1) Nuclear chemistry involves radioactive decay and nuclear reactions like fission and fusion. Radioactive decay occurs when an unstable nucleus emits particles or energy to become more stable. 2) There are various types of radiation emitted in radioactive decay including alpha, beta, gamma, and positron emissions. The rate of decay is characterized by the half-life, which is the time for half of a radioactive sample to decay. 3) Nuclear reactions like fission and fusion can release large amounts of energy. Fission involves splitting heavy nuclei like uranium-235 and is used in nuclear power plants. Fusion combines light nuclei and occurs in stars but has not been achieved sustainably on Earth.

1. 1
CHAPTER 18
Nuclear
Chemistry
18.I Nuclear Stability &18.I Nuclear Stability &
Radioactive DecayRadioactive Decay pppp
I

2. 2
Black dots are
stable nuclides.
As A (atomic
mass) increases,
nº/p+
ratio
increases.

3. 3
Subatomic Particles
• Protons - plus charge
In the nucleus
• Neutrons - neutral
• Electrons - negative charge
Outside the nucleus

4. 4
Radiation
• Radiation comes from the nucleus of an atom.
• Unstable nucleus emits a particle or energy
α alpha
β beta
γ gamma

5. 5
He4
2
Types of RadiationTypes of Radiation
Alpha particle (α)
 helium nucleus paper2+
Beta particle (β-)
 electron
e0
-1 1-
lead
Positron (β+)
 positron e0
1+
1+
Gamma (γ)
 high-energy photon 0
concrete

6. 6
Radiation Protection
• Shielding
alpha – paper, clothing
beta – lab coat, gloves
gamma- lead, thick concrete
• Limit time exposed
• Keep distance from source

7. 7
Radiation Protection

8. 8
Nuclear DecayNuclear Decay
Alpha Emission
HeThU 4
2
234
90
238
92 +→
parent
nuclide
daughter
nuclide
alpha
particle
Atomic & Mass Numbers must balance!!

9. 9
Nuclear DecayNuclear Decay
Beta Emission
eXeI 0
-1
131
54
131
53 +→
electron
Positron Emission
eArK 0
1
38
18
38
19 ++→
positron

10. 10
Nuclear DecayNuclear Decay
 Electron Capture (of inner orbital electrons)
PdeAg 106
46
0
-1
106
47 →+
electronGamma Emission
 Usually follows other types of decay.
Transmutation
 One element becomes another.

11. 11

12. 12
Gamma radiation
No change in atomic or mass number
11
B 11
B + 0
γ
5 5 0
boron atom in a
high-energy state

13. 13

14. 14
Table 18.2 Types of Nuclear Processes p. 845

15. 15
Learning Check
Write the nuclear equation for the beta
emitter Cobalt-60. . .
60
Co 60
Ni + 0
e 27
28 -1

16. 16
Producing Radioactive Isotopes
Bombardment of atoms produces radioisotopes
= 60 = 60
59
Co + 1
n 56
Mn + 4
He
27 0 25 2
= 27 = 27
cobalt neutron manganese alpha
atom radioisotope particle

17. 17
Learning Check NR2
What radioactive isotope is produced in the
following bombardment of boron?
10
B + 4
He ? + 1
n
5 2 0

18. 18
Solution NR2
What radioactive isotope is produced in the
following bombardment of boron?
10
B + 4
He 13
N + 1
n
5 2 7 0
nitrogen
radioisotope

19. 19
Nuclear DecayNuclear Decay pppp
 Why nuclides decay…
 need stable ratio of neutrons to protons
HeThU 4
2
234
90
238
92 +→
eXeI 0
-1
131
54
131
53 +→
eArK 0
1
38
18
38
19 ++→
PdeAg 106
46
0
-1
106
47 →+
DECAY SERIES TRANSPARENCY

20. 2020
The decay series.The decay series.

21. 2121
18.2 Kinetics of Radioactive Decay18.2 Kinetics of Radioactive Decay
Rate of decay is a 1st order process, which is . . .Rate of decay is a 1st order process, which is . . .
ln(N/Nln(N/N00) = -kt) = -kt (memorize -- not on AP sheet)(memorize -- not on AP sheet)
NN00 = original number of nuclides at t = 0= original number of nuclides at t = 0
N = nuclidesN = nuclides remainingremaining at time tat time t
Half-life (tHalf-life (t1/21/2) = time for nuclides to reach half) = time for nuclides to reach half
their original value.their original value.
tt1/21/2 = 0.693/k= 0.693/k

22. 22
Half-lifeHalf-life
 Half-life (t1/2)
 Time required for half the atoms of a
radioactive nuclide to decay.
 Shorter half-life = less stable.

23. 23

24. 24
Examples of Half-Life
Isotope Half life
C-15 2.4 sec
Ra-224 3.6 days
Ra-223 12 days
I-125 60 days
C-14 5700 years
U-235 710 000 000 years

25. 25
Learning Check NR3
The half life of Iodine-123 is 13 hr. How much
of a 64 mg sample of Iodine-123 is left after
26 hours?

