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Chapter 23: Nuclear Chemistry
• Nuclear Changes
• Nuclear Equations
•
238 U
92
 23490Th + 42He
Chapter 23: Nuclear Reactions & the
Nucleus
• Nucleons: particles in the nucleus:
– p+: proton
– n0: neutron.
– Mass number: the number of p+ + n0.
• Isotopes: have the same number of p+ and different
numbers of n0.
• Nuclear Binding Energy
– Mass Defect
Chapter 23: Energy Versus Mass
• Energy and Mass are interchangable.
• Law of Conservation of Mass and Law of
Conservation of Energy are the same.
– Sum of all energy and all mass is a constant.
• Nuclear Binding Energy
– Mass Defect
Balancing Nuclear Equations
• In nuclear equations, the total number of
nucleons is conserved:
238 U  ? + 4 He
92
2
Chapter 23: Radioactivity
• Isotopes: have the same number of p+ and
different numbers of n0.
• Stable
• Radioisotopes
– Natural
– Manmade
Radiosotopes: Radioactivity
• Definition
• The three primary types of radioactivity are:
– -Radiation is the loss of 42He from the nucleus,
– -Radiation is the loss of an electron from the nucleus,
– -Radiation is the loss of high-energy photon from the
nucleus.
Radioactivity
Nuclear Equations
Radioactivity: Types of radioactive Decay
• Alpha Particles/Alpha Emission:
•
4 He
2
and 42 represent -radiation.
– 23892U  23490Th + 42He
Radioactivity: Types of radioactive
Decay
• Beta Particles/Beta Emission:
• Nucleons undergoes decay:
1 n  1 p+ + 0 e- (-emission)
0
1
-1
0 e- + ______
C

6
-1
14
Radioactivity: Gamma Emission
• Electromagnetic Energy
• Spectrum
• Can be emitted with Particles
Additional Types of Nuclear
Decay: Decay Equations
Positron Emission
1 p+  1 n + 0 e+ (positron or +0
0
1
emission)
• A positron is a particle with the
same mass as an electron but a
positive charge.
Additional Types of Nuclear
Decay: Decay Equations
ELECTRON CAPTURE
+ + 0 e-  1 n (electron capture)
p
1
-1
0
1
7
0 e-  ______
Be
+
4
-1
Radioactive Series
• A nucleus usually undergoes more than one
transition/decay on its path to stability.
• The series of nuclear reactions that accompany
this path is the radioactive series.
• Nuclei resulting from radioactive decay are called
daughter nuclei.
Patterns of Nuclear Stability
Radioactive Series
For 238U, the first decay is to
234Th (-decay). The 234Th
undergoes -emission to
234Pa and 234U. 234U
undergoes -decay (several
times) to 230Th, 226Ra, 222Rn,
218Po, and 214Pb. 214Pb
undergoes -emission
(twice) via 214Bi to 214Po
which undergoes -decay to
210Pb. The 210Pb undergoes
-emission to 210Bi and
Chapter 23: Nuclear Reactions:
Nuclear Transmutation
Target + Particle  Products
14N
+ 4  17O + 1p.
• The above reaction is written in shorthand notation:
14N(,p)17O.
Nuclear Transmutations
Using Charged Particles
Chapter 22: Nuclear ReactionsNuclear Fission
• Consider a neutron bombarding a 235U nucleus:
Nuclear Fission
• During fission, the incoming neutron must move
slowly because it is absorbed by the nucleus,
• The heavy 235U nucleus can split into many
different daughter nuclei, e.g.
1 n + 238 U  142 Ba + 91 Kr + 31 n
0
92
56
36
0
releases 3.5  10-11 J per 235U nucleus.
• For every 235U fission 2.4 neutrons are produced.
• Each neutron produced can cause the fission of
another 235U nucleus.
Nuclear Fission
Chapter 22: Nuclear Reactions-Nuclear
Fusion
• Light nuclei can fuse to form heavier nuclei.
• . 21H + 31H  42He + 10n
• Fusion products are not usually radioactive, so
fusion is a good energy source.
• High energies are achieved by high temperatures:
the reactions are thermonuclear.
