CHAPTER 28 Nuclear Chemistry Radioactive Decay Radioactive Decay.
Nuclear Decay
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Transcript of Nuclear Decay
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Nuclear DecayOctober 15nd & 16th, 2009
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The Atom- Review•The atom consists of two parts:
1. The nucleus which contains:
2. Orbiting electrons.
protons
neutrons
•Atom of different elements contain different numbers of protons.
•The mass of an atom is due to the number of protons and neutrons.
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XAZ
Mass number
Atomic number
Element symbol
= number of protons + number of neutrons
= number of protons
Isotope Symbol Review
A = number of protons + number of neutrons
Z = number of protons
A – Z = number of neutrons
**Number of neutrons = Mass Number – Atomic Number**
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U235
92U
238
92
Fill in the chart for each isotope
A
Z
Number of protons
Number of neutrons
A
Z
Number of protons
Number of neutrons
235
92
92
143
92
92
238
146
Isotopes of any particular element contain the same number of protons, but different numbers of neutrons.
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•Most of the isotopes which occur naturally are stable.
•A few naturally occurring isotopes and all of the man-made isotopes are unstable.
•Unstable isotopes can become stable by releasing different types of particles.
•This process is called radioactive decay and the elements which undergo this process are called radioisotopes.
•The products of this decay are called daughter isotopes
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Radioactive decay results in the emission of either:
• an alpha particle (),
• a negative beta particle (electron) (),
• or a gamma ray
Radioactive Decay
• a positive beta particle (positron) (),
In a nuclear reaction the MASS and ATOMIC NUMBER must be the SAME on both sides of the equations
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An alpha particle is identical to that of a helium nucleus.
It contains two protons and two neutrons.
Alpha Decay
XA
ZY
A - 4
Z - 2+ He
4
2
unstable atom
more stable atom
alpha particle
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Alpha Decay
Ra226
88Rn
222
86 He4
2+
Loss of 2 protons & 2 neutrons: Atomic # decreases by 2Mass # decreases by 4
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XA
ZY
A - 4
Z - 2+ He
4
2
Write your own Alpha Decay
Rn222
86+Y
A
ZHe
4
2
What is Y?
Rn222
86He
4
2+Po
218
84He
4
2
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U234
+
Write the equation for the alpha decay of Uranium-234
He4
2U
234
92+Th
230
90He
4
2
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X A
Z+Pb
214
82He
4
2
Find the missing starting material
He4
2+Pb
214
82He
4
2Po
218
84
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Beta EmissionA beta particle is a fast moving electron which is emitted from the nucleus of an atom undergoing radioactive decay.
Beta emission occurs when a neutron changes into a proton and an electron.
XA
ZY
A
Z + 1+ e
0
-1
beta particle (electron)
proton stays in nucleus
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Beta Emission
Po218
84e
0
-1At
218
85+
Neutron splits emitting negative particle leaving a proton.•Atomic # increases by 1 •Mass # stays the same
(electrons have no mass)
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XA
ZY
A
Z + 1+ e
0
-1
Write your own Beta Emission
What is Y?
Th234
90Y
A
Z+ e
0
-1
Th234
90Pa
234
91+ e
0
-1
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C 14
+
Write the equation for the betaemission of carbon-14
C14
N14
7+ e
0
-1
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X A
ZBi
214
83+ e
0
-1
Find the missing starting material
Pb214
82Bi
214
83+ e
0
-1
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Electron Capture is the opposite of Beta Emission
Electron Capture
XA
Ze
0
-1+ Y
A
Z-1
The capture of the electron allows a proton to turn into a neutron
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Electron Capture
Po218
84e
0
-1
At218
85+
Capture negative particle, forming a neutron from a proton•Atomic # decreases by 1 •Mass # stays the same
(electrons have no mass)
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Write your own Electron Capture
What is Y?
XA
Ze
0
-1+ Y
A
Z-1
Ar37
18e
0
-1+ Y
A
Z-1
Ar37
18e
0
-1+ Cl
37
17
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Ni 59
+
Write the equation for electroncapture of nickel-59
Ni59
28e
0
-1+ Co
59
27
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Find the missing starting material
XA
Ze
0
-1+ C
14
6
N14
7e
0
-1+ C
14
6
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Positron EmissionA positron is like an electron but it has a positive charge.
During positron emission a proton changes into a neutron and the excess positive charge is emitted.
XA
ZY
A
Z - 1+ e
0
+1
positronmass stays in nucleus
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Positron Emission
Po218
84 e0
+1
At218
85+
Proton splits emitting positive particle leaving a neutron.•Atomic # decreases by 1 •Mass # stays the same
(positrons, like electrons, have no mass)
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XA
ZY
A
Z - 1+ e
0
+1
Write your own Positron Emission
What is Y?
B8
5Y
A
Z+ e
0
+1
B8
5Be
8
4+ e
0
+1
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O 16
+
Write the equation for the positronemission of oxygen-16
O16
N16
7+ e
0
+1
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X A
ZCu
66
29+ e
0
+1
Find the missing starting material
Zn66
30Cu
66
29+ e
0
+1
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Gamma Decay
•Gamma rays are not charged particles like and particles.
•Gamma rays are high energy radiation
•When atoms decay by emitting or particles to form a new atom, the nuclei of the new atom formed may still have too much energy to be completely stable. These atoms will emit gamma rays to release that energy.
•There is no change in mass or atomic number
XA
ZX
A
Z + 0
0
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SummaryReaction What happens? Mass # Atomic #
Alpha Decay
Lose Helium Nucleus -4 -2
Beta Decay -
Lose electron from nucleus(neutron turns into proton)
No change +1
Electron Capture Gain electron in nucleus (proton turns into neutron)
No change -1
Positron Emission
Lose positron (proton turns into neutron)
No change -1
Gammy Decay
Emit high energy gamma ray No change No change
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Nuclear Stability The strong nuclear force holds all nuclei together
Otherwise protons would repel each other Neutrons space out protons and make nucleus stable
Not all isotopes are radioactive
Only unstable nuclei decay
In smaller atoms stable isotopes have equal numbers of protons and neutrons
In larger atoms stable isotopes will have more neutrons than protons
Too many or too few neutrons makes the nucleus unstable
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Nuclear Stability Graph
Dark band = stable nucleusAreas off line = radioactive
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Fission
Fission is when a nucleus splits This is what happens in nuclear
power plants
Neutrons emitted during fission reactions can cause other fission reactions This is a chain reaction
In a nuclear reactor the chain reaction is controlled with control rods
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Chain Reaction
Each reaction allows multiple other reactions to occur
Controlled vs Uncontrolled
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Fusion
When two or more elements fuse (combine) to form one new heavier element
The energy released by the sun and all stars is due to fusion reactions in the core
This process releases more energy than fission
Fusion reactions are hard to contain because the reactants are a plasma and at very high temperatures, no solid material can contain a plasma
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Fission Fusion
Nuclei combineNucleus splits
End product is heavier than reactants
End product is lighter than reactants
Energy is released
LOTS of energy released
Can’t contain reaction
Reaction can be harnessed
Nuclear Change