characteristics of Radioactive Substances, Alpha rays, Gama rays, Beta rays, rate of radioactive disintegration, decay, Half Life Period, nuclear fission, Nuclear Fusions Project on Nuclear Chemistry
NUCLEAR CHEMISTRY INTRODUCTION
In ordinary chemical combinations, only the electrons present in the
Outermost orbitlas are involved i.e. they are transferred from one atoms to
the other atom remain unaffected. However, there are certain phenomena in
which the nucleus of the atom is involved. “The branch of chemistry dealing
with the phenomena involving the nuclei of the atoms is known as
nuclear chemistry.
In fact, the only phenomena involving the nucleus of an atom is
radio activity - both natural
and artificial.
natural radioactivity :
The
phenomenon of spontaneous emission of certain kinds of radiations by some
elements is called radioactivity or natural radioactivity.
artificial or induced radioactivity :
The
phenomenon is which the artificial disintegration of a stable nucleus leads
to the formation of a radioactive isotope is called artificial
radioactivity.
Cause
of Radioactivity
It has been found that the nuclei of those atoms are stable whose ratio of
the neutrons to protons (n/p ratio) lies in the range 1 to 1.5. If number of
neutrons is plotted against the number of protons, the table nucleus lie in
a well defined belt, called stability belt as shown in Fig. the nuclei with
atomic number upto 20 have n/p ratio close to 1. The nuclei with n/p
ration lying above or below the stability particles so that their n/p ration
falls with in the stability belt. Loss of 
particle
(2p and 2n) increases the n/p ration where as loss of 
particles
increases the number of protons and hence decreases the n/p ratio.
Nature and characteristics of Radioactive Substances
It is observed that an applying the field, the rays emitted from the
radioactive substances are separated into three types called 
rays.
The rays are deflected in a direction which shows that they carry
positive charges the 
rays
are deflected in the opposite direction and the 
rays
are not deflected at all showing that they carry no charge.
properties of
a
rays :
(i)
The direction of deflection of the
a
rays in the electric and magnetic field show that they carry positive
charge. It is found that each particle carries two units of
positive charges and has mass nearly four times that of hydrogen atom.
(ii) The velocity of rays is found to be nearly 1/10 the 1/20
the of that of light, depending upon the nature of source.
(iii)
a
rays ionize the gas through which they pass.
(iv)
a
rays have low penetrating power. They can penetrate through air only to a
distance of about 7 cm.
(v)
a
rays affect a photographic plate and produce luminescence when they strike a
line sulphide screen.
properties of
b
rays
(i)
The direction of deflection of
b
rays in the electric and magnetic fields shows that they carry negative
charge. These particles possess the same charge and mass as that of the
electrons.
(ii) The velocity of
b
rays depends upon the nature of the source. The speed of
b
particles varies from 3% to 99% of that of light i.e. in same cases it
approaches the velocity of light.
(iii) The ionizing power of
b
particles is about 1/100th of that of
a
particles.
(iv) Their penetrating power is about 100 times greater than that of
a
rays.
(v) Like rays,
b
rays affect a photographic plate and the effect is much higher. However,
there is no significant effect on a zinc sulphide screen become of their
lower kinetic energy.
properties of
g
rays
(i)
They are not deflected in the electric and magnetic fields showing
these by that they do not carry any charge.
(ii) They travel with the same velocity as that of light.
(iii) As they do not have any mass, their ionizing power is very poor.
(iv) Their penetrating power is about 100 times more than that of
b
rays. Thus they can penetrate through lead sheets as thick as 150 mm.
(v)
g
rays have very little effect on the photographic plates or zinc. sulphide
screen.
rate of radioactive
disintegration or decay
The
rate of disintegration depends only upon the nature of the radioactive
element and the radioactive disintegration follows first order kinetics and
hence the expression for the rate constant (g).
Where “No is
the number of the atoms taken initially.
and “N” is the number of atoms present at any instant of time.
The equation is also written as :
Where a is the amount of the radioactive substance initially taken and a-x
is the amount present at time t.
Half Life Period :
The half-life period of radioactive element is the time in which half of the
original substance disintegrate.
where
g
is disintegration constant.
nuclear fission
The splitting of
a heavier atom like that of uranium - 235 into a number of fragments of much
smaller mass by suitable bombardment of huge amount of energy is called
nuclear fission.
e.g. 
Huge
amount of energy.
Nuclear
Fusions
Nuclear fusions
is defined as a process in which lighter nuclei fuse together to form a
heavier nucleus.
H11
+ H11
----> H12
+ e10
Deuterium Positron