Chapter 23: Rates of Radioactive
Decay: Half-Life (t1/2)
• Definition
• Multiple Half-Lives
Chapter 23: Rates of Radioactive
Decay: Half-Life (t1/2)
• Definition
• Multiple Half-Lives
Chapter 23: Rates of Radioactive
Decay: Half-Life (t1/2)
• Twenty Micrograms of a
radioisotope exists at time zero.
t1/2 = 12 hours. How much of this
radioisotope remains after 12
hours, 24 hours, 36 hours, 48
hours?
Rates of Radioactive Decay
Rates of Radioactive Decay
Rates of Radioactive Decay: Half-Life
(t1/2)
• Each isotope has a characteristic half-life.
• Half-lives are not affected by temperature,
pressure or chemical composition.
• Natural radioisotopes tend to have longer halflives than synthetic radioisotopes.
Rates of Radioactive Decay: Half-Life
(t1/2)
• Half-lives can range from fractions of a second to
millions of years.
• Naturally occurring radioisotopes can be used to
determine how old a sample is.
• This process is carbon/radioactive dating.
Calculation of Half-Life
• Radioactive decay is a first order process:
Rate = kN
• The rate of decay is called activity (disintegrations
per unit time).
• If N0 is the initial number of nuclei and Nt is the
number of nuclei at time t, then
Nt
ln
  kt
N0
Calculation of Half-Life
Ln [A]= (-kt) + ln Aº / At
Half-Life Calculations
• First Order Rate Constant is Related to Half Life
k
0.693
t1
2
Rates of Radioactive Decay
Carbon Dating
• For us to detect 14C the object must be less
than 50,000 years old.
• The half-life of 14C is 5,730 years.
• We assume the ratio of 12C to 14C has been
constant over time.
• It undergoes decay to 14N via -emission:
14 C 14 N + 0 e
6
7
-1
Problem
• A wooden artifact from a Chinese temple
has a 14C activity of 24.9 counts per minute
(CPM) as compared with an activity of 32.5
CPM for a standard of zero age. From the
half-life of 14C decay, 5715 years,
determine the age of the artifact.
Problem 21.37
th
(9
Edition)
• t= 3.3232 (t1/2) log Nº / Nt
• (t1/2) = 5715 years
• Nº = 32.5 cpm
• Nt = 24.9 cpm
• time/age = 2.20E3 years
Example 23.1, Page 969
• Balance the following nuclear equations and
identify X
•
212Po
 208 Pb + X
•
137Cs
 137Ba + X
Detection of Radioactivity
• Matter is ionized by radiation.
• Geiger counter determines the amount of
ionization by detecting an electric current.
• A thin window is penetrated by the radiation and
causes the ionization of Ar gas.
• The ionized gas carried a charge and so current is
produced.
• The current pulse generated when the radiation
enters is amplified and counted.
Detection of Radioactivity
Chapter 22: Mass-Energy
Conversions in Nuclear Reactions
• Einstein showed that mass and energy are
proportional:
E = mc2
• If a system loses mass it loses energy
(exothermic).
• If a system gains mass it gains energy
(endothermic).
E=
2
mc
• Since c2 is a large number (8.99  1016
m2/s2) small changes in mass cause large
changes in energy.
• Mass and energy changed in nuclear
reactions are much greater than in
nonnuclear/chemical reactions.
Chapter 22: Energy Changes in
Nuclear Reactions
Nuclear Binding Energies
• The mass of a nucleus is less than the mass of
their nucleons.
• Mass defect is the difference in mass between the
nucleus and the masses of nucleons.
Calculation of Binding Energy
• Binding energy is the energy required to
separate a nucleus into its nucleons.
• ∆E = ∆mc2
c=2.99792458E8 meters/seconds
Calculation of Binding Energy
MUST CONNECT MASS CHANGES
TO ENERGY
KINETIC ENERGY=1/2 (MASS VELOCITY)2
• Joule = kg (m2/second2)
Problem
• Calculate the binding energy per nucleon
for the following nuclei.
