Post on 14-Apr-2018
5/29/2018
1
11Chemistry: OpenStax
Ch. 21: Nuclear Chemistry
Nuclear chemistry provides the basis for many useful diagnostic and therapeutic methods
in medicine, such as these positron emission tomography (PET) scans. The PET/computed
tomography scan on the left shows muscle activity. The brain scans in the center show
chemical differences in dopamine signaling in the brains of addicts and nonaddicts.
The images on the right show an oncological application of PET scans to identify
lymph node metastasis.
22
Creative Commons License
� Images and tables in this file have been used from the following sources:
� OpenStax: Creative Commons Attribution License 4.0.
� ChemWiki (CC BY-NC-SA 3.0): Unless otherwise noted, the StatWiki is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License. Permissions beyond the scope of this license may be available at copyright@ucdavis.edu.
� Principles of General Chemistry (CC BY-NC-SA 3.0): http://2012books.lardbucket.org/pdfs/principles-of-general-chemistry-v1.0.pdf
� Nuclear (NOT Nucular) chemistry involves changes
in the nuclear composition (protons and neutrons) of
atoms that are radioactive.
� Nuclear chemistry can be used:
� to generate electricity
� 2 million kg of coal or 50 kg of uranium-235 can provide
electricity for a city of 1 million people
� for radiocarbon dating (e.g., determining the age of a
mummy or a meteorite)
� for medical diagnosis, treatment, and imaging (PET
scans, brain scans, x-rays)
� to create new elements 3
Nuclear Reactions
4
Spontaneous emission of particles or electromagnetic radiation is
known as radioactivity.
Atomic notation and terms:
Atomic number (Z) = number of protons
Mass number (A) = number of protons and neutrons in a
specific isotope (or nuclide) of an element
Protons and neutrons are collectively called nucleons.
Radioactive isotopes are often called nuclides.
How many neutrons are in each nuclide below?
Nuclei and Nuclear Reactions
5
How do we know whether an isotope is
stable? Which radioisotopes will
spontaneously decay?
1) Nuclei containing a magic number of
protons and/or neutrons are stable.
• The numbers 2, 8, 20, 50, 82, and 126
are called magic numbers.
2) Even numbers of protons and neutrons
tend to be stable.
3) All isotopes of the elements with
atomic numbers > 83 are radioactive.
4) All isotopes of technetium (Tc, Z = 43)
and promethium (Pm, Z = 61) are
radioactive.
21.1 Nuclear Structure and Stability
CC-BY-NA-3.0: http://chemwiki.ucdavis.edu/Wikitexts/Prince_Georges_Community_College/General_Chemistry_for_Engineering/Unit_7%3A_Nuclear_Chemistry/Chapter_18%3A_Nuclear_Chemistry/Chapter_18.1%3A_The_Components_of_the_Nucleus
6
Band of Stability
CC-BY-NA-3.0: http://chemwiki.ucdavis.edu/Wikitexts/Prince_Georges_Community_College/General_Chemistry_for_Engineering/Unit_7%3A_Nuclear_Chemistry/Chapter_18%3A_Nuclear_Chemistry/Chapter_18.1%3A_The_Components_of_the_Nucleus
5/29/2018
2
The three general classes of radioactive nuclei are characterized by a different
decay process or set of processes:
N/Z too high. The nuclei on the upper left side of the band of stable nuclei in
Figure 18.1.2 have a neutron-to-proton ratio that is too high to give a stable
nucleus. These nuclei decay by a beta decay – converting a neutron to a proton,
thereby decreasing the neutron-to-proton ratio.
N/Z too low. Nuclei on the lower right side of the band of stable nuclei have a
neutron-to-proton ratio that is too low to give a stable nucleus. These nuclei
decay by positron emission or electron capture – converting a proton to a
neutron, thereby increasing the neutron-to-proton ratio.
