1 nuclear chemistry 2 radioactivity one of the pieces of evidence for the fact that atoms are made...
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RadioactivityRadioactivity
• One of the pieces of evidence for the One of the pieces of evidence for the fact that atoms are made of smaller fact that atoms are made of smaller particles came from the work ofparticles came from the work of
________ ________ (1876-1934).(1876-1934). • She discoveredShe discovered ________________, the , the
spontaneous disintegration of some spontaneous disintegration of some elements into smaller pieces.elements into smaller pieces.
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Some nuclei are unstable
Unstable nuclei will naturally release particles and/or energy to become more
stable
7Nuclear Reactions vs. Nuclear Reactions vs. Normal Chemical Normal Chemical
ChangesChanges• Nuclear reactions involve the nucleusNuclear reactions involve the nucleus• The nucleus opens, and protons and The nucleus opens, and protons and
neutrons are rearrangedneutrons are rearranged• The opening of the nucleus releases a The opening of the nucleus releases a
tremendous amount of energy that holds tremendous amount of energy that holds the nucleus together – called the nucleus together – called binding binding energyenergy
• ““Normal” Chemical Reactions involve Normal” Chemical Reactions involve electronselectrons, not protons and neutrons, not protons and neutrons
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Mass DefectMass Defect
• Some of the mass can be converted into Some of the mass can be converted into energyenergy
• Shown by a very famous equation!Shown by a very famous equation!
E=mcE=mc22
EnergyEnergy
MassMass
Speed of lightSpeed of light
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Types of RadiationTypes of Radiation
e01
He42
• Alpha (Alpha (άά) – a positively ) – a positively charged helium isotopecharged helium isotope - - we we usually ignore the charge because it involves usually ignore the charge because it involves electrons, not protons and neutronselectrons, not protons and neutrons
•Beta (Beta (ββ) – an electron) – an electron
•Gamma (Gamma (γγ) – pure energy; ) – pure energy; called a ray rather than a called a ray rather than a particleparticle
00
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Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General ChemistryGeneral Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline., 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline.
Alpha particles (α)• They are known to consist of They are known to consist of helium-4 nucleihelium-4 nuclei (nuclei (nuclei
with two protons and two neutrons)with two protons and two neutrons)
• Positive chargePositive charge
• Slow moving Slow moving
• Stopped by small barriers as thin as few pages of Stopped by small barriers as thin as few pages of paperpaper
• Symbolized in the following ways:Symbolized in the following ways:
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Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General ChemistryGeneral Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline., 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline.
Beta particles ()They are known to consist of They are known to consist of high speed electrons high speed electrons emitted from the nucleusemitted from the nucleus
Negative chargeNegative charge
Higher speed particles therefore, more penetrating than Higher speed particles therefore, more penetrating than alpha particlesalpha particles
stopped by only more dense materials such as wood, stopped by only more dense materials such as wood, metal, or several layers of clothingmetal, or several layers of clothing
The symbol is basically equivalent to an electronThe symbol is basically equivalent to an electron
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Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General ChemistryGeneral Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline., 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline.
Gamma rays ()• They have been shown to be a form of They have been shown to be a form of
electromagnetic radiation (pure energy)electromagnetic radiation (pure energy)
• is pure energy (no p, n, e)is pure energy (no p, n, e)
• Highly energetic, the most penetrating form of Highly energetic, the most penetrating form of radiation radiation
• barriers of lead, concrete, or more often, a barriers of lead, concrete, or more often, a combination is required for protection.combination is required for protection.
• Symbol is Symbol is
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Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. Material was developed by combining Janusa’s material with the lecture outline provided with Ebbing, D. D.; Gammon, S. D. General ChemistryGeneral Chemistry, 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline., 8th ed., Houghton Mifflin, New York, NY, 2005. Majority of figures/tables are from the Ebbing lecture outline.
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Other Nuclear ParticlesOther Nuclear Particles
e01
n10• NeutronNeutron
• Positron – a positive Positron – a positive electronelectron
•Proton – usually referred to Proton – usually referred to as hydrogen-1as hydrogen-1
•Any other elemental isotopeAny other elemental isotope
H11
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Balancing Nuclear ReactionsBalancing Nuclear Reactions•In the reactants (starting materials – on the left side of an equation) and products (final products – on the right side of an equation)
Atomic numbers must balanceand
Mass numbers must balance
•Use a particle or isotope to fill in the missing protons and neutrons
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Nuclear ReactionsNuclear Reactions• Alpha emissionAlpha emission
Note that mass number (A) goes down by 4 and atomic number (Z) goes down by 2.
Nucleons (nuclear particles… protons and neutrons) are rearranged but conserved
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Nuclear ReactionsNuclear Reactions• Beta emissionBeta emission
Note that mass number (A) is unchanged and atomic number (Z) goes up by 1.
23Other Types of Nuclear Other Types of Nuclear ReactionsReactions
Positron (Positron (00+1+1): a positive electron): a positive electron
Electron capture: Electron capture: the capture of an electron
207 207
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Learning Check
What radioactive isotope is produced in the following bombardment of boron?
10B + 4He ? + 1n
5 2 0
26Artificial Nuclear Artificial Nuclear ReactionsReactions
New elements or new isotopes of known elements New elements or new isotopes of known elements are produced by bombarding an atom with a are produced by bombarding an atom with a subatomic particle such as a proton or neutron -- subatomic particle such as a proton or neutron -- or even a much heavier particle such as or even a much heavier particle such as 44He and He and 1111B.B.
