NUCLEAR CHEMISTRY (RADIOACTIVITY)
Week: SIX Date:
Period: Duration: 1 HR 20 MIN. Average age of learners: 17YEARS
Subject: CHEMISTRY Class: SS 3
Topic: NUCLEAR CHEMISTRY (RADIOACTIVITY)
Sub topic:
Reference materials:
(1) ESSENTIAL CHEMISTRY, TONALD PUBLISHERS, I. O ODESINA
(2) NEW SCHOOL CHEMISTRY, AFRICAN FIRST PUBLISHERS, OSEI YAW ABABIO
(3) INTERNET
Instructional materials: Phone
Entry behavior: The students have been taught density.
Behavioural objective: At the end of the lesson the students should be able to:
1. Mention characteristics of radioactivity
2. State the types of radiation and their respective properties.
3. List some detector devices of radiation.
4. Solve problem involve nuclear chemistry
5. Differentiate between nuclear fission and fusion.
CONTENT
NUCLEAR CHEMISTRY (RADIOACTIVITY)
Radioactivity is the spontaneous disintegration of nucleus resulting in emission of particles and rays in the process known as radioactive decay. The spontaneous continue till it forms a stable element.
Characteristic of radioactivity
I. Radioactive substance emits radiation continually and spontaneously.
II. It has high penetrating power.
III. It affects photographic plate
IV. It ionizes the gases through which it passes, causing fluorescence in certain substances e.g. ZnS
V. It involves release of energy.
TYPES OF RADIATION
Radioactive radiation consists of three main components of different penetrating power.
i. Alpha - α ii. Beta – β iii. Gamma rays – ϒ
|
|
Alpha - α |
Beta – β |
Gamma rays – ϒ |
|
Nature |
Helium nuclei, 42He |
Electrons, 0-1e |
Electromagnetic radiation |
|
Electrical charge |
+2 |
-1 |
No charge |
|
Mass |
4 units |
|
No mass |
|
Velocity |
About |
Varies (from 3-99% of the speed of light) |
Speed of light |
|
Relative penetration |
1 |
1000 |
10000 |
|
Absorber |
Thin paper |
Metal paper |
Large lead block |
|
Behavior in an electrostatic field |
Deflected slightly towards the negative plate in an electrostatic field. |
Deflected slightly towards the positive plate in an electrostatic field. |
Unaffected by an electrostatic field. |
X- RAY
X-rays are electromagnetic waves, like visible light, but with shorter wavelength. They are produced by allowing fast-moving electrons to bombard metal such as tungsten.
Properties of x-rays
I. It can penetrate easily through most solid substances which are opaque to visible light.
II. It is an electromagnetic waves with shorter wavelength.
Uses of x-ray
i. Used to study the arrangement of particles in crystal lattices and big organic molecules.
ii. Hard x-rays are used for destroying cancerous cells.
iii. Soft x-rays are used in medicine to photograph human body parts.
DETECTION OF
RADIATION
The common detectors or devices for detecting radiation are
I. Geiger-Muller counter
II. The scintillation counter
III. Photographic plate
IV. Diffusion cloud chamber
RADIOACTIVE
DISINTEGRATION
Radioactive is the spontaneous disintegration of the nucleus of an atom. During disintegration, a radioactive atom emits either an alpha particles, beta particles. Sometimes, gamma rays accompany the emission of these particles. The new element is called the daughter nucleus and this process is called the transmutation of an atom.
Alpha decay
It can be represented as follows:
Parent
nucleus
daughter nucleus alpha particle
Beta
decay
It can be represented as follows:
Parent
nucleus
daughter nucleus alpha particle
Nuclear
stability and radioactive decay
The nuclei of a radioactive element tend
to disintegrate spontaneously because they are unstable. The stability of an
atomic nucleus is related to the following factors:
I.
The neutron-proton ratio: for stable
atoms varies between unity for the lighter elements and a value of about 1.5
for those heavier elements with atomic numbers around 80, while those that less
than 1 or greater than 1.5 tend to be unstable and undergo radioactive decay.
II.
The half-life of the nucleus
III.
The nuclear force and binding energy.
Half-life
The half-life of a radioactive element is
the time taken for half of the total number of atoms in a given sample of the
element to decay.
T1/2
=
-2.303 Log (
Example
1.
The isotopes lead has a half life of 26.8
minutes. What amount of a 32g sample of lead remains after an hour?
Solution
The number of times it will
disintegration is =
(
Amount of lead sample remain (32g) X (0.212) = 6.784g
TYPES OF
RADIOACTIVITY
The transformation of one element to another during nuclear disintegration is known as Transmutation.
There are two types of radioactivity namely; natural radioactivity and artificial radioactivity.