Heavy nuclei. With very few exceptions, heavy nuclei (those with A ≥ 200) are
intrinsically unstable regardless of the neutron-to-proton ratio, and all nuclei
with Z > 83 are unstable. Such nuclei tend to decay by emitting an α particle
which decreases the number of protons and neutrons in the original nucleus by
2. The net result of alpha emission is an increase in the neutron-to-proton ratio.
Predicting Types of Decay
8
Figure 21.4: Symbols for subatomic particles
21.2 Nuclear Particles
Penetrating Ability of Particles
Figure 21.33
10
• Radioactive decay/emission: an unstable nuclide emits a
particle or energy.
• Parent nuclide � daughter nuclide + radiation
• Fission: bombarding an isotope with a neutron to break it apart
into lighter isotopes.
• Fusion: light isotopes collide to form heavier isotopes (only up
to Fe can be done naturally in the universe)
• Transmutation: atoms are bombarded by high energy particles
to create new elements/isotopes.
• 14N + 4He � 17O + 1H
+
Types of Nuclear Reactions
11
In balancing a nuclear reaction, we balance the total of all
atomic numbers and total of all mass numbers for the
products and reactants (conservation of protons and
neutrons).
Example 21.4
Mass number:
Atomic number:
+
212 208 + 4 = 212
84 82 + 2 = 84
21.3 Radioactive Decay
� Alpha decay - heavy radioisotopes tend to emit alpha particles (A dec. by 4, Z dec by 2)
� ������ → ��
____
12
Alpha Decay (or Emission)
http://underground.physics.berkeley.edu/SNO+.html
5/29/2018
3
� Beta decay - neutron is converted to a proton and an electron (A is same, Z inc. by 1)
� � ����� → ���
� ____
13
Beta Decay (or Emission)
http://www.ck12.org/user:chjpdgnoyxjkx3naagnkzs5vcmc./book/Chemical-Equations-and-Balancing-The-Equations/section/24.2/
14
Gamma Decay (or Emission)
� Gamma – γ: energy with no mass or charge; the most
penetrating radiation (A and Z remain the same)
� This often occurs in conjunction with alpha or beta
decay.
� ������∗ � → ���
� ��� _____
http://2012books.lardbucket.org/books/principles-of-general-chemistry-v1.0/s24-nuclear-chemistry.html
� Positron decay – proton is converted to a neutron and a positron (A is same, Z dec. by 1)
� A positron is the antiparticle of the electron
� ���� ���
� → ���
� ����� → ���
� _____
15
Positron Decay (or Emission)
http://2012books.lardbucket.org/books/principles-of-general-chemistry-v1.0/s24-nuclear-chemistry.html
� Electron Capture – electron combines with a
proton to form a neutron (A is same, Z dec by 1)
� Same result as positron decay; opposite of beta decay
� ���� ���
� → _____
16
Electron Capture
http://2012books.lardbucket.org/books/principles-of-general-chemistry-v1.0/s24-nuclear-chemistry.html
� Write balanced equations for the following:
� Alpha decay of 214Bi
� Alpha decay of curium-242
� Beta decay of 239U
� Beta emission of magnesium-28
� Positron emission of 207Po
� Electron capture of 197Hg
� Electron capture of gallium-67
17
Group Work - Practice
Answers:
� 210Tl
� 238Pu
� 239Np
� 28Al
� 207Bi
� 197Au
� 67Zn
18
Uranium Series of Decay
CC-BY-NA-3.0: http://chemwiki.ucdavis.edu/Wikitexts/Heartland_Community_College/HCC%3A_Chem_162/21%3A_Nuclear_Chemistry/21.1%3A_Radioactivity
5/29/2018
4
Natural radioactive decay:
Nuclear Transmutation:
Nuclear fission:
19
Determining Products of Reactions
20
Band of Stability
CC-BY-NA-3.0: http://chemwiki.ucdavis.edu/Wikitexts/Prince_Georges_Community_College/General_Chemistry_for_Engineering/Unit_7%3A_Nuclear_Chemistry/Chapter_18%3A_Nuclear_Chemistry/Chapter_18.1%3A_The_Components_of_the_Nucleus
Four New Elements!