Reactions using neutrons are called Reactions using neutrons are called
reactions reactions because a because a ray is usually ray is usually emitted.emitted.
Radioisotopes used in medicine are often made by Radioisotopes used in medicine are often made by reactions. reactions.
27Artificial Nuclear Artificial Nuclear ReactionsReactions
Example of a Example of a reaction reaction is production is production
of radioactive of radioactive 3131P for use in studies of P P for use in studies of P
uptake in the body.uptake in the body.
31311515P + P + 11
00n ---> n ---> 32321515P + P +
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Transuranium ElementsTransuranium Elements
Elements beyond 92 Elements beyond 92 (transuranium)(transuranium) made made
starting with an starting with an reaction reaction
2382389292U + U + 11
00n ---> n ---> 2392399292U + U +
2392399292U U ---> ---> 239239
9393Np + Np + 00-1-1
2392399393Np Np ---> ---> 239239
9494Pu + Pu + 00-1-1
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Nuclear FissionNuclear FissionFission is the splitting of atomsFission is the splitting of atoms
These are usually very large, so that they are not as stableThese are usually very large, so that they are not as stable
Fission chain has three general steps:Fission chain has three general steps:
1.1. Initiation.Initiation. Reaction of a single atom starts the Reaction of a single atom starts the
chain (e.g., chain (e.g., 235235U + neutron)U + neutron)
2.2. PropagationPropagation. . 236236U fission releases neutrons that U fission releases neutrons that
initiate other fissionsinitiate other fissions
3. 3. ___________ ___________ . .
31Stability Stability of of NucleiNuclei
• Out of > 300 stable isotopes:
EvenEven OddOdd
OddOdd
EvenEven
ZZNN
157157 5252
5050 55
31311515PP
191999FF
2211H, H, 66
33Li, Li, 101055B, B, 1414
77N, N, 1801807373TaTa
34Nuclear Fission & Nuclear Fission & POWERPOWER
• Currently about 103 Currently about 103
nuclear power plants in nuclear power plants in
the U.S. and about 435 the U.S. and about 435
worldwide.worldwide.
• 17% of the world’s 17% of the world’s
energy comes from energy comes from
nuclear.nuclear.
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Nuclear Fusion
Fusion small nuclei combine
2H + 3H 4He + 1n +
1 1 2 0
Occurs in the sun and other stars
Energy
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Nuclear Fusion
Fusion
• Excessive heat can not be contained
• Attempts at “cold” fusion have FAILED.
• “Hot” fusion is difficult to contain
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Half-LifeHalf-Life
•HALF-LIFEHALF-LIFE is the time that it takes for is the time that it takes for 1/2 a sample to decompose.1/2 a sample to decompose.
• The rate of a nuclear transformation The rate of a nuclear transformation depends only on the “reactant” depends only on the “reactant” concentration.concentration.
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Half-LifeHalf-Life
Decay of 20.0 mg of Decay of 20.0 mg of 1515O. What remains after 3 half-lives? O. What remains after 3 half-lives? After 5 half-lives?After 5 half-lives?
40Kinetics of Radioactive Kinetics of Radioactive DecayDecay
For each duration (half-life), one half of the substance
decomposes.
For example: Ra-234 has a half-life of 3.6 days
If you start with 50 grams of Ra-234
After 3.6 days > 25 gramsAfter 3.6 days > 25 grams
After 7.2 days > 12.5 gramsAfter 7.2 days > 12.5 grams
After 10.8 days > 6.25 gramsAfter 10.8 days > 6.25 grams
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Learning Check!
The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 39 hours?
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Radiocarbon DatingRadiocarbon DatingRadioactive C-14 is formed in the upper atmosphere Radioactive C-14 is formed in the upper atmosphere
by nuclear reactions initiated by neutrons in cosmic by nuclear reactions initiated by neutrons in cosmic radiationradiation
1414N + N + 11oon ---> n ---> 1414C + C + 11HH
The C-14 is oxidized to COThe C-14 is oxidized to CO22, which circulates through , which circulates through
the biosphere.the biosphere.
When a plant dies, the C-14 is not replenished.When a plant dies, the C-14 is not replenished.
But the C-14 continues to decay with tBut the C-14 continues to decay with t1/21/2 = 5730 years. = 5730 years.
Activity of a sample can be used to date the sample.Activity of a sample can be used to date the sample.
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Technetium-99Technetium-99
Brain tumor detection and treatmentsBrain tumor detection and treatments
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Plutonium (Pu)Plutonium (Pu)
Uranium (U)Uranium (U)
Nuclear FuelsNuclear Fuels
For power plants or nuclear weaponsFor power plants or nuclear weapons
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• Decreased white blood cell count
• Lesions
• Nausea and diarrhea
• Birth defects
• Hair loss
• Bleeding
• Death
HEALTH EFFECTS OF RADIATION EXPOSURE
55This is the hand of a physician who was This is the hand of a physician who was
exposed to repeated small doses of x-ray exposed to repeated small doses of x-ray radiation for 15 years. The skin cancer radiation for 15 years. The skin cancer
appeared several years after his work with appeared several years after his work with x-rays had ceased. Cancer incidence x-rays had ceased. Cancer incidence
depends on radiation dose. depends on radiation dose. From Meissner, William A. and Warren, From Meissner, William A. and Warren,
Shields: Neoplasms, In Anderson W.A.D. editor; Pathology, edition 6, St. Louis, 1971, The C.V. Mosby CoShields: Neoplasms, In Anderson W.A.D. editor; Pathology, edition 6, St. Louis, 1971, The C.V. Mosby Co