26. 26
Solution NR3
t1/2 = 13 hrs
26 hours = 2 x t1/2
Amount initial = 64mg
Amount remaining = 64 mg x 1/2 x 1/2
= 16 mg

27. 27
Half-lifeHalf-life
n
if mm )(2
1
=
mf: final mass
mi: initial mass
n: # of half-lives

28. 28
Half-lifeHalf-life pppp
 Fluorine-21 has a half-life of 5.0 seconds. If you start
with 25 g of fluorine-21, how many grams would remain
after 60.0 s?
GIVEN:
T1/2 = 5.0 s
mi = 25 g
mf = ?
total time = 60.0 s
n = 60.0s ÷ 5.0s =12
WORK:
mf = mi (1/2)n
mf = (25 g)(0.5)12
mf = 0.0061 g

29. 29 Kinetics of Nuclear Decay Problems pp
The rate constant for 99
43Tc = 1.16 x 10-1
/h
What is its half life? . . .
t1/2 = 0.693/k = 0.693/(1.16 x 10-1
/h) = 5.98 h
It will take 5.98 hours for a given sample of
technetium-99 to decrease to half the
original number of nuclides.

30. 30 Kinetics of Nuclear Decay Problems pp
 How long for 87.5% of a sample of cobalt-60How long for 87.5% of a sample of cobalt-60
to decay if tto decay if t1/21/2 = 5.26 years? Steps. . .= 5.26 years? Steps. . .
 What % is left? . . .What % is left? . . .
 12.5%12.5%
 How many half-lives to get to this percent?How many half-lives to get to this percent?
 3. So, your answer to the problem is . . .3. So, your answer to the problem is . . .
 3 x 5.26 = 15.8 years.3 x 5.26 = 15.8 years.

31. 31 Actual AP question: 1989 MC #68 pp
If k = 0.023 min-1
how much of X was
originally present if have 40. g after 60 min.?
Your answer is . . .
160. g. Solution . . .
t1/2 = 0.693/k = 0.693/0.023 min-1
= 30 min.
60 minutes is 2 half-lives so going backwards
40. g to 80. g to 160. g.

32. 32 18.3 Nuclear Transformations
Transmutation - change of one element into
another.
Particle and linear accelerators are used to
synthesize new elements (currently up to
element number 119).
Difficult to characterize the chemical
properties because with some only a few
atoms are formed with very short half-lives.

33. 3333
A representation of a Geiger-Müller counter.A representation of a Geiger-Müller counter.

34. 34
18.4 Detection & Uses of Radioactivity
Half-life measurements of radioactive
elements are used to determine the age of
an object
Decay rate indicates amount of
radioactive material
EX: 14
C - up to 40,000 years
238
U and 40
K - over 300,000 years

35. 35
Synthetic ElementsSynthetic Elements
 Transuranium Elements
 elements with atomic #s above 92
 synthetically produced in nuclear reactors
and accelerators
 most decay very rapidly
PuHeU 242
94
4
2
238
92 →+

36. 36 Carbon-14 DatingCarbon-14 Dating
You will have a test question like this!You will have a test question like this! pppp
 An ancient fire in an African cave has aAn ancient fire in an African cave has a 1414
CC
decay rate of 3.1 cpm (cts per minute). Ifdecay rate of 3.1 cpm (cts per minute). If
fresh wood has 13.6 cpm how old is thefresh wood has 13.6 cpm how old is the
campfire if tcampfire if t1/21/2 = 5730 years? Steps . . .= 5730 years? Steps . . .
 Decay rates are directly proportional toDecay rates are directly proportional to
nuclides so their ratio =nuclides so their ratio = N/NN/N00 What is theWhat is the
numerical ratio? Your answer . . .numerical ratio? Your answer . . .
 3.1 cpm/13.6 cpm =3.1 cpm/13.6 cpm = 0.230.23
 Use the two previous equations to solveUse the two previous equations to solve
(next slide).(next slide).

37. 37 Carbon-14 Dating
You will have a test question like this! pp
Ancient fire 14
C decay rate 3.1 cpm, fresh
wood 13.6 cpm how old if t1/2 = 5730 yrs?
3.1 cpm/13.6 cpm = 0.23 = N/N0
ln(N/N0) = -kt and t1/2 = 0.693/k
You want to solve for t (vs. t1/2) so use t1/2 to
get k then plug into the 1st equation and
solve for t. Your answer is . . .
The campfire is 12 000 years old.
ln(N/N0) = ln(0.23) = -(0.693/5730)t

38. 38 Carbon-14 Dating
You will have another test question like this! pp
A rock has ratio of Pb-206 to U-238 of 0.115.
How old is it if t1/2 of U-238 = 4.5 x 109
yrs?
Strategy: figure out N/N0 of U-238, then use
the 2 previous equations to get . . .
7.1 x 108
years. Calculations . . .
Pb/U = 115/1000 so N0 U238 = 1115, N = 1000
ln(1000/1115) = -(0.693/4.5 x 109
)t

39. 39
Nuclear MedicineNuclear Medicine
Radioisotope Tracers
 absorbed by specific organs and used
to diagnose diseases
Radiation Treatment
 larger doses are used
to kill cancerous cells
in targeted organs
 internal or external
radiation source
Radiation treatment using
γ-rays from cobalt-60.

