1. Chapter 25
Nuclear Chemistry

2. Nuclear Radiation Nuclear chem
the study of the structure of atomic nuclei and the changes they undergo.
No e- / orbitals
No e- sharing or transferring
No cpds formed
No bondings

3. The Discovery of Radioactivity
In 1895, Roentgen found that invisible rays were emitted when e- bombarded the surface of certain materials.
they caused photographic plates to darken.
named these invisible high-energy emissions X rays.

4. The Discovery of Radioactivity
At that time, French physicist Becquerel was studying minerals that
emit light after being exposed to sunlight (phosphorescence).
Building on Roentgen’s work, Becquerel wanted to determine whether phosphorescent minerals also emitted X rays.

5. The Discovery of Radioactivity
Becquerel accidentally discovered that phosphorescent U salts – even when not exposed to light – produced spontaneous emissions that darkened photographic plates.

6. The Discovery of Radioactivity
Marie Curie (1867–1934) and her husband Pierre (1859–1906) took Becquerel’s mineral sample and isolated the components emitting the rays.

7. The Discovery of Radioactivity
Conclusion:
the darkening of the photographic plates was due to rays emitted specifically from the U atoms in the mineral sample.
named the process by which materials give off such rays radioactivity;
the rays and particles emitted by a radioactive source are called radiation.

8. Types of Radiation Isotopes
are atoms of the same element that have different #s of n0.
Radioisotopes
Isotopes of atoms with unstable nuclei ready to emit radiations.
unstable nuclei is due to big diffce in the # of
p+ and n e.g. U has 92 p+ and over 140 n0
Mg has 12 p+ and 12 n0 (stable)

9. Quick write
What kind of atoms are radioactive?

10. Types of Radiation radioactive decay
A process that unstable nuclei emit radiation to attain more stable atomic configns.
During radioactive decay, unstable atoms lose energy by emitting 1 of several types of radiation.

11. Types of Radiation 3 common types of radiation alpha (α) beta (β)
gamma (γ)

12. Moderate (4 mm body tissue) Very high
Property
Alpha (α)
Beta (β)
Gamma (ɣ)
composition
Alpha particles
Beta particles
electromagnetic radiations (waves)
description
4α (He nucleus)
0β (electron)
0γ (photon)
charge 2+ 1−
Common source
Ra-266
C-14
Co-60
Mass (a.m.u.) 4 1
Penetrating power
Low (0.05 mm body tissue)
Moderate (4 mm body tissue)
Very high
shielding
Paper, clothing
metal foil
lead or concrete 2 -1
1837

13. Quick Write
What are α particles? How many p+, n0 and e- does each particle carry?

14. Radioactive Decay Radioactive Decay
unstable nuclei loses energy by emitting radiation: ‘particles’ or ‘energy (non-particles)’.
become lighter
Natural (not human initiated; can’t stop or slow down)
not requiring any energy input.
Spontaneous

16. Quick Write
What are the areas that α decay and β decay have in common? (4 bullet pts)

17. Radioactive Decay

18. Half-life
Half-life
Time required for one half of the nuclei of a radioisotope sample to decay.
e.g. U → Th + α-particle
Each radioisotope has a characteristic t 1/2

19. Half-life
Half-life
Time required for one half of the nuclei of a radioisotope sample to decay.
e.g. U → Th + α-particle
238U → 234Th He
Each radioisotope has a characteristic t 1/2 92 90 2

20. Half-life (t ½) Isotope Half life Radiation emitted C -14
5.73 x 10 3 years β
Rn – 222
3.8 days α
U-238
4.46 x 109 years
Th – 230
7.54 x 104 years
α, γ

24. Effect of an Electric Field (1)
What radiations are deflected toward the -ve plate? Why?
What radiations are deflected toward the +vely plate? Why?

25. Quick Write
What is radioactive decay? (5 bullet points)

26. Quick Write
Describe and explain the paths of α, β, and γ radiation under the influence of electric field?

27. Effect of an Electric Field (2)
The +vely charged α particles are deflected towards the -ve plate.
The –vely charged β particles are deflected towards the +ve plate.
the neutral γ radiation travels in a straight line.