https://www.sciencenews.org/article/four-elements-earn-permanent-seats-periodic-table
110: Darmstadtium (Ds)111: Roentgenium (Rg)112: Copernicium (Cn)113: Nihonium (Nh)114: Flerovium (Fl)115: Moscovium (Mc)116: Livermorium (Lv)117: Tennesine (Ts) 118: Oganesson (Og)
Nuclide Type of Emission Half-life
Part of Body
Studied
Fluorine-18 Positron emission 1.83 hours PET studies of
heart, brain
Technetium-99m Gamma 6.01 hours Various organs,
bones
Thallium-201 Electron capture 3.05 days Heart
Iodine-131 Beta 8.0 days Thyroid
Phosphorus-32 Beta 14.3 days Tumors in various
organs
Iron-59 Beta 44.5 days Blood, spleen
Radioactivity in Medicine
Source Dose
5-hour plane ride 2.5 mrem/trip
Cosmic radiation 27 mrem/year
Natural radionuclides in body 35 mrem/year
Chest x-ray 8 mrem
Dental x-ray 30 – 80 mrem (pano vs bitewings)
Thallium heart scan 800 mrem
Building materials 3.5 mrem/year
Luminous watches 0.04 – 0.10 mrem/year
Tobacco products (30
cigarettes/day)
16,000 mrem/year
Exposure by Source – U.S.Dose (rem) Symptoms/Effects
< 5 No observable effect
5-20 Possible chromosomal damage
20-100 Decreased white blood cell count; possible increased cancer risk
50-100 Temporary sterility in men (up to a year)
100-200 Mild radiation sickness, vomiting, diarrhea, fatigue; immune system
suppressed; bone growth in children retarded
> 300 Permanent sterility in women
500 Fatal (often within 2 months) destruction of bone marrow and
intestine
1000 Fatal (often within 2 weeks)
2000 Fatal (often within hours)
http://2012books.lardbucket.org/books/principles-of-general-chemistry-v1.0/s24-nuclear-chemistry.html
Symptoms of Exposure
5/29/2018
5
� The rate of decay, as well as the type and energy
of the radiation, determines the damage caused by
radiation.
� Nuclear decay follows first-order kinetics, which
gives a constant t1/2 over the course of the decay.
� Typically we are given half-life (t1/2) values. We
can use these to calculate rate constants (or decay
constants) for radioactive nuclides.
Nuclear Decay – Half-Lives
25 26
All radioactive decays obey first-order kinetics.
No = amount at beginning (if %, No = 100%)
Nt = amount (mass or %) remaining after time
k = rate or decay constant, with units (1st order: time-1)
t = time
Half-life is the time it takes for the amount of a substance to
decrease by 50%.
Nuclear Radioactivity
First Order Decay
CC-BY-NA-3.0: http://chemwiki.ucdavis.edu/Wikitexts/Heartland_Community_College/HCC%3A_Chem_162/21%3A_Nuclear_Chemistry/21.1%3A_Radioactivity
� Can use kinetics equations, just like in Chapter 12, to perform calculations:
� How much nuclide (mass or %) is left after ___ time?
� How long does it take for ___% to decay (or remain)?
� The half-life for sodium-24, a radioisotope used
medically in blood studies, is 906 minutes. What is
the rate constant for 24Na (in hr-1)?