I. Natural Radioactivity: This is the spontaneous disintegration of nucleus of naturally-occuring unstable atom e.g.
II. Artificial Radioactivity: This is the spontaneous disintegration of a nuclide by the bombardment of the stable nucleus of the atom with a high-speed particle or neutrons, protons and deuterium. This process is also known as Artificial Transmutation (the transforming of one element into another by means of particle bombardment) If the particle has sufficiently large energy, it combines with the stable nucleus to form a larger unstable nuclide which then disintegrates e.g.
NUCLEAR ENERGY
The particles in nucleus are collectively known as nucleons. The loss of mass i.e. differences between the sum of masses of its constituent particles (protons and neutrons) and the mass of the atom, is known as Mass Defect.
The defect of a nucleus is due to the conversion of some parts of the mass to energy. This mass-energy relationship can be explained using Einstein’s equation: E = mc2, where E is the energy in J, m is the loss in mass of the substance in kg, c is the velocity of light in ms-1.
Binding Energy is the energy released (evolved) during the formation of a nucleus from its constituents.
Nuclear Fission: is the process whereby a heavy nucleus is split into two or more lighter nuclei, with a release of energy and radiation. It produces neutrons for continuous reaction.
A chain reaction is a succession of nuclear fissions in which excess neutrons produced by fission cause further fission in other nuclei.
Nuclear Fusion: is the process whereby two or more light nuclei unite to form a heavier nucleus, with a release of energy and radiation.
Example
Q 1.Calculate the mass
defect and nuclear binding energy per nucleon of Li-7 (atomic mass = 7.016003 amu)
solution
Number of protons = 3
Number of neutrons = 7-3
= 4
Mass defect =
=
=
Nuclear binding energy
=
= 39.241 MeV
Total number of nucleons
= 7
Nuclear binding energy
per nucleon =
= 5.605 MeV / nucleon
Q 2—Atomic mass of 8O16 is
16.
Mass of one neutron =1.00893 amu; Mass of one
proton =1.00757 amu; Mass of one electron
=0.0005486 amu.
Calculate its mass defect & binding energy?
Solution
8O16 have 8p, 8n
& 8e
Mass of nucleus = Mass of 8p +mass of 8n
= (8×1.00757 )+ (8×1.00893)
= 8.06056+8.07144
= 16.1320 a.m.u
Mass of nucleus = Atomic Mass-Mass of 8e
= 16–8×0.0005486
= 16–0.0043888
= 15.9956112 amu
Mass defect (Δm)
= 16.1320–15.9956
(Δm) =
0.1364 amu Ans.
Binding energy ( B)
= Δm ×931 MeV
= 0.1364×931
B = 126.988 MeV
Q 3—Calculate Δm
& B. energy of 33As75. The mass of one
proton, one neutron & one electron & atomic mass of 33As75 is
1.0073 amu, 1.0087 amu& 0.0055 amu and 74.9216 amu
Solution
33As75 = 33e,
33p&42n
Mass of nucleus = mass of 33p + mass of 42n
= 33×1.0073+42×1.0087
= 33.2409 +42.3654
= 75.6063 amu
Mass of nucleus = Atomic Mass-Mass of 33e
= 74.9216 –33×0.00055
= 74.9216- 0.01815
= 74.90345 amu
Δm
= 75.6063–74.90345
Δm
= 0.70285 amu
B= Δm×931
MeV
= 0.70285×931
B = 654.35 MeV
USES OF RADIOACTIVE ISOTOPES
1.
In medicine, the radio isotopes are used to
cure cancerous tumour.
2.
It can also be used to trace tracks taken by
some substances in the human body.
3.
In agriculture, it is used to produce crops
with some properties to resists pest and control the growth of pest.
4.
In industry, are used to detect minute cracks
or leaks in solid structures.
5.
It is also used in long lasting luminescent
paint which can glow in the dark.
PRESENTATION
I. The teacher defines and states the characteristic of radioactivity.
II. The teacher states the types of radiation with their respective properties.
III. The students mention the types of radiation with their properties.
IV. The teacher explains nuclear fusion and fission.
V. The teacher leads the students in solving problems in radioactivity.
EVALUATION
The teacher evaluates the lessons by asking the following questions:-
1. Mention characteristics of radioactivity
2. State the types of radiation and their respective properties.
3. List some detector devices of radiation.
4. Solve problem involve nuclear chemistry
5. Differentiate between nuclear fission and fusion.
ASSIGNMENT
1.a Name the type of radiation that will:
I penetrate lead block
II be stopped by thin paper.
III Give the charge on each of the radiation mentioned in (1ai) above.
b. What term is used to describe each of the following nuclear processes.
I. Combination of two lighter nuclei to form a heavy nucleus.
II. Splitting of a heavy nucleus into two or more lighter nuclei.
III. Time required for one- half of the atom atoms of a radioactive substance to decay.
2a Balance the following nuclear reaction and identify A and B.
I.
b. Two radioactive element X andY have half life of 1200 seconds and3600 seconds respectively.
I. Which of the element is more stable?
II. Give a reason for your answer:
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