28. Quick Write
What are β particles? Do they carry any charges?

29. Quick Write
What is γ radiation? What charge does it carry?

30. Effect of an Electric Field (2)
β particles are deflected towards the +ve plate.
β particles undergo greater deflection because →less mass.

31. Effect of an Electric Field (3)
γ ray, (no electrical charge), are not deflected.

32. Types of Radiation- α radiation
An α particle has the same composition as a He nucleus—2 p+ and 2 n —
2+ due to the presence of the 2 p+.

33. Types of Radiation- α radiation
α radiation—a stream of α particles.
Ra-226, (88 p+ and 138 n0), undergoes α decay by emitting an α particle.

34. Types of Radiation- α radiation
After the decay, the resulting atom has an atomic # of 86, a mass # of 222.
The new radiosiotope is Rn-222.

35. Types of Radiation The particles involved are balanced.
i.e. the sum of the mass #s (superscripts) = the sum of the atomic #s (subscripts) on each side of the arrow.

36. Types of Radiation
Because of their mass and charge, α particles are relatively slow-moving compared with other …
Thus, α particles are not very penetrating—a single sheet of paper stops.

37. Types of Radiation—β Radiation
A β particle is a very-fast moving e- that has been emitted from a n0 of an unstable nucleus.
β particles are represented by the symbol The ‘0’ superscript indicates the insignificant mass of an e- in comparison with the mass of a nucleus.

39. Types of Radiation—β Radiation
The –1 subscript denotes the -ve charge of the particle.
β radiation consists of a stream of fast-moving e-.

40. Types of Radiation
An example of the β decay process is the decay of I-131 into Xe-131 by β-particle emission.

41. Types of Radiation-- β Radiation
The mass # of the product nucleus is the same as that of the original nucleus (both 131), but its atomic # has increased by 1 (54 instead of 53).

42. Types of Radiation-- β Radiation
This change in atomic #, and thus, change in identity, occurs because the e- emitted during the β decay has been removed from a n0, leaving behind a p+.

43. Types of Radiation—β Radiation
fast-moving e- formed by decomposition of a n0 in an atom.
Quick write: why the mass # remain 14 while there is an additional p+?

44. Types of Radiation
Because β particles are both lightweight and fast moving, they have greater penetrating power than α particles.
A thin metal foil is required to stop β particles.

45. Types of Radiation
γ rays are high-energy (short wavelength) electromagnetic radiation.
They are denoted by the symbol .
Both the subscript and superscript are ‘0’.

46. Types of Radiation
Thus, the emission of γ rays does not change the atomic # or mass # of a nucleus.
γ rays almost always accompany α and β radiation, as they account for most of the energy loss that occurs as a nucleus decays.

47. Types of Radiation e.g. γ rays accompany the α-decay rxn of U-238.
The 2 in front of the γ symbol indicates that 2 γ rays of different frequencies are emitted.
Because γ rays have no effect on mass # or atomic #, it is customary to omit them from nuclear eqns.

48. Radioactive Decay
Of all the known isotopes, only about 17% are stable and don’t decay spontaneously.

49. Beta Decay
A radioisotope that lies above the band of stability is unstable because it has too many n relative to its # of p+.
e.g. unstable has a n0 / p+ ratio of 1.33 : 1, whereas stable elements of similar mass, such as
and , have n0 / p+ ratios ≈1:1

50. Beta Decay
It is not surprising then that undergoes beta decay, as this type of decay decreases the # of n0 in the nucleus.
Note that the atomic # of the product nucleus, , has increased by 1.
The N-14 atom now has a stable n0 / p+ ratio of 1 : 1.

51. Beta Decay
Thus, β emission has the effect of increasing the stability of a n0 -rich atom by lowering its n0 / p+ ratio.
The resulting atom is closer to, if not within, the band of stability.

