Chapter
7
Nuclear Chemistry
“The branch of chemistry which deals with the study of composition applying electric and magnetic fields. When these radiation were subjected
of atomic nucleus and the nuclear transformations is known as nuclear to electric or magnetic field, these were split into three types , and –
chemistry”. rays.
The common examples of nuclear processes are radioactivity, Characteristics of radioactive rays
artificial transmutations, nuclear fission and nuclear fusion. The nuclear is -Ray -Ray -Ray
also an important aspect of chemistry because the energies involved in some Charge and mass : It carries +2 It carries -1 charge and It has no charge
of these are million times greater than those in ordinary chemical reactions. charge and 4 unit mass. no mass. and negligible
mass.
Radioactivity
Identity : Helium nuclei or High energy
“Radioactivity is a process in which nuclei of certain elements Electron 1e 0 raditons.
undergo spontaneous disintegration without excitation by any external helium ion 2 He 4 or He2+.
means.’’ and the elements whose atoms disintegrate and emit radiations are Action of magnetic field : Deflected to anode. Not deflected.
called radioactive elements. Deflected towards the cathode.
Henry Becquerel (1891) observed the spontaneous emission of Velocity : 1/10th to that of light. Same as that of light. Same as that of
light.
invisible, penetrating rays from potassium uranyl sulphate
Ionizing power : Very high Low nearly 100 times to Very low.
K 2 UO2 (SO4 )2 , which influenced photographic plate in dark and were nearly 100 times to that of - that of -rays.
able to produce luminosity in substances like ZnS. rays.
Later on, M.M. Curie and her husband P. Curie named this Effect on ZnS plate : They Very little effect. Very little effect.
cause luminescence.
phenomenon of spontaneous emission of penetrating rays as, Radioactivity.
Penetrating power : Low 100 times that of - 10 times that of -
Curies also discovered a new radioactive element Radium from particles. particles.
pitchblende (an ore of U i.e. U3 O8 ) which is about 3 million times more Range : Very small. More than -particles. More
radioactive than uranium. Now a days about 42 radioactive elements are Nature of product : Product Product obtained by the There is no change
known. obtained by the loss of 1 - loss of 1 -particle has in the atomic
particle has atomic number atomic number more by number as well as
The radioactivity may be broadly classified into two types, less by 2 units and mass 1 unit, without any in mass number.
(1) If a substance emits radiations by itself, it is said to possess number less by 4 units. change in mass number.
natural radioactivity.
(2) If a substance starts emitting radiations on exposure to rays
Theory of radioactivity disintegration
from some natural radioactive substance, the phenomenon is called induced Rutherford and Soddy, in 1903, postulated that radioactivity is a
or artificial radioactivity. nuclear phenomenon and all the radioactive changes are taking place in the
Radioactivity can be detected and measured by a number of devices nucleus of the atom. They presented an interpretation of the radioactive
like ionisation chamber, Geiger Muller counter, proportional counter, flow processes and the origin of radiations in the form of a theory known as
counter, end window counter, scintillation counter, Wilson cloud chamber, theory of radioactive disintegration. The main points of this theory are,
electroscope, etc. (1) The atomic nuclei of the radioactive elements are unstable and
Nature and characteristics of radioactive emissions liable to disintegrate any moment.
The phenomenon of radioactivity arises because of the decay of (2) The disintegration is spontaneous, i.e., constantly breaking. The
unstable nuclei or certain element. rate of breaking is not affected by external factors like temperature,
Photographic plate pressure, chemical combination etc.
The nature of the radiations emitted
from a radioactive substance was
investigated by Rutherford (1904) by
Radioactive
Lead block substance
Fig. 7.1
, (3) During disintegration, atoms of new elements called daughter To determine the number of - and - particles emitted during the
elements having different physical and chemical properties than the parent nuclear transformation. It can be done in following manner,
elements come into existence. a
c X bd Y x 42 He y 1 e 0
(4) During disintegration, either alpha or beta particles are emitted
from the nucleus. ab
a b 4 x or x .....(i)
The disintegration process may proceed in one of the following two 4
ways, c d 2x y .....(ii)
(i) -particle emission : When an -particle (2 He ) is emitted 4 where x = no. of -emitted, y = no. of -emitted
from the nucleus of an atom of the parent element, the nucleus of the new substituting the value of x from eq. (i) in eq. (ii) we get
element, called daughter element possesses atomic mass or atomic mass ab a b
c d 2 y ; y d c
number less by four units and nuclear charge or atomic number less by 2 4 2
units because -particle has mass of 4 units and nuclear charge of two
units. Radioactive disintegration series
Parent element -α Daughter element
The phenomenon of natural radioactivity continues till stable nuclei
Atomic mass : W W 4
are formed. All the nuclei from the initial element to the final stable
Atomic number : Z Z 2 element constitute a series known as disintegration series. Further we know
(ii) -particle emission : -particle is merely an electron which has that mass numbers change only when -particles are emitted (and not
negligible mass. Whenever a beta particle is emitted from the nucleus of a when -particles are emitted) causing the change in mass of 4 units at each
radioactive atom, the nucleus of the new element formed possesses the step. Hence the mass numbers of all elements in a series will fit into one of
same atomic mass but nuclear charge or atomic number is increased by 1 the formulae. 4n, 4 n 1 , 4 n 2 and 4 n 3 , hence there can be only
unit than the parent element. Beta particle emission is due to the result of four disintegration series.
