Nuclear Chemistry
description
Transcript of Nuclear Chemistry
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NUCLEAR CHEMISTRYUnit 2.5
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Introduction to Nuclear Chemistry
Nuclear chemistry is the study of the structure of and the they undergo.
atomic nuclei changes
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Chemical vs. Nuclear ReactionsChemical Reactions Nuclear Reactions
Bonds are broken
Nuclei emit particles and/or rays
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Chemical vs. Nuclear ReactionsChemical Reactions Nuclear ReactionsBonds are broken Nuclei emit particles and/or rays
Atoms are rearranged
Atoms changed into atoms of another element
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Chemical vs. Nuclear ReactionsChemical Reactions Nuclear ReactionsBonds are broken Nuclei emit particles and/or raysAtoms may be rearranged Atoms changed to atoms of
different element
Involve valence electrons
Involve protons, neutrons, and/or electrons
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Chemical vs. Nuclear ReactionsChemical Reactions Nuclear ReactionsBonds are broken Nuclei emit particles and/or raysAtoms are rearranged Atoms change into atoms of
different elementInvolve valence electrons Involve protons, neutrons, and/or
electrons
Small energy changes
Large energy changes
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Chemical vs. Nuclear ReactionsChemical Reactions Nuclear ReactionsBonds are broken Nuclei emit particles and/or raysAtoms are rearranged Atoms change into atoms of
different elementInvolve valence electrons Involve protons, neutrons, and/or
electronsSmall energy changes Large energy changes
Reaction rate can be changed.
Reaction rate cannot be changed
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The Discovery of Radioactivity (1895 – 1898):
found that invisible rays were emitted when electrons hit the surface of a fluorosent screen (discovered x-rays)
Becquerel accidently discovered that phosphorescent rock produced spots on photographic plates
Roentgen
uranium
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The Discovery of Radioactivity (1895 – 1898):
isolated the components (
atoms) emitting the rays – process by
which atoms give off – the penetrating
rays and particles by a radioactive source
Marie and Pierre Curieuranium
Radioactivityrays or particlesRadiationemitted
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The Discovery of Radioactivity (1895 – 1898):
identified 2 new elements, and on the basis of their radioactivity
These findings Dalton’s theory of indivisible atoms.
poloniumradiumcontradi
cted
Marie Curie, continued
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The Discovery of Radioactivity (1895 – 1898):
– atoms of the same element with different numbers of – isotopes of atoms with unstable nuclei
(too many or too few neutrons) – when
unstable nuclei lose energy by emitting to become more
IsotopesneutronsRadioisotopes
Radioactive decayradiationstableSpontaneous Reaction!
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Alpha radiation Composition – Alpha particles, same as
helium nuclei Symbol – Helium nuclei, He, α Charge – 2+ Mass (amu) – 4 Approximate energy – 5 MeV Penetrating power – low (0.05 mm body
tissue) Shielding – paper, clothing
42
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Beta radiation Composition – Beta particles, same as an
electron Symbol – e-, 0
-1β Charge – 1- Mass (amu) – 1/1837 (practically 0) Approximate energy – 0.05 – 1 MeV Penetrating power – moderate (4 mm body
tissue) Shielding – metal foil
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Gamma radiation Composition – High-energy
electromagnetic radiation Symbol – o
oγ Charge – 0 Mass (amu) – 0 Approximate energy – 1 MeV Penetrating power – high (penetrates body
easily) Shielding – lead, concrete
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Review of Atomic StructureNucleus Electron Cloud
99.9% of the mass1/10,000 the size of the atom
0.01% of the mass 9,999 times the size of the nucleus
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Review of Atomic StructureNucleus Electron Cloud99.9% of the mass1/10,000 the size of the atom
0.01% of the mass, 9,999 times the size of the nucleus
Protons (p+) and neutrons (n0)
Electrons (e-)
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Review of Atomic StructureNucleus Electrons99.9% of the mass1/10,000 the size of the atom
0.01% of the mass, 9,999 times the size of the nucleus
Protons (p+) and neutrons (n0) Electrons (e-)
Positively charged
Negatively charged
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Review of Atomic StructureNucleus Electrons99.9% of the mass1/10,000 the size of the atom
0.01% of the mass, 9,999 times the size of the nucleus
Protons (p+) and neutrons (n0) Electrons (e-)Positively charged Negatively charged
Strong nuclear force (holds the protons together)
Weak electrostatic force (between electrons and nucleus
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Chemical SymbolsA chemical symbol looks like…
p+ = e- = atomic #
To find the number of , subtract the
from the
C614
mass #atomic #
mass #atomic #neutrons
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Nuclear Stability Isotope is completely stable if the
nucleus will spontaneously .