52. Alpha Decay
All nuclei with more than 83 p+ are radioactive and decay spontaneously.
Both the # of n0 and the # of p+ must be reduced in order to make these radioisotopes stable.
These very heavy nuclei often decay by emitting α particles.

53. Alpha Decay e.g. , Po-210 spontaneously decays by α emission.
The atomic # of decreases by 2 and the mass # decreases by 4 as the nucleus decays into

55. Nuclear Fission Nuclear Fission
Nuclei of certain isotopes (e.g U-238) are bombarded with n0 split into smaller fragments of similar sizes.
Unleash enormous amt of energy e.g. 1 kg of U- 235 (explosion of tons of dynamite)

57. Nuclear Fission

58. Nuclear Fission

59. Nuclear Fission In a chain rxn
some of the n0 produced react with other fissionable atoms
producing more n0 which react with still more fissionable atoms.

61. Nuclear Fission
A Nuclear Power Plant

63. Process of Enrichment

64. Nuclear Fission Neutron Moderation
a process that slows down n0 so the reactor fuel (U-235 or Po-239) captures them to continue the chain rxn.

65. Nuclear Fission Neutron Absorption
a process that decreases the # of slow-moving n0.
water slow down the n0 in the reactor
Control rods—made of a material such a Cd, or B, are used to absorb n0.

67. Nuclear Fission Nuclear Fission
Nuclei of certain isotopes are bombarded with neutrons
split into smaller fragments of similar sizes.
Unleash enormous amt of energy
e.g. 1 kg of U- 235 ( explosion of tons of dynamite)

68. Nuclear Fission Uncontrolled fission
Total energy release is instantaneous (fraction of a second);
uncontrolled chain rxn—atomic bomb;
Controlled fission
so energy is released more slowly (nuclear power)

70. Controled/uncontroled fission

71. Fission and Fusion of Atomic Nuclei
The sun is not actually burning (combustion).
would have burned out approximately 2000 years after it was formed.

72. Nuclear Fusion Nuclear Fusion
Occur when small nuclei combine to produce a nucleus of greater mass
H nuclei (p+) fuse to make He nuclei

73. Nuclear Fusion much more energy than fission rxn
occur at very high temp (40, 000, 000 ° C)
good energy source--- cheap fuel;
readily available; controlled

74. Nuclear Fusion
problems; high temp to initiate? --- needs an atomic bomb to trigger a nuclear fusion rxn…
**** the energy release per g of the material is much larger in nuclear fusion or fission rxns than in chem rxns.
change in mass (calculated by E = mc2 ) is small but significant in nuclear rxns.

75. Quick-write
25.3
How do fission rxns and fusion rxns differ?

76. Nuclear Fusion
Fusion
occurs when nuclei combine to produce a nucleus of greater mass.
In solar fusion, H nuclei (p+) fuse to make He nuclei and 2 positrons.

77. Nuclear Fusion

78. Nuclear Fusion Fusion rxns small nuclei combine,
release much more energy than fission rxns (large nuclei split).

79. The potential fuels are inexpensive and readily available.
Nuclear Fusion
25.3
The use of controlled fusion as an energy source on Earth is appealing.
The potential fuels are inexpensive and readily available.
The problems with fusion
in achieving the high temperatures necessary to start the rxn and
in containing the rxn once it has started.

80. Applications of Nuclear Power
Cancer treatment (radiation therapy)
high-energy X-rays are directed at a person’s body to kill cancer cells
X-rays, MRI, CT scan
e.g. dentist’s office “radiation therapy”
Nuclear medicine
Uses radionuclides in the diagnosis of disease
Relies on process of radioactive decay
Wilhelm Roentgen, 1895– x-rayed his wife’s hand

81. CST example 1
A 2-cm thick piece of cardboard placed over a radiation source would be most effect in protecting against which type of radiation?
A alpha
B beta
C gamma
D x-ray

82. Which equation correctly represents the alpha decay of polonium-214?
CST problem 2
Which equation correctly represents the alpha decay of polonium-214?
A 214 Po
84 85

83. The End