decay of neutron into proton and electron. 0 n1 1 p1 1e 0 4n 4n + 1 4n + 2 4n + 3
n 58 59 59 58
The electron produced escapes as a beta-particle-leaving proton in Parent element 232
90 Th 94 Pu 241 92 U
238
92 U
235
the nucleus.
Half life (yrs) 10
1.39 10 10 4.5 10 9 7.07 10 8
Parent element
-β
Daughter element
Atomic mass : W W Half life (yrs) 13.5
Atomic number : Z Z 1 1.39 10 10 2.2 10 6 4.5 10 9
(iii) -ray emission : -rays are emitted due to secondary effects. The Name of series Thorium Neptunium Uranium Actinium
(Natural) (Artificial) (Natural) (Natural)
excess of energy is released in the form of -rays. Thus -rays arise from End product 208
energy re-arrangements in the nucleus. As -rays are short wavelength 82 Pb 83 Bi 209 82 Pb
206
82 Pb
207
electromagnetic radiations with no charge and no mass, their emission from n 52 52 51 51
a radioactive element does not produce new element. Number of lost 6 8 8 7
particles
Special case : If in a radioactive transformation 1 alpha and 2 beta- 4 5 6 4
particles are emitted, the resulting nucleus possesses the same atomic Nuclear structure and Nuclear forces
number but atomic mass is less by 4 units. A radioactive transformation of
this type always produces an isotope of the parent element. According to an earlier hypothesis, the nucleus is considered as
α W 4 β W 4 β W 4 being composed of two building blocks, proton's and neutron's, which are
Z A W
Z 2 B
Z 1 C
ZD collectively called nucleons. The forces, which hold the nucleons together
A and D are isotopes. means stronger proton – proton, neutron – neutron and even proton –
neutron attractive forces, exist in the nucleus. These attractive forces are
Group displacement law called nuclear forces. Nuclear forces operate only within small distance of
Soddy, Fajans and Russell (1911-1913) observed that when an - about 1 10 15 m or 1 fermi (1 fermi = 10 13 cm ) and drops rapidly to
particle is lost, a new element with atomic number less by 2 and mass
number less by 4 is formed. Similarly, when -particle is lost, new element zero at a distance of 1 10 13 cm. These are referred to as short range
with atomic number greater by 1 is obtained. The element emitting then forces. Nuclear forces are nearly 10 21 times stronger than electrostatic
forces.
or -particle is called parent element and the new element formed is called
daughter element. The above results have been summarized as, Yukawa in 1935, put forward a postulate that neutrons and protons
(1) When an -particle is emitted, the new element formed is are held together by very rapid exchange of nuclear particles called Pi-
displaced two positions to the left in the periodic table than that of the mesons (-mesons have mass equal to 275 times of the mass of an electron
parent element (because the atomic number decreases by 2). and a charge equal to +1, 0 or –1. These are designated as and + 0 –
(2) When a -particle is emitted, the new element formed is respectively). The nuclear force which is used in rapid exchange of Pi-
displaced one position to the right in the periodic table than that of the mesons between nucleons are also called exchange forces.
parent element (because atomic number increased by 1). The binding forces between unlike nucleons (p and n) are explained
(3) When a positron is emitted, the daughter element occupies its by the oscillation of a charged -meson ( or ) +
position one group to the left of the parent element in periodic table.
Group displacement law should be applied with great care especially (a) p1 n 2 n1 n 2 n1 p 2
in the case of elements of lanthanide series (57 to 71), actinide series (89 to
(b) p1 n 2 n1 p 2 n1 p 2
103), VIII group (26 to 28; 44 to 46; 76 to 78), IA and IIA groups.
Binding forces between like nucleons (p - p or n - n) result from the
exchange of neutral mesons ( ) as represented below.
