Date post: | 17-Jan-2018 |
Category: |
Documents |
Upload: | barrie-oliver |
View: | 226 times |
Download: | 0 times |
If you can't read please download the document
Unit 12- Nuclear Chemistry
Nucleon Positron Radioactive Radioisotope Tracer Transmutation
Alpha particle Artificial transmutation Beta particle Fission
Fusion Gamma ray Half-life Natural transmutation Nuclear Reactions
Involve the nucleus of an atom
nucleons- protons and neutrons The nucleus opens, and protons and
neutrons are rearranged This releases a tremendous amount of energy
that holds the nucleus together called binding energy
Transmutation- when an atomic nucleus changes into the nucleus of
another element Normal Chemical Reactions involve electrons, not
protons and neutrons Strong force- what holds the nucleus together
acts on particles that are close together Nuclear stability Ratio
of neutrons to protons
Belt is located above a 1:1 ratio of neutrons to protons but below
a 2:1 ratio Nuclei with atomic numbers above 83 are unstable
Therefore they are radioactive Too many neutrons, high
neutron:proton ratio What is a radioactive atom? An unstable
nucleus that spontaneously decays to form a more stable product
Called a radioisotope When a nucleus decays it will emit radiation
in these possible forms:
Alpha particle- Helium nucleus Beta particle- Has a 1- charge
Positron- has a 1+ charge Similar to beta particle but opposite
charge Gamma rays- Almost all nuclear decay emits some; similar to
X-rays but has greater E~ high energy photons Table O!! Penetrating
ability of radiation
Gamma Deflection of Particles
Negative Positive Alpha Emission (decay)
226 4 222 Ra He + Rn 88 2 86 Alpha Particle Radium-226 Radon-222
__________________________________________ Mass Number (P+N) 226 =
4 + 222 = Atomic Number(protons only) 88 2 + 86 Nuclide= a
particular type of nucleus, characterized by a specific atomic
number and nucleon number Nucleons (protons and neutrons) are
rearranged but conserved The Law of Conservation of Matter is
obeyed Atomic # decreases by 2, atomic mass decreases by 4 Table N
Alpha Emission Example: Beta Emission (decay) U e + Np
239 239 U e + Np 92 -1 93 Beta Particle Uranium-239 Neptunium-239
__________________________________________ Mass Number (P+N) 239 =
+ 239 = Atomic Number(protons only) 92 -1 + 93 Law of Conservation
is followed Atomic number goes up by one Atomic mass remains
unchanged Beta Emission Example: Positron Emission (decay)
207 207 Po e + Bi 84 +1 83 Positron Bismuth-207 Polonium-207
__________________________________________ Mass Number (P+N) 207 =
+ 207 = + Atomic Number(protons only) 84 +1 83 Law of Conservation
is followed Atomic number goes down by one Atomic mass remains
unchanged Positron Emission Example:
Same result when a nucleus captures its least energetic electron
K-capture Gamma Emission The nucleus has energy levels just like
electrons, but they involve a lot more energy. When the nucleus
becomes more stable, a gamma ray may be released. This is a photon
of high-energy light, and has no mass or charge. The atomic mass
and number do not change with gamma. Gamma may occur by itself, or
in conjunction with any other decay type Gamma Emission Example:
Rules for Writing Nuclear Equations
The mass on each side of the equation must be equal The charges on
each side of the equation must be equal General Format XX+ Y A Z a
z A-a Z-z Types of transmutations
Natural- The decay methods already discussed Alpha, beta, positron,
gamma Natural; due to unstable nuclei Has 1 reactant Artificial- (2
types) 1- collide charged particle with target nucleus Accelerate
protons or alpha particles to overcome repulsive forces from
nucleus 1- the particles have to have enough E to overcome the
repulsive forces between positively charged particle and positively
charged nucleus this E is supplied by accelerating particles by
magnetic or electrostatic fields, these machines are called
synchotrons Most of the elements from 93 on up (the transuranium
elements) were created using particle accelerators. 2- collide
neutron with target nucleus
Neutrons are obtained as nuclear reaction by-products; they are
captured by nucleuss strong force Used to prepare radioisotopes
from stable nuclei Has 2 reactants 2- the reactions that donate the
neutrons are similar to the reactions that create
electricity.Neutron has no charge so it isnt repelled from the
nucleus, its captured by the forces that hold the protons and
neutrons in nucleus Cyclotron linear accelerator Nuclear Fission A
heavy nucleus is split into two smaller nuclei with release of
energy Mass is converted to energy (E = mc2) 1 235 92 141 n 1 + U
Kr + Ba + 3 n 92 36 56 Fission- 2 ss so it splits 1 into 2 Fusion 1
smakes 1 fuses Because neutrons are reactants and products, a chain
reaction occurs
Fission Neutron causes a large nucleus to split into smaller ones.