� 4.59 x 10-2 hr -1
28
Nuclear Decay - Kinetics
� If you ingest a 75.0 mg sample of 131I with a rate
constant of 0.0861 d-1, how long would it take to decay
to 12.5 mg?� t = 20.8 days
� Gold-128 undergoes beta decay to give mercury-128
with a half-life of 2.7 days. If you start with 5.6 mg of 128Au, what mass of gold-128 is left after 9.5 days?� Nt = 0.49 mg
� 214Bi decays by alpha emission with a half-life of 19.7 min. How long does it take for 75.0% of 214Bi to decay?� k = 0.035178 min-1; t = 39.4 min
� Examples 21.5 – 21.729
Group Work
30
Video about fallout from Chernobyl(46 min.):
http://www.youtube.com/watch?v=GezeZlu70oI
10 Interesting Facts about Chernobyl:
http://imgur.com/gallery/AfbNLQ9
Fermi and the “Atomic Pile”: http://www.fi.edu/learn/case-
files/fermi/pile.html
Distribution and history of energy sources: http://www.world-
nuclear.org/info/Current-and-Future-Generation/Nuclear-Power-in-
the-World-Today/#.Uebm_ZyETLc
How geological dating on rocks is done:
http://www.youtube.com/watch?v=1920gi3swe4
Informative/Interesting Links
5/29/2018
6
http://www.world-nuclear.org/info/inf01.html
http://www.nucleartourist.com/basics/why.htm� List of advantages/disadvantages
of each energy source.
Global Energy Sources World Energy Consumption
https://en.wikipedia.org/wiki/Renewable_energy#/media/File:Total_World_Energy_Consumption_by_Source_2013.png
� Energy released from 200 g U = 2x1013 J
� Energy released from 1 ton coal = 5x107 J
� It would take 1 million tons of coal to create the
same amount of energy.
� Nuclear power plants don’t explode (like TNT)
unless an uncontrolled nuclear chain reaction occurs.
When nuclear power plants have meltdowns, the
threat is from leakage of radioactive material (water,
airborne, soil contamination, etc.)
Nuclear Energy
33 34
Schematic of a cyclotron particle accelerator.
21.4 Nuclear Transmutation
http://www.physbot.co.uk/magnetic-fields-and-induction.html
35
Nuclear transmutation differs from radioactive decay in
that transmutation is brought about by the collision of two
particles.
Particle accelerators made it possible to synthesize the so-
called transuranium elements, elements with atomic
numbers greater than 92.
Transmutation
+ +
36
A Linear Particle Accelerator. (a) An aerial view of the SLAC, the longest linear
particle accelerator in the world; the overall length of the tunnel is 2 miles. (b)
Rapidly reversing the polarity of the electrodes in the tube causes the charged
particles to be alternately attracted as they enter one section of the tube and repelled
as they leave that section. As a result, the particles are continuously accelerated
along the length of the tube.
Transmutation
CC-BY-NA-3.0: http://chemwiki.ucdavis.edu/Wikitexts/Heartland_Community_College/HCC%3A_Chem_162/21%3A_Nuclear_Chemistry/21.1%3A_Radioactivity
5/29/2018
7
37
Nuclear fission: heavy nuclei (mass number > 200) are
bombarded by neutrons to form smaller nuclei and one or more
neutrons. Used in nuclear power plants.
Nuclear Fission
CC-BY-NA-3.0: http://chemwiki.ucdavis.edu/Wikitexts/Heartland_Community_College/HCC%3A_Chem_162/21%3A_Nuclear_Chemistry/21.1%3A_Radioactivity
38
235U is capable of a self-sustaining sequence of nuclear fission
known as a nuclear chain reaction. The minimum mass of
material required to generate a self-sustaining chain reaction is the
critical mass.
Nuclear Fission
CC-BY-NA-3.0: http://chemwiki.ucdavis.edu/Wikitexts/Prince_Georges_Community_College/General_Chemistry_for_Engineering/Unit_7%3A_Nuclear_Chemistry/Chapter_18%3A_Nuclear_Chemistry/Chapter_18.1%3A_The_Components_of_the_Nucleus
39
Nuclear Fissionyoutube video
CC-BY-NA-3.0: http://chemwiki.ucdavis.edu/Wikitexts/Heartland_Community_College/HCC%3A_Chem_162/21%3A_Nuclear_Chemistry/21.1%3A_Radioactivity
(a)The Diablo Canyon Nuclear Power Plant near San Luis Obispo is the only nuclear power
plant currently in operation in California. The domes are the containment structures for the
nuclear reactors, and the brown building houses the turbine where electricity is generated.