• (a) 126C (nuclear mass = 11.996708 amu)
• Proton = 1.0072765 amu
• Neutron = 1.0086649 amu
• Amu = 1.66053873E-24 grams
Problem
• Joule = kg (m2/second2)
• Calculated mass = [(6) (1.0072765 amu) +
(6) (1.0086649 amu)] =
• Mass defect = calculated mass – actual
mass =
Energy Changes in Nuclear Reactions
Nuclear Binding Energies
Binding Energy: Units
• The energy carried by radiation is usually
given in electron volts (eV)
• 1 eV is the energy an electron receives
when accelerated under the influence of 1
volt
• It is related to the joule as:
• 1 eV = 1.602E-19 Joules
Recognition of Radisotopes:
Nuclear Stability
14C, 12C, 13C
• Look for neutron/protron ratio
• Look for magic numbers
• Or, Refer to A Belt of Stability
Recognition of Radioistopes:
Neutron/Proton Ratio
• If N/P ratio = 1, probably stable.
• If N/P ratio < 1, maybe radioactive
– Positron Emission
– Electron Capture
If N/P ration > 1, maybe radioactive
Probably Beta Emitter
Recognition of Radioisotopes:
Neutron/Proton Ratio
• Elements with Atomic Number of 83
or higher are usually radioactive.
– Alpha, and Gamma Emitters
Recognition of Radioisotopes:
Magic Numbers
Isotopes with specific numbers of protons or
neutrons are more stable than the rest
• The magic numbers are: 2, 8, 20, 28, 50, 82,
and 126
• Magic numbers do not cancel the need for a
favorable neutron:proton ratio
4He
16O
208Pb
• Magic numbers supports the hypothesis that a nucleus has a
shell structure with energy levels like those for electrons
Recognition of Radioisotopes:
Band/Belt of Stability
• Band/Belt of Stability will be
provided.
• Most Reliable method
• Isotopes with atomic number greater than 83
tend to be alpha emitters
• Their nuclei have too many protons. The most
efficient way to lose protons is by the loss of an
alpha particle.
• Isotopes occurring above and to the left of the
band of stability tend to be beta emitters
• The neutron:proton ration is apparently too high.
A nucleus that undergoes beta decay loses a
neutron and gains a proton which reduces the
ratio. For example, beta decay by fluorine-20
decreases the neutron:proton ratio from 11/9 to 10/10.
The band of stability. A
1:1 ratio of neutrons to
protons is indicated by
the straight line.
The band of stability
curves away from this.
More protons require
more neutrons to provide
a compensating nuclear
strong force and to dilute
the electrostatic protonproton repulsions.
• Isotopes lying below and to the right of the band
are positron emitters
• These nuclei have too few neutrons to be
stable.
• Positron emission increases the
neutron:proton ratio.
– For example, a fluorine-17 has a
neutron:proton ratio of 8/9. Positron emission
converts it into oxygen-17, an isotope in the
band of stability with a neutron:proton ratio of
9/8.
Recognition of Radioisotopes
Band/Belt of Stability
• Isotopes lying below and to the right of the band are
positron emitters
• These nuclei have too few neutrons to be stable.
• Positron emission increases the neutron:proton
ratio.
– For example, a fluorine-17 has a neutron:proton
ratio of 8/9. Positron emission converts it into
oxygen-17, an isotope in the band of stability with a
neutron:proton ratio of 9/8.
Biological Effect of Radioactivity
• The radiation can generate very reactive
species with unpaired electrons called
free radicals or simply radicals
• target + radioactivity  free radicals
• Once the radicals are generated, they can
start a chain of undesirable chemical
events
Terms Used to Measure Exposure to
Radioactivity
• Must measure rate of radioactivity
production.
• Must Also Measure Energy Deposited by
Radioactivity.
• Must Also Measure Biological Damage.
• The curie (Ci), named after Marie Curie, is
an older unit equal to the activity of a 1.0 g
sample of radium-226
1
1 Ci  3.7 10 disintegra tions s  3.7 10 Bq
10
10
• SI Equivalent Unit is the Becquerel (Bq).