Used in nuclear reactors. 10n + 23592U + 9136Kr + 3(10n) 14256Ba
Because neutrons are reactants and products, a chain reactionoccurs
Nuclear Fission Nuclear Fusion Two lighter nuclei are fused to form
a heavier nucleus
1 4 H He + 2 4 e + energy (E = mc2) 1 2 -1 2 4 2 H He + energy (E =
mc2) 1 2 20% of our electricity for our country is nuclear Waste is
stored in spent fuel pools advantage:products arent highly
radioactive like fission The process that occurs in stars and
thermonuclear weapons (hydrogen bombs) Fusion Combining of light
nuclei to form heavier ones. Lots of energy required to start it,
but lots of energy released. In Sun: The equations on this slide
happen on the sun are still unable to do on Earth due to the
tremendous temperature and pressure needed tor the reaction to take
place 4(11H) 2(0+1e) 42He + Energy in Nuclear Reactions
Nuclear reactions result in a loss of a small amount of mass and,
therefore, release a large amount of energy. E = mc2 Over 1 billion
times more energy is produced in a nuclear reaction than in any
other type of reaction The matter thats converted into the energy
is called the MASS DEFECT Radioactive decay substances decay at a
constant rate, regardless of temperature, pressure, etc Random
event that cant be predicted Table N shows mode of decay for some
radioactive elements More to Table N than this! Half-life The time
it takes for half the atoms in a given sample of an element to
decay Each radioisotope has its own half-life Shorter half-life =
more unstable Half-life equations Table T in reference tables n=
t/T
n = number of half-lives t= time elapsed T= half-life Fraction of
remaining: (1/2)n or (1/2)t/T Original mass= final mass x 2n Decay
of 20. 0 mg of Oxygen-15. What remains after 3 half-lives
Decay of 20.0 mg of Oxygen-15. What remains after 3 half-lives?
After 5 half-lives? Has a half life of 122 seconds 20 mg 10 mg 5 mg
2.5 mg Going Forwards in Time How many grams of a 10.0 gram sample
of I-131 (half-life of 8 days) will remain in 24 days? #HL = t/T =
24/8 = 3 Cut 10.0g in half 3 times:5.00, 2.50, 1.25g Going
Backwards in Time
How many grams of a 10.0 gram sample of I-131 (half-life of 8 days)
would there have been 24 days ago? #HL = t/T = 24/8 = 3 Double
10.0g 3 times:20.0, 40.0, 80.0 g Radioactive Dating A sample of an
ancient scroll contains 50% of the original steady-state
concentration of C-14.How old is the scroll? 50% = 1 HL 1 HL X 5730
y/HL = 5730y Uses of Radioisotopes Radioactive dating
Carbon-14 for dating organic remains Potassium-40 for dating rocks
Uranium-238 for determining the age of the earth Radiation therapy
for cancer
Destroy cancer cells (can damage healthy cells) Irradiation of food
Cobalt-60 produces gamma rays- kill bacteria Tracers Carbon-14 for
photosynthesis Iodine-131 for thyroid disorders Technetium-99 for
diagnosis of brain tumors Carbon-13 for real-time brain imaging
(PET Scan) Why do these uses require short half-lives? Short
half-lives so they dont stay in body long Other Uses of Radioactive
Isotopes
C-14: Carbon Dating (Finding Age of Organic Material) U-238:
Geological Dating (Finding Age of Inorganic Material) U-235:
Nuclear Power Plant Fuel P-31: Tracer in Plant Fertilizer I-131:
Detection and Treatment of Thyroid Conditions Tc-99: Cancer
Detection and Location Co-60: Cancer Treatment and destruction of
bacteria Cs-137: Destruction of Bacteria