0
7
Nuclear Chemistry
“The branch of chemistry which deals with the study of composition applying electric and magnetic fields. When these radiation were subjected
of atomic nucleus and the nuclear transformations is known as nuclear to electric or magnetic field, these were split into three types , and –
chemistry”. rays.
The common examples of nuclear processes are radioactivity, Characteristics of radioactive rays
artificial transmutations, nuclear fission and nuclear fusion. The nuclear is -Ray -Ray -Ray
also an important aspect of chemistry because the energies involved in some Charge and mass : It carries +2 It carries -1 charge and It has no charge
of these are million times greater than those in ordinary chemical reactions. charge and 4 unit mass. no mass. and negligible
mass.
Radioactivity
Identity : Helium nuclei or High energy
“Radioactivity is a process in which nuclei of certain elements Electron 1e 0 raditons.
undergo spontaneous disintegration without excitation by any external helium ion 2 He 4 or He2+.
means.’’ and the elements whose atoms disintegrate and emit radiations are Action of magnetic field : Deflected to anode. Not deflected.
called radioactive elements. Deflected towards the cathode.
Henry Becquerel (1891) observed the spontaneous emission of Velocity : 1/10th to that of light. Same as that of light. Same as that of
light.
invisible, penetrating rays from potassium uranyl sulphate
Ionizing power : Very high Low nearly 100 times to Very low.
K 2 UO2 (SO4 )2 , which influenced photographic plate in dark and were nearly 100 times to that of - that of -rays.
able to produce luminosity in substances like ZnS. rays.
Later on, M.M. Curie and her husband P. Curie named this Effect on ZnS plate : They Very little effect. Very little effect.
cause luminescence.
phenomenon of spontaneous emission of penetrating rays as, Radioactivity.
Penetrating power : Low 100 times that of - 10 times that of -
Curies also discovered a new radioactive element Radium from particles. particles.
pitchblende (an ore of U i.e. U3 O8 ) which is about 3 million times more Range : Very small. More than -particles. More
radioactive than uranium. Now a days about 42 radioactive elements are Nature of product : Product Product obtained by the There is no change
known. obtained by the loss of 1 - loss of 1 -particle has in the atomic
particle has atomic number atomic number more by number as well as
The radioactivity may be broadly classified into two types, less by 2 units and mass 1 unit, without any in mass number.
(1) If a substance emits radiations by itself, it is said to possess number less by 4 units. change in mass number.
natural radioactivity.
(2) If a substance starts emitting radiations on exposure to rays
Theory of radioactivity disintegration
from some natural radioactive substance, the phenomenon is called induced Rutherford and Soddy, in 1903, postulated that radioactivity is a
or artificial radioactivity. nuclear phenomenon and all the radioactive changes are taking place in the
Radioactivity can be detected and measured by a number of devices nucleus of the atom. They presented an interpretation of the radioactive
like ionisation chamber, Geiger Muller counter, proportional counter, flow processes and the origin of radiations in the form of a theory known as
counter, end window counter, scintillation counter, Wilson cloud chamber, theory of radioactive disintegration. The main points of this theory are,
electroscope, etc. (1) The atomic nuclei of the radioactive elements are unstable and
Nature and characteristics of radioactive emissions liable to disintegrate any moment.
The phenomenon of radioactivity arises because of the decay of (2) The disintegration is spontaneous, i.e., constantly breaking. The
unstable nuclei or certain element. rate of breaking is not affected by external factors like temperature,
Photographic plate pressure, chemical combination etc.
The nature of the radiations emitted
from a radioactive substance was
investigated by Rutherford (1904) by
Radioactive
Lead block substance
Fig. 7.1
, (3) During disintegration, atoms of new elements called daughter To determine the number of - and - particles emitted during the
elements having different physical and chemical properties than the parent nuclear transformation. It can be done in following manner,
elements come into existence. a
c X bd Y x 42 He y 1 e 0
(4) During disintegration, either alpha or beta particles are emitted
from the nucleus. ab
a b 4 x or x .....(i)
The disintegration process may proceed in one of the following two 4
ways, c d 2x y .....(ii)
(i) -particle emission : When an -particle (2 He ) is emitted 4 where x = no. of -emitted, y = no. of -emitted
from the nucleus of an atom of the parent element, the nucleus of the new substituting the value of x from eq. (i) in eq. (ii) we get
element, called daughter element possesses atomic mass or atomic mass ab a b
c d 2 y ; y d c
number less by four units and nuclear charge or atomic number less by 2 4 2
units because -particle has mass of 4 units and nuclear charge of two
units. Radioactive disintegration series
Parent element -α Daughter element
The phenomenon of natural radioactivity continues till stable nuclei
Atomic mass : W W 4
are formed. All the nuclei from the initial element to the final stable
Atomic number : Z Z 2 element constitute a series known as disintegration series. Further we know
(ii) -particle emission : -particle is merely an electron which has that mass numbers change only when -particles are emitted (and not
negligible mass. Whenever a beta particle is emitted from the nucleus of a when -particles are emitted) causing the change in mass of 4 units at each
radioactive atom, the nucleus of the new element formed possesses the step. Hence the mass numbers of all elements in a series will fit into one of
same atomic mass but nuclear charge or atomic number is increased by 1 the formulae. 4n, 4 n 1 , 4 n 2 and 4 n 3 , hence there can be only
unit than the parent element. Beta particle emission is due to the result of four disintegration series.