40. 40
Other UsesOther Uses
Food Irradiation
 γ radiation is used to kill bacteria
Radioactive Tracers
 explore chemical pathways
 trace water flow
 study plant growth, photosynthesis
Consumer Products
 ionizing smoke detectors - 241
Am

41. 41
Radioisotopes Used As Tracers

42. 42
18.5 Thermodynamic Stability of the Nucleus
 Mass Defect - difference from mass of anMass Defect - difference from mass of an
atomatom & the mass of its individual particles.& the mass of its individual particles.
4.00260 amu 4.03298 amu

43. 43
Nuclear Binding EnergyNuclear Binding Energy
Energy released when a nucleus is
formed from nucleons.
High binding energy = stable nucleus.
E = mc2
E: energy (J)
m: mass defect (kg)
c: speed of light
(3.00 x 108
m/s)

44. 44 Nuclear Binding EnergyNuclear Binding Energy
Unstable nuclides - radioactive & undergo radioactive
decay.
Elements with intermediate atomic masses (e.g., Fe) have
greatest binding energy, so are the most stable.

45. 45
18.6 Nuclear Fission and Nuclear Fusion
Fission -
splitting
Fusion -
Combining
Both produce
more stable
nuclides so
they are
exothermic
processes

46. 46
A. Nuclear FissionA. Nuclear Fission
Splitting a nucleus into two or more smaller
nuclei
1 g of 235
U =
3 tons of coal
U235
92

47. 47
Nuclear Fission
Fission
large nuclei break up
235
U + 1
n 139
Ba + 94
Kr + 3 1
n +
92 0 56 36 0
Energy

48. 48
Nuclear PowerNuclear Power
Fission Reactors Cooling
Tower

49. 4949
Schematic of the reactor core.Schematic of the reactor core.

50. 50
Nuclear PowerNuclear Power
Fission Reactors

51. 51
FissionFission
 chain reaction - self-propagating reaction
 critical mass -
mass required
to sustain a
chain reaction

52. 52

53. 53
Nuclear FusionNuclear Fusion
 combining of two nuclei to form one nucleus of
larger mass
 thermonuclear reaction – requires temp of
40,000,000 K to sustain
 1 g of fusion fuel =
20 tons of coal (vs. 3 in
fission)
 occurs naturally in
stars
HH 3
1
2
1 +

54. 54
Nuclear Fusion
Fusion
small nuclei combine
2
H + 3
H 4
He + 1
n +
1 1 2 0
Occurs in the sun and other stars
Energy

55. 55
Nuclear PowerNuclear Power
Fusion Reactors (not yet sustainable)

56. 56
Nuclear PowerNuclear Power
Fusion Reactors (not yet sustainable)
Tokomak Fusion Test Reactor
Princeton University
National Spherical
Torus Experiment

57. 57
Fission vs. FusionFission vs. Fusion pp
 235
U is limited
 danger of meltdown
 toxic waste
 thermal pollution
 fuel is abundant
 no danger of meltdown
 no toxic waste
 not yet sustainable
F
I
S
S
I
O
N
F
U
S
I
O
N

58. 58
Learning Check NR4
Indicate if each of the following are
(1) Fission (2) fusion
A. Nucleus splits
B. Large amounts of energy released
C. Small nuclei form larger nuclei
D. Hydrogen nuclei react
Energy

59. 59
Solution NR4
Indicate if each of the following are
(1) Fission (2) fusion
A. 1 Nucleus splits
B. 1 + 2 Large amounts of energy released
C. 2 Small nuclei form larger nuclei
D. 2 Hydrogen nuclei react

60. 60
E. Nuclear WeaponsE. Nuclear Weapons
Atomic Bomb
 chemical explosion is used to form a
critical mass of 235
U or 239
Pu
 fission develops into an uncontrolled
chain reaction
Hydrogen Bomb
 chemical explosion → fission → fusion
 fusion increases the fission rate
 more powerful than the atomic bomb

61. 61
18.7 Effects of Radiation pp
Somatic - damage to the organism
causing sickness or death.
Genetic - damage to the genetic
machinery causing birth defects.

62. 62
Factors for Biological Effects of Radiation pp
 Energy - higher energy content (rads) causes
more damage.
 Penetrating Ability - γ > β- > α
 Ionizing Ability - α > β- > γ (eating an α-particle
producer like Pu is very deadly)
 Chemical Properties
• Kr-85 is chemically inert, passes through
quickly
• Sr-90 collects in bone and stays a long time
in the body.

63. 63

64. 64
Radioactive particlesRadioactive particles
and rays vary greatly inand rays vary greatly in
penetrating power.penetrating power.

65. 65

66. 6666
Diagram forDiagram for
the tentativethe tentative
plan for deepplan for deep
undergroundunderground
isolation ofisolation of
nuclear wastenuclear waste..