Introduction
Nuclear chemistry is the branch of chemistry that deals with changes in the nucleus of an atom. These changes involve the emission of particles or radiation and are known as nuclear reactions. Unlike ordinary chemical reactions, nuclear reactions involve the nucleus and may result in the formation of new elements.
THĺE NUCLEUS AND NUCLEAR STABILITY
The nucleus of an atom contains:
Protons (positively charged)
Neutrons (neutral)
The stability of a nucleus depends on the neutron–proton ratio. Unstable nuclei undergo radioactive decay to become more stable.
RADIOACTIVITY
Radioactivity is the spontaneous disintegration of unstable atomic nuclei with the emission of radiation.
Types of Radioactive Radiation
1. Characteristics of Alpha (α) particles
i. they are positively charged particles that resembles the helium nucleus
ii. they are deflected towards the negative plate
iii. They have Low penetrating power (Can be stopped by paper or skin)
iv. They have high ionizing power
Example:
²³⁸₉₂U → ²³⁴₉₀Th + ⁴₂He
2. Beta (β) particles
i. Fast-moving electrons
ii. Negatively charged
iii. Moderate penetrating power (Stopped by thin aluminum sheet)
Example:
¹⁴₆C → ¹⁴₇N + β⁻
3. Gamma (γ) rays
i. High-energy electromagnetic radiation
ii. They have No mass and no charge.
iii. They have Very high penetrating power ( Stopped by thick lead or concrete)
NUCLEAR EQUATIONS
In nuclear reactions:
Mass number is conserved
Atomic number is conserved
HALF-LIFE
Half-life is the time taken for half the number of radioactive atoms in a substance to decay.
Example:
If a substance has a half-life of 10 years:
After 10 years → ½ remains
After 20 years → ¼ remains
TYPES OF NUCLEAR REACTIONS
1. Nuclear Fission
Nuclear fission is the splitting of a heavy nucleus into two lighter nuclei with the release of a large amount of energy and radiation
Example:
²³⁵₉₂U + ¹₀n → ¹⁴¹₅₆Ba + ⁹²₃₆Kr + 3¹₀n + energy
Uses of fission:
i. Nuclear power plants for power generation
ii. Atomic bombs
2. Nuclear Fusion
Nuclear fusion is the combination of two light nuclei to form a heavier nucleus with the release of energy and radiation.
Example:
²₁H + ³₁H → ⁴₂He + energy
Uses of fusion:
It is a source of energy in the sun and stars
It used for making Hydrogen bomb
DIFFERENCE BETWEEN FISSION AND FUSION
| Fission | Fusion |
|---|---|
| Splitting of heavy nucleus | Combination of light nuclei |
| Produces radioactive waste | Produces little waste |
| Used in nuclear reactors | Occurs in the sun |
| Lower temperature required | Extremely high temperature required |
ARTIFICIAL TRANSMUTATION
Artificial transmutation is the conversion of one element into another by bombarding the nucleus with particles. Thats is, causing radioactivity to occur artificially
Example:
¹⁴₇N + ⁴₂He → ¹⁷₈O + ¹₁H
USES OF RADIOISOTOPES
In Medicin Cancer treatment (radiotherapy)
i. Tracers in diagnosis
ii. Sterilization of medical equipment
In Industry
i. Detecting cracks in metals
ii. Thickness control in manufacturing Packaging materials
In Agriculture
i. Food preservation
ii. Pest control (radiations are used to destroy the reproductive cells of male insect)
In Archaeology
i. Carbon-14 dating to determine age of fossils
HAZARDS OF NUCLEAR RADIATION
Causes cancer
Damages living tissues
Leads to genetic mutations
Can cause radiation sickness
Safety Measures
Use of lead materials for shielding
Wearing protective clothing
Proper disposal of radioactive waste
ADVANTAGES OF NUCLEAR ENERGY
Produces large amount of energy
Requires small amount of fuel
No greenhouse gas emission during operation
DISADVANTAGES OF NUCLEAR ENERGY
Radioactive waste disposal problem
Risk of nuclear accidents
High cost of setup and maintenance
SUMMARY (AT A GLANCE)
Nuclear chemistry deals with changes in atomic nuclei
Radioactivity involves alpha, beta, and gamma radiation
Half-life measures rate of decay
Nuclear reactions include fission and fusion
Nuclear energy has many uses but also serious hazards
OBJECTIVE QUESTIONS
1. Nuclear chemistry mainly deals with changes in the
A. electron cloud
B. outer shell electrons
C. nucleus of an atom
D. valence electrons
2. Which of the following particles has the greatest penetrating power?
A. Alpha particles
B. Beta particles
C. Gamma rays
D. Protons
3. An alpha particle consists of
A. one proton
B. one electron
C. two protons and two neutrons
D. two electrons and two protons
4. Which radiation is deflected most by an electric field?
A. Alpha rays
B. Beta rays
C. Gamma rays
D. Neutron rays
5. Radioactivity is best described as
A. a chemical change
B. a physical change
C. spontaneous nuclear disintegration
D. a reversible reaction
6. The half-life of a radioactive substance is the time taken for
A. all atoms to decay
B. half of the atoms to decay
C. the activity to stop
D. the mass to double
7. If a radioactive substance has a half-life of 5 days, how long will it take for three-quarters of it to decay?
A. 5 days
B. 10 days
C. 15 days
D. 20 days
8. Which of the following is conserved in a nuclear reaction?
A. Number of electrons
B. Chemical properties
C. Atomic number and mass number
D. Physical state
9. The splitting of a heavy nucleus into lighter nuclei is known as
A. nuclear fusion
B. radioactive decay
C. nuclear fission
D. artificial transmutation
10. Nuclear fusion occurs mainly in
A. nuclear reactors
B. atomic bombs
C. the sun and stars
D. radioactive waste
11. One major difference between nuclear reactions and chemical reactions is that nuclear reactions
A. involve electrons
B. involve energy changes only
C. involve the nucleus
D. are reversible
12. Which of the following is used as a moderator in a nuclear reactor?
A. Graphite
B. Uranium
C. Plutonium
D. Lead
13. Carbon-14 is mainly used for
A. treating cancer
B. food preservation
C. determining the age of fossils
D. generating electricity
14. Which radiation is stopped by a sheet of paper?
A. Gamma rays
B. Beta particles
C. Alpha particles
D. Neutron rays
15. In nuclear fission, energy is released because
A. mass is conserved
B. mass is converted into energy
C. electrons are transferred
D. atoms are rearranged
16. Artificial transmutation involves
A. natural decay of elements
B. fusion of light nuclei
C. conversion of one element to another by bombardment
D. spontaneous disintegration
17. Which of the following is a hazard of nuclear radiation?
A. Increase in melting point
B. Formation of alloys
C. Genetic mutation
D. Improved conductivity
18. The SI unit of radioactivity is
A. joule
B. becquerel
C. watt
D. volt
19. Which statement about gamma rays is correct?
A. They are negatively charged
B. They have mass
C. They are electromagnetic waves
D. They are easily stopped by paper
20. Which of the following is an advantage of nuclear energy?
A. Produces smoke
B. Requires large fuel quantity
C. Produces large energy from small fuel
D. Produces no waste
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