decay of neutron into proton and electron. 0 n1 1 p1 1e 0 4n 4n + 1 4n + 2 4n + 3
n 58 59 59 58
The electron produced escapes as a beta-particle-leaving proton in Parent element 232
90 Th 94 Pu 241 92 U
238
92 U
235
the nucleus.
Half life (yrs) 10
1.39 10 10 4.5 10 9 7.07 10 8
Parent element
-β
Daughter element
Atomic mass : W W Half life (yrs) 13.5
Atomic number : Z Z 1 1.39 10 10 2.2 10 6 4.5 10 9
(iii) -ray emission : -rays are emitted due to secondary effects. The Name of series Thorium Neptunium Uranium Actinium
(Natural) (Artificial) (Natural) (Natural)
excess of energy is released in the form of -rays. Thus -rays arise from End product 208
energy re-arrangements in the nucleus. As -rays are short wavelength 82 Pb 83 Bi 209 82 Pb
206
82 Pb
207
electromagnetic radiations with no charge and no mass, their emission from n 52 52 51 51
a radioactive element does not produce new element. Number of lost 6 8 8 7
particles
Special case : If in a radioactive transformation 1 alpha and 2 beta- 4 5 6 4
particles are emitted, the resulting nucleus possesses the same atomic Nuclear structure and Nuclear forces
number but atomic mass is less by 4 units. A radioactive transformation of
this type always produces an isotope of the parent element. According to an earlier hypothesis, the nucleus is considered as
α W 4 β W 4 β W 4 being composed of two building blocks, proton's and neutron's, which are
Z A W
Z 2 B
Z 1 C
ZD collectively called nucleons. The forces, which hold the nucleons together
A and D are isotopes. means stronger proton – proton, neutron – neutron and even proton –
neutron attractive forces, exist in the nucleus. These attractive forces are
Group displacement law called nuclear forces. Nuclear forces operate only within small distance of
Soddy, Fajans and Russell (1911-1913) observed that when an - about 1 10 15 m or 1 fermi (1 fermi = 10 13 cm ) and drops rapidly to
particle is lost, a new element with atomic number less by 2 and mass
number less by 4 is formed. Similarly, when -particle is lost, new element zero at a distance of 1 10 13 cm. These are referred to as short range
with atomic number greater by 1 is obtained. The element emitting then forces. Nuclear forces are nearly 10 21 times stronger than electrostatic
forces.
or -particle is called parent element and the new element formed is called
daughter element. The above results have been summarized as, Yukawa in 1935, put forward a postulate that neutrons and protons
(1) When an -particle is emitted, the new element formed is are held together by very rapid exchange of nuclear particles called Pi-
displaced two positions to the left in the periodic table than that of the mesons (-mesons have mass equal to 275 times of the mass of an electron
parent element (because the atomic number decreases by 2). and a charge equal to +1, 0 or –1. These are designated as and + 0 –
(2) When a -particle is emitted, the new element formed is respectively). The nuclear force which is used in rapid exchange of Pi-
displaced one position to the right in the periodic table than that of the mesons between nucleons are also called exchange forces.
parent element (because atomic number increased by 1). The binding forces between unlike nucleons (p and n) are explained
(3) When a positron is emitted, the daughter element occupies its by the oscillation of a charged -meson ( or ) +
position one group to the left of the parent element in periodic table.
Group displacement law should be applied with great care especially (a) p1 n 2 n1 n 2 n1 p 2
in the case of elements of lanthanide series (57 to 71), actinide series (89 to
(b) p1 n 2 n1 p 2 n1 p 2
103), VIII group (26 to 28; 44 to 46; 76 to 78), IA and IIA groups.
Binding forces between like nucleons (p - p or n - n) result from the
exchange of neutral mesons ( ) as represented below.
0