Ocean water is used for cooling. (b) The Diablo Canyon uses a pressurized water reactor, one
of a few different fission reactor designs in use around the world, to produce electricity.
Energy from the nuclear fission reactions in the core heats water in a closed, pressurized
system. Heat from this system produces steam that drives a turbine, which in turn produces
electricity. (credit a: modification of work by “Mike” Michael L. Baird; credit b: modification
of work by the Nuclear Regulatory Commission)
� The decay of radioactive isotopes allows for the relative age of once-living things to be calculated.
� Radiocarbon dating uses 14C
� Living things have a dynamic equilibrium of 14C in their system (ex: inhaling/exhaling)
� When a plant or animal dies, it no longer incorporates new 14C, and the 14C begins to decay, causing the 14C content to become less than that in the atmosphere.
� 146C � 14
7N + 0-1e-
C -14 Dating: http://www.youtube.com/watch?v=81dWTeregEA&feature=related
40
21.5 Archeological Dating
� Geological dating is similar to archeological dating, but uses longer-lived nuclides
� Measure ratio of 40K to 40Ar in rocks
� 4019K + 0-1e � 40
18Ar
� 4019K � 40
20Ca + 0-1e
� 40K has a half-life of 1.28x109 years
� Rocks are crushed, 40Ar escapes, and the ratio of 40K to 40Ar is measured.
� This allowed the age of the earth to be calculated to be 4.5 billion years.
Radiometric Dating: http://www.youtube.com/watch?v=1920gi3swe4
41
Geological Dating
� Three-Mile Island (Pennsylvania, 1979): Caused by
mechanical failures; small radiation leak (not linked to a
cancer fatality, no observable long term health effects).
� Chernobyl (Ukraine, 1986): No containment, 31 deaths
attributed to accident, radiation leak caused health issues
(50,000 excess cancer cases).
� Fukushima, Japan (March 2011): Not caused by
earthquake – low-lying generators flooded from tsunami;
seawater to cool down reactors used too late. Single-
replacement reaction produced hydrogen gas causing
several chemical explosions. Radioactivity release about
1/10 of Chernobyl.
Well-Known Incidents
42
5/29/2018
8
43
Nuclear fusion is the process of combining small nuclei
into larger ones (up to 59Fe). Because fusion reactions take
place at very high temperatures, they are often called
thermonuclear reactions.
Nuclear Fusion
CC-BY-NA-3.0: http://chemwiki.ucdavis.edu/Wikitexts/Prince_Georges_Community_College/General_Chemistry_for_Engineering/Unit_7%3A_Nuclear_Chemistry/Chapter_18%3A_Nuclear_Chemistry/Chapter_18.1%3A_The_Components_of_the_Nucleus
44
ITER: France – building the Tokamak, a device that uses
magnetic fields to contain and control hot plasma needed
for fusion.
Due to the high temperature
requirements, containment
is an issue.
Nuclear Fusion
https://en.wikipedia.org/wiki/Tokamak_Fusion_Test_Reactor
45
Radioactive and stable isotopes have
applications in science and medicine.
Radioactive isotopes are used as
tracers.
Use of tracers for diagnosis include:
�Sodium-24 – blood flow
� Iodine-131 – thyroid conditions
� Iodine-123 – brain imaging
21.5 Uses of Isotopes
45https://en.wikipedia.org/wiki/Brain_positron_emission_tomography
46
The fundamental unit of radioactivity is the curie (Ci)
1 Ci = 3.70 x 1010 disintegrations per second.
21.6 Biological Effects of Radiation
https://en.wikipedia.org/wiki/Geiger_counter
47
A common unit for the absorbed dose of radiation is the
rad (radiation absorbed dose).
1 rad = 1 x 10−5 J/g of tissue irradiated
The rem (roentgen equivalent for man) is determined from
the number of rads:
Number of rems = number of rads x 1 RBE
RBE = the relative biological effectivness.
Biological Effects of Radiation