Elements with atomic #s to are . ratio of protons:neutrons (
) Example: Carbon – 12 has protons
and neutrons
notdecompose201very stable1:1 p+:n0
6 6
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Nuclear Stability Elements with atomic #s to are
.
ratio of protons:neutrons (p+ : n0) Example: Mercury – 200 has
protons and neutrons
2183marginally stable1:1.5 12080
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Nuclear Stability Elements with atomic #s are and . Examples: and
> 83radioactive unstablePlutoniumUranium
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Alpha Decay Alpha decay – emission of an alpha
particle ( ), denoted by the symbol , because an α has 2 protons and 2 neutrons, just like the He nucleus. Charge is because of the 2 .
Alpha decay causes the number to decrease by and the number to decrease by .
determines the element. All nuclear equations are .
α42He
4mass
+2 protonsatomic
Atomic number balanced2
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Alpha Decay Example 1: Write the nuclear equation
for the radioactive decay of polonium – 210 by alpha emission.
Step 1: Write the element that you are starting with.210Po84
Mass #
Atomic #
Step 2: Draw the arrow.Step 3: Write the alpha particle.Step 4: Determine the other product (ensuring everything is balanced).
4He2 206Pb82
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Alpha Decay Example 2: Write the nuclear equation
for the radioactive decay of radium – 226 by alpha emission.
Step 1: Write the element that you are starting with.226Ra88
Mass #
Atomic #
Step 2: Draw the arrow.Step 3: Write the alpha particle.Step 4: Determine the other product (ensuring everything is balanced).
4He2 222Rn86
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Beta decay Beta decay – emission of a beta particle (
), a fast moving , denoted by the symbol or . β has insignificant mass ( ) and the charge is because it’s an .
Beta decay causes change in number and causes the number to increase by .
A neutron is converted to a proton and a beta particle.
β0electron-1
no mass1atomic
electron e-e0-1
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Beta Decay Example 1: Write the nuclear equation
for the radioactive decay of carbon – 14 by beta emission.
Step 1: Write the element that you are starting with.14 C6
Mass #
Atomic #
Step 2: Draw the arrow.Step 3: Write the beta particle.Step 4: Determine the other product (ensuring everything is balanced).
0e-1 14N7
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Beta Decay Example 2: Write the nuclear equation
for the radioactive decay of zirconium – 97 by beta decay.
Step 1: Write the element that you are starting with.97Zr40
Mass #
Atomic #
Step 2: Draw the arrow.Step 3: Write the beta particle.Step 4: Determine the other product (ensuring everything is balanced).
0e-1 97Nb41
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Gamma decay Gamma rays – high-energy
radiation, denoted by the symbol . γ has no mass ( ) and no charge ( ).
Thus, it causes change in or numbers. Gamma rays almost
accompany alpha and beta radiation. However, since there is effect on mass number or atomic number, they are usually from nuclear equations.
electromagneticγ0 0no mass atomic
alwaysno
omitted
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Transmutation
the of an atom of one element to an atom of a different element.
Radioactive decay is one way that this occurs!
Transmutationconversion
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ReviewType of
Radioactive
Decay
Particle
Emitted
Change in Mass
#
Change in
Atomic #
Alpha α He
-4 -2
Beta β e 0 +1Gamma γ 0 0
420
-1
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Half-Life is the required
for of a radioisotope’s nuclei to decay into its products.
