nuclear chemistry. atomic structure recall: atoms – consist of a positively charged nucleus,...
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Difference between the mass of an atom and the mass of its individual particles amu amu Mass Defect Nuclear ForcesTRANSCRIPT
NUCLEAR CHEMISTRY
Atomic StructureRecall:Atoms – consist of a positively charged nucleus, which has protons and neutrons.
Isotope Symbol # protons # neutrons
Atomic Mass
Mo-101H-2C-14U-238Bi-210He-4
H21
C146
U23892
Bi21083
He42
Mo10142 42
1692832
59181461272
101214238210 4
Isotope – atoms of the same chemical element that have a different number of neutrons. Each isotope of a given element is designated by the total number of its protons plus its neutrons.
• Difference between the mass of an atom and the mass of its individual particles.
4.00260 amu 4.03298 amu
Mass DefectNuclear Forces
Nuclear Binding Energy• Energy released when a nucleus is
formed from nucleons.• High binding energy = stable nucleus.
E = mc2E: energy (J)m:mass defect (kg)c: speed of light
(3.00×108 m/s)
Nuclear Binding Energy
Unstable nuclides are radioactive and undergo radioactive decay.
The seven most widely recognized magic numbers as of 2007 are 2, 8, 20, 28, 50, 82, 126
He42
Types of Radiation• Alpha particle ()
– helium nucleus paper2+
• Beta particle (-)– electron
e0-1 1-
lead
• Positron (+)– positron e0
1 1+
• Gamma ()– high-energy photon 0 concrete
ChargeShielding
00
Penetrating Ability of Radiation
Nuclear Decay
He Th U 42
23490
23892
e Xe I 0-1
13154
13153
e Ar K 01
3818
3819
Pd e Ag 10646
0-1
10647
•Transmutation-One element becomes another.
More than 83 protons means that the nuclei is unstable (radioactive)
Alpha Emission
He Th U 42
23490
23892
parentnuclide
daughternuclide
alphaparticle
Numbers must balance!!
occurs when the nucleus has too many protons which cause excessive repulsion.
Beta Emission
e Xe I 0-1
13154
13153
electron
occurs when the neutron to proton ratio is too great.
Neutron to Proton
XAZPo210
84
Ex. Polonium-210 undergoes beta decay to produce this daughter nuclide
+
Beta Emission
XAZ = At210
85
e01-
e Ar K 01
3818
3819
positron
Positron EmissionOccurs when the neutron to proton ratio is too small.
XAZPo210
84
Ex. Polonium-210 undergoes positron emission to produce this daughter nuclide
+
Positron Emission
XAZ = Bi210
83
e01
Electron Capture
Pd e Ag 10646
0-1
10647
electron
occurs when the neutron to proton ratio in the nucleus is too small.
XAZPo210
84
Ex. Polonium-210 captures an electron to produce this daughter nuclide
+
Electron Capture
XAZ = Bi210
83
e01-
Gamma Emission
– Emission of high energy electromagnetic wave.
occurs when the nucleus is at too high an energy.
XAZPo210
84
Ex. Polonium-210 undergoes gamma decay to produce this daughter nuclide
+
Gamma Emission
XAZ =
00
Po21084
Types of RadiationTypes of Radiation
Nuclear Fission– splitting of heavier nuclei into lighter nuclei.
U23592 n1
0 Ba13756 Xe84
36 n10
energy
+ +15+ +
How much energy? E=mc2
_______= _______ x (_____ _ _____)2 c=3.0x108Energy mass speed of light
E=mc2 explains _____ _____ (total mass of nucleus is less than sum of individual
particles)mass defect
Nuclear Fusion - Energy released when two light nuclei combine or fuse
•However, a large amount of energy is required to start a fusion reaction:
o Need this energy to overcome ________ forces of protons.o Extremely high temperatures can provide start-up energy.
repulsion
More energy in fusing hydrogen that fission of uranium
Nuclear Fusion
A A Decay Decay SeriesSeries
A radioactive nucleus reaches a stable A radioactive nucleus reaches a stable state by a series of stepsstate by a series of steps
Copyright© by Houghton Mifflin Company. All rights reserved.
27
Half-life ConceptHalf-life Concept
Decay KineticsDecay KineticsDecay occurs by first order kinetics (the rate of decay is proportional to the number of nuclides present)
ktNN
0
lnN = number of nuclides remaining at time t
N0 = number of nuclides present initially
k = rate constant
t = elapsed time
Calculating Half-lifeCalculating Half-life
kkt 693.0)2ln(
2/1
t1/2 = Half-life (units dependent on rate constant, k)
Sample Half-LivesSample Half-Lives
Half-lifen
if mm )( 21
mf: final massmi: initial massn: # of half-lives