• Bq = one disintegration per second
• 1 Ci = 3.7E10 Bq
• The energy equivalent to the quantity of radiation
absorbed by some material is defined in units of
absorbed dose or simply dose
• The SI unit of absorbed dose is the gray (Gy)
• 1 Gy = 1 J of energy absorbed per kg of
material
• The Radiation Absorbed Dose or rad is an
older unit
• 1 rad = 0.01 Gy
• A different unit is used for measuring the biological effects
of radiation because the effects depend on the type and
energy of the radiation
• The sievert (Sv) is the SI unit of dose equivalent, H
• The dose equivalent (in Sv) is a product of the
absorbed dose (D) from some radiation source
times a factor (Q) that takes into account the
biologically significant properties times any other
factor (N) bearing on the net effect
• The rem is an older unit for dose equivalent:
1 rem = 0.01 Sv
• A typical X-ray involves about 0.007 rem
– A whole body dose of 25 rem (0.25 Sv) induces
noticeable changes in blood
– A set of symptoms called radiation sickness
develops at about 100 rem, and becomes severe
at about 200 rems
• Symptoms include: nausea, vomiting, a drop in
white blood count, diarrhea, dehydration,
prostration, hemorrhaging, and loss of hair
– If everyone in a large group received 400 rem,
half would die in 60 days
– 600 rem would kill everyone within a week
• Natural and man made sources of radiation
contribute to a combined background
radiation total of about 360 mrem per
person per year
• About 82% of the background radiation is from
natural sources and the remaining 18% from
medical sources (much in the form of X-rays)
• Radiation sources should be avoided
because the intensity of radiation diminishes
as 1/(distance from a source)2
Problem 23.6-C: Page 1017
• Complete the following nuclear equation
and identify X.
1 n 
Co
+
27
0
59
56
25Mn
+ X
Problem 23.14-A, B: Page 1017
• For each pair of isotopes listed, predict
which one is less stable.
(A) 63Li or 93Li
(B) 2311Na or 2511Na
Problem 23.34-A: Page 1018
• Write a balanced nuclear equation for the
following reaction and identify X.
d (deuterium) is 21H
(A)
80 Se(d,
34
p)X
Problem 23.36: Page 1018
• A long cherished dream of alchemists was
to produce gold from cheaper and more
abundant elements. This dream was finally
realized when 19880Hg was converted into
gold by nuclear bombardment. Write a
balanced equation for this reaction.
Problem 23.86: Page 1020
• A 0.0100 gram sample of a radioactive
isotope with a half-life of 1.3E9 years
decays at the rate of 2.9E4 dpm. Calculate
the molar mass of the isotope.
Strategy: 23.86
• Have number of grams. Need number of moles.
• Calculate value of k. Since the unit of this rate
are DP minute (DPM), convert t1/2 to minutes
• Substitute in: Rate = k N
– “N” can be number of Nuclei
– Calculate “N”
– Use Avogardo’s number to convert value of “N” to
moles.
– 0.0100 grams/calculated number of moles
Problem 23.95-A: Page 1021
• In 2006, an ex-KGB agent was murdered in
London. Subsequent investigation showed
that the cause of death was poisoning with
the radioactive isotope 210Po, which was
added to his drinks/food.
(A) 210Po is prepared by bombarding 209Bi
with neutrons. Write the equation for this
reaction
Problem 23.95-D: Page 1021
• In 2006, an ex-KGB agent was murdered in London.
Subsequent investigation showed that the cause of death was
poisoning with the radioactive isotope 210Po, which was added
to his drinks/food.
(D) t1/2 = 138 d and decays by alpha emission.
Calculate the energy of an emitted alpha
particle. Assume both the parent and daughter
nuclei to have zero kinetic energy. The atomic
masses are: 210Po (209.9825 amu); 206Pb
(205.97444 amu) ; 42α (4.00150 amu)
Strategy: 23.86 D
• Need mass defect: ∆m = final – initial
• Δm = (mass 206Pb + mass α) − mass 210Po
• ∆E = (Δm) C2
Calculated value of ∆E represents value of alpha
particle since it is only on the reactant side
∆E = 1.04E-12 J
Problem 23.95-E: Page 1021
In 2006, an ex-KGB agent was murdered in
London. Subsequent investigation showed
that the cause of death was poisoning with
the radioactive isotope 210Po, which was
added to his drinks/food.
(E) Ingestion of 1 µg of 210Po could prove
fatal. What is the total energy released by
this quantity of 210Po?
Strategy: 23.86 E
• The energy calculated in part (d) is for the emission
of one α particle. The total energy released in the
decay of 1μg of 210Po is:
(1.0E-6 g 210Po) (mole 210Po /209.98285 g) (1 mole α
/mole 210Po)
(6.022E23 α particles/1 mole α)
(1.04E-12 J/1 α particle
= 2.98E3 J