For any radioisotope,# of ½ lives % Remaining0 100%1 50%2 25%3 12.5%4 6.25%5 3.125%6 1.5625%
Half-life time half
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Half-Life
0 1 2 3 4 5 6 70
10
20
30
40
50
60
70
80
90
100
Half-Life
# of Half-Lives
% R
emai
ning
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Half-Life For example, suppose you have 10.0
grams of strontium – 90, which has a half life of 29 years. How much will be remaining after x number of years?
You can use a table:# of ½ lives
Time (Years)
Amount Remaining (g)
0 0 101 29 52 58 2.53 87 1.254 116 0.625
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Half-Life Or an equation!
mt = m0 x (0.5)n
mass remaining
initial mass
# of half-lives
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Half-Life Example 1: If gallium – 68 has a half-life
of 68.3 minutes, how much of a 160.0 mg sample is left after 1 half life? ________ 2 half lives? __________ 3 half lives? __________
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Half-Life Example 2: Cobalt – 60, with a half-life of
5 years, is used in cancer radiation treatments. If a hospital purchases a supply of 30.0 g, how much would be left after 15 years? ______________
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Half-Life Example 3: Iron-59 is used in medicine
to diagnose blood circulation disorders. The half-life of iron-59 is 44.5 days. How much of a 2.000 mg sample will remain after 133.5 days? ______________
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Half-Life Example 4: The half-life of polonium-218
is 3.0 minutes. If you start with 20.0 g, how long will it take before only 1.25 g remains? ______________
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Half-Life Example 5: A sample initially contains
150.0 mg of radon-222. After 11.4 days, the sample contains 18.75 mg of radon-222. Calculate the half-life.
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Nuclear Reactions Characteristics: Isotopes of one element are
into isotopes of another element Contents of the change amounts of are
released
changednucleusLarge energy
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Types of Nuclear Reactions
decay – alpha and beta particles and gamma ray emission
Nuclear - emission of a or
Radioactivedisintegrationneutronproton
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Nuclear Fission - of a nucleus - Very heavy nucleus is split into
approximately fragments - reaction releases several neutrons
which more nuclei - If controlled, energy is released
(like in ) Reaction control depends on reducing the of the neutrons (increases the reaction rate) and extra neutrons ( creases the reaction rate).
Fissionsplitting
slowlysplitChainequal two
nuclear reactorsspeeddeabsorbing
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Nuclear Fission - 1st controlled nuclear reaction in
December 1942. 1st uncontrolled nuclear explosion occurred July 1945.
- Examples – atomic bomb, current nuclear power plants
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Nuclear Fission Disadvantages
Produces high level radioactive waste that must be stored for 10,000’s of years.
Meltdown causes disasters like in Japan and Chernobyl.
Advantages Zero air pollution Not a fossil fuel so doesn’t contribute to
climate change
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Nuclear Fusion - Fusion: Combining of two nuclei - Two light nuclei combine to form a single
heavier nucleus - Does not occur under standard conditions
(positive nuclei repel each other) - Advantages compared to fission – No
radioactive waste, inexpensive ,
- Disadvantages - requires large amount of energy to start, difficult to control.
- Examples – energy output of stars, hydrogen bomb, future nuclear power plants
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Uses of Radiation Radioactive dating: Carbon–14 used to
determine the age of an object that was once alive.
Detection of diseases: Iodine–131 used to detect thyroid problems, technetium–99 used to detect cancerous tumors and brain disorders, phosphorus – 32 used to detect stomach cancer.
Treatment of some malignant tumors (cobalt–60 and cesium–137) cancer cells are more sensitive to radiation than normal, healthy cells
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Uses of Radiation X-rays Radioactive tracers: used in research
to tag chemicals to follow in living organisms
Everyday items: thorium–232 used in lantern mantels, plutonium–238 used in long-lasting batteries for space, and americium–241 in smoke detectors.