Download lecture CH10 chem121pikul

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CHAPTER 10: Nuclear Chemistry
Learning Objectives:
! Interpret Atomic number and mass number
! Know radioactive particles: alpha, beta, positron,
gamma
! Write & solve radioactive decay equations
! Determine the number of half lives that pass in a
given amount of time.
! Familiar with measurements of the amount of
radioactivity
! Familiar with measurements of radiation absorbed
! Understand how radioisotopes are used in
medicine
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Nuclear
Chemistry
Isotope Review
atomic number (Z)
mass number (A)
mass number (A)
atomic number (Z)
=
the number of protons
=
the number of protons
+
the number of neutrons
12
6
C
number of protons
number of neutrons
6
12 – 6 = 6
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Nuclear
Chemistry
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Radioactive Isotopes
• A radioactive isotope, called a radioisotope, is
unstable and spontaneously emits energy to form
a more stable nucleus.
• Radioactivity is the nuclear radiation emitted by a
radioactive isotope.
• Of the known isotopes of all elements, 264 are
stable and 300 are naturally occurring but unstable.
• An even larger number of radioactive isotopes,
called artificial isotopes, have been produced in
the laboratory.
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Nuclear
Chemistry
Radiation
alpha particle: !
4
He
2
or
beta particle:
! or 0 e
"1
positron: !+
or
0
e
+1
"
gamma ray:
" Alpha particles are helium isotopes
with 2 extra neutrons
" Beta particles are formed from neutrons
1
1
0
n
p +
e
0
1
!1
proton # particle
neutron
" Positrons are formed from protons
1
0
1
n +
e
p
0
+1
1
neutron positron
proton
" A form of energy with no mass or charge
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Nuclear
Chemistry
Nuclear Reactions
Radioactive decay is the process by which an
unstable radioactive nucleus emits radiation.
A nuclear equation can be written as:
original
nucleus
new
nucleus
+
radiation
emitted
The following must be equal on both sides of a
nuclear equation :
• The sum of the mass numbers (A)
• The sum of the atomic numbers (Z)
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Nuclear
Chemistry
Nuclear Reactions
Alpha emission is the decay of a nucleus
by emitting an ! particle.
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Nuclear
Chemistry
B(
Nuclear Reactions
Beta emission is the decay of a nucleus by emitting
a " particle; 1 neutron is lost and 1 proton is gained.
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Nuclear
Chemistry
Nuclear Reactions
Positron emission is the decay of a nucleus by emitting
a positron, "+; 1 proton is lost and 1 neutron is gained.
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Nuclear
Chemistry
Nuclear Reactions
Gamma emission is the decay of a nucleus by emitting
" radiation.
• The " rays are a form of energy only.$
• Their emission causes no change in the atomic
number or the mass number.
99m
43 Tc
99
43 Tc
+
"$
Commonly, "
emission
accompanies !
or " emission.
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Nuclear
Chemistry
Half-Life
The half-life (t1/2) of a radioactive isotope is the time it
takes for one-half of the sample to decay.
The half-life of a radioactive isotope is a property of a
given isotope and is independent of the amount of
sample, temperature, and pressure.
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Nuclear
Chemistry
EE(
Half-Life
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Nuclear
Chemistry
Detecting & Measuring Radioactivity
The amount of radioactivity in a sample is measured by the
number of nuclei that decay per unit time: disintegrations per sec.
• Common units include:
1 Curie (Ci) = 3.7 x 1010 disintegrations/second
1 becquerel (Bq) = 1 disintegration/second
1 Ci = 3.7 x 1010 Bq.
Several units are used to measure the amount of
radiation absorbed by an organism.
• The rad—radiation absorbed dose—is the amount of radiation
absorbed by one gram of a substance.
• The rem—radiation equivalent for man—is the amount of radiation that
also factors in its energy and potential to damage tissue.
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Nuclear
Chemistry
E>(
Detecting & Measuring Radioactivity
• The average radiation dose per year for a person
is about 0.27 rem.
• Generally, no detectable biological effects are
noticed for a radiation dose less than 25 rem.
• A single dose of 25–100 rem causes a temporary
decrease in white blood cell count.
• A dose of more than 100 rem causes radiation
sickness—nausea, vomiting, fatigue, etc.
• The LD50—the lethal dose that kills 50% of a
population—is 500 rem in humans, while 600
rem is fatal for an entire population.
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Nuclear
Chemistry
Radioisotopes Used in Medicine
• Radioisotopes can be injected or ingested to
determine if an organ is functioning properly or
to detect the presence of a tumor.
• Technetium-99m is used to evaluate the gall
bladder and bile ducts and to detect internal
bleeding.
• Thallium-201 is used in stress tests to diagnose
coronary artery disease.
• Using a scan, normal organs are clearly visible,
while malfunctioning or obstructed organs are not.
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Nuclear
Chemistry
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Radioisotopes Used in Medicine
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Nuclear
Chemistry
Radioisotopes Used in Medicine
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Nuclear
Chemistry
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Radioisotopes Used in Medicine
• Positron emission tomography (PET) scans use radioisotopes
which emit positrons which enable scanning of an organ.
• PET scans can detect tumors, coronary artery disease,
Alzheimer’s disease, and track the progress of cancer.
• A PET scan is a noninvasive method of monitoring cancer
treatment.
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