1 NUCLEAR CHEMISTRY. 2 Isotopes Same element (Z) but different mass number (A).Same element (Z) but...
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Transcript of 1 NUCLEAR CHEMISTRY. 2 Isotopes Same element (Z) but different mass number (A).Same element (Z) but...
1
NUCLEAR CHEMISTRY
2IsotopesIsotopes
• Same element (Same element (ZZ) but different mass ) but different mass number (number (AA).).
• Boron-10Boron-10 has has 5 p5 p and 5 n: and 5 n: 101055BB
• Boron-11Boron-11 has has 5 p5 p and 6 n: and 6 n: 111155BB
10B
11B
3IsotopesIsotopes• Hydrogen: Hydrogen:
– 1111H, protiumH, protium
– 2211H, deuteriumH, deuterium
– 3311H, tritium H, tritium
(radioactive)(radioactive)
• Helium, Helium, 4422HeHe
• Lithium, Lithium, 6633Li Li
and and 7733LiLi
• Boron, Boron, 101055B B
and and 111155BB
• Except for Except for 1111H the mass H the mass
number is always at least 2 number is always at least 2
x atomic number. x atomic number.
• Repulsive forces between Repulsive forces between
protons must be protons must be
moderated by neutrons.moderated by neutrons.
4ATOMIC COMPOSITIONATOMIC COMPOSITION
• ProtonsProtons– + electrical charge+ electrical charge– mass = 1.672623 x 10mass = 1.672623 x 10-24-24 g g– relative mass = 1.007 atomic mass units relative mass = 1.007 atomic mass units
(amu)(amu)• ElectronsElectrons
– negative electrical chargenegative electrical charge– relative mass = 0.0005 amurelative mass = 0.0005 amu
• NeutronsNeutrons– no electrical chargeno electrical charge– mass = 1.009 amumass = 1.009 amu
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RadioactivityRadioactivity
• One of the pieces of evidence for One of the pieces of evidence for the fact that atoms are made of the fact that atoms are made of smaller particles came from the smaller particles came from the
work of work of Marie CurieMarie Curie (1876- (1876-1934). 1934).
• She discovered She discovered
radioactivityradioactivity, the , the spontaneous disintegration of some spontaneous disintegration of some elements into smaller pieces.elements into smaller pieces.
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RadioactivityRadioactivity Emission of particles and/or
energy due to a change in the nucleus of an atom.
Nuclear Radiation also called Ionizing radiation
Measure with Geiger Counter
7Geiger Counter: Geiger Counter:
Radiation detectionRadiation detection
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Types of NUCLEAR Types of NUCLEAR RadiationRadiation
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Nuclear ReactionsNuclear Reactions
• Ernest Rutherford found Ra forms Rn gas
when emitting an alpha particle.
• 1902—Rutherford and Soddy proposed
radioactivity is the result of the natural
change of the isotope of one element into
an isotope of a different element.
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Nuclear ReactionsNuclear ReactionsorTransmutationsorTransmutationsNatural Decay
Spontaneous breakdown of unstable nuclei.
Called Radioisotopes
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Penetrating AbilityPenetrating Ability
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NATURAL Decay:NATURAL Decay:
DECAY = Fall apartAlpha DECAYBeta DECAY
Positon DECAY
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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 are rearranged but conserved [mass number (A)]
Nucleons = PROTON OR NEUTRON (particle in the nucleus)
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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.
How does this happen?
15Other Types of Nuclear Other Types of Nuclear ReactionsReactions
Positron (Positron (00+1+1): a positive electron): a positive electron
K-capture:K-capture: the capture of an electron from the first or K shell
An electron and proton combine to form a neutron.0
-1e + 11p --> 1
0n
207 207
16Radioactive Decay SeriesRadioactive Decay Series
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Writing Nuclear Reactions Parent element = Reactant
Daughter element = Product
Radioactivity = radiation produced
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Writing Nuclear Reactions
Law of Conservation of Mass
L. of C. of Charge Isotopic Notation Mass # and Nuclear Charge
146C = 14
7N + 0-1e
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21Stability Stability of of NucleiNuclei
• Heaviest naturally Heaviest naturally
occurring non-radioactive occurring non-radioactive
isotope is isotope is 209209Bi with 83 Bi with 83
protons and 126 neutronsprotons and 126 neutrons
• There are 83 x 126 = There are 83 x 126 =
10,458 possible isotopes. 10,458 possible isotopes.
Why so few actually exist?Why so few actually exist?
22Band of Stability Band of Stability and Radioactive and Radioactive DecayDecay 243
95Am --> 42 + 239
93Np
emission reduces Z
emission increases Z
6027Co --> 0
-1 + 6028Ni
Isotopes with low n/p ratio, below band of stability decay, by positron emission or electron capture
23Stability 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
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Binding Energy, EBinding Energy, Ebb
EEbb = energy required to separate the = energy required to separate the
nucleus into protons and neutronsnucleus into protons and neutrons..
For deuterium, For deuterium, 2211HH
2211H ---> H ---> 11
11p + p + 1100nn EEbb = 2.15 x 10 = 2.15 x 1088 kJ/mol kJ/mol
EEbb per nucleon per nucleon = = EEbb //2 2 nucleonsnucleons
= 1.08 x 10= 1.08 x 1088 kJ/mol nucleons kJ/mol nucleons
25Binding Binding Energy/NucleonEnergy/Nucleon
26Calculate Binding Calculate Binding EnergyEnergy
For deuterium, For deuterium, 2211H: H: 22
11H ---> H ---> 1111p + p + 11
00nn
Mass of Mass of 2211H = 2.01410 g/molH = 2.01410 g/mol
Mass of proton = 1.007825 g/molMass of proton = 1.007825 g/mol
Mass of neutron = 1/008665 g/molMass of neutron = 1/008665 g/mol
∆∆m = 0.00239 g/molm = 0.00239 g/mol
From Einstein’s equation: From Einstein’s equation:
EEbb = (∆m)c = (∆m)c22 = 2.15 x 10 = 2.15 x 1088 kJ/mol kJ/mol
EEbb per nucleon = E per nucleon = Ebb/2 nucleons /2 nucleons
= 1.08 x 10= 1.08 x 1088 kJ/mol nucleons kJ/mol nucleons
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Half-LifeHalf-LifeSection 15.4 & Screen 15.8Section 15.4 & Screen 15.8
• HALF-LIFEHALF-LIFE is the time it takes for 1/2 a is the time it takes for 1/2 a sample is disappear.sample is disappear.
• The rate of a nuclear transformation depends The rate of a nuclear transformation depends only on the “reactant” concentration.only on the “reactant” concentration.
• Concept of HALF-LIFE is especially useful for Concept of HALF-LIFE is especially useful for 1st order reactions.1st order reactions.
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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?
29Kinetics of Radioactive Kinetics of Radioactive DecayDecay
Activity (A) = Disintegrations/time = (k)(N)
where N is the number of atoms
Decay is first order, and so
ln (A/Ao) = -kt
The half-life of
radioactive decay is
t1/2 = 0.693/k