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Chapter 22
Nuclear Chemistry

Radioactive decay
– An unstable isotope that undergoes
spontaneous disintegration of a nucleus into a
lighter nucleus (more stable)
Radioisotopes
Nuclei that undergo radioactive decay
 May produce one or more types of radiation

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Natural Radioactivity

Background
radiation
What occurs
from natural
sources
 >80% of
radioactivity
exposure

3
Types of Radiation

Ionizing radiation – knocks electrons out
of atoms or groups of atoms
Produces charged species – ions
 Charged species that cause damage

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Differences Between Chemical and
Nuclear Reactions
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Nuclear Equations
Elements may change in nuclear reactions
 Total mass and sum of atomic numbers
before and after must be the same
 MUST specify isotope

222
86
Rn  He 
4
2
218
84
Po
http://www.theodoregray.com/PeriodicTable/Posters/index.html
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Alpha Decay
Nucleus loses  particle
 Alpha particle will be on the right side of
the arrow


Mass decreases by 4 and atomic number
decreases by 2
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Beta Decay
Nucleus loses  particle
 Beta particle will be on the right side of
the arrow


No change in mass but atomic number
increases by one
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Electron Capture
Nucleus absorbs
an electron and
then releases an
X-ray
 Electron will be on
the left side of the
arrow
 Mass number
stays the same
and atomic number
decreases by one

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Positron Emission

Loses a positron
Equal mass but opposite charge of an
electron
 Decrease in atomic number by 1 and no
change in mass
 +

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Gamma Radiation

Release of highenergy photon




Typically occurs after
another radioactive
decay
No change in mass
number or atomic
number
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Nuclear Chemistry
Nuclear reaction – a reaction that affects the
nucleus of an atom
Nuclear radiation – particles or
electromagnetic radiation emitted from the
nucleus during radioactive decay
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Nuclear Chemistry

Nuclear equation
parent nuclide
222
86
daughter nuclide
Rn  He 
4
2
218
84
Po
Parent nuclide – the heaviest nuclide in a
decay series
Daughter nuclide – the nuclide produced by
the decay of the parent nuclide
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5/20/09 Bellwork (pg. 68)
Complete the following nuclear equations &
name the particle that goes in the blank.
14 C  14 N + _____
6
7
_______  4 He + 229 Th
2
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90
0
Mg  e- + _______
-1
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Nuclear Medicine
Used for two purposes
 Therapeutic – treat or cure disease using
radiation
 Diagnostic – obtain information about
patient’s health

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Uses of Radioisotopes
Tracers
 Radioactive atoms that are incorporated
into substances so that the movement of
the substance can be followed
 Many different isotopes used
 Can measure specific things

Iodine-131 to locate tumors in thyroid
 Selenium-75 to look at pancreas
 Gadolinium-153 to determine bone
mineralization

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Penetrating Power of Radiation
The more mass the particle has, the
less penetrating it is
 The faster the particle is, the more
penetrating it is

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Prevent Radiation Damage

To minimize
damage
Stay a distance
from radioactive
sources
 Use shielding;
need more with
more penetrating
forms of radiation

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Nuclear Fission



“Splitting the
atom”
Break a large
nucleus into
smaller nuclei
Produces
nuclei of lower
mass than the
reactants
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Nuclear Chain Reaction


Neutrons from
one fission event
split further
atoms
Only certain
isotopes, fissile
isotopes,
undergo nuclear
chain reactions
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Nuclear Power Plants

Provide ~20% U.S. electricity

France >70%
Slow controlled release of energy
 Need 2.5–3.5% 235U
 Problem with disposal of radioactive waste

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Nuclear Fusion

Reaction takes smaller nuclei and builds
larger ones

Also called thermonuclear reactions
4 H  He  2 e
1
1
4
2
0
1
• Releases tremendous amounts of energy
–1 g of H would release same as 20 tons of coal
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Detection Methods

Film Badges- worn by X-ray technicians

Use film exposure to measure radiation
exposure of people wearing the badge
Geiger-Muller counters- uses electric
impulses carried by gas
 Scintillation counters- convert light to an
electric signal

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Half-Life
Time it takes for onehalf of the original
elements to undergo
radioactive decay
 Characteristic for each
isotope

1
2n
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Radioisotopic Dating
Use certain isotopes to estimate the age
of various items
 235U
half-life = 4.5 billion years


Determine age of rock
3H


half-life = 12.3 years
Used to date aged wines
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Carbon-14 Dating




99.9% 12C
Produce 14C in upper
atmosphere
Half-life of 5730 years
~50,000 y maximum
age for dating
14
7
N n  C  H
1
0
14
6
1
1
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Half-Life
1. Phosphorus-32 has a half-life of 14.3
days. How many milligrams of phosphorus32 remain after 28.6 days if you start with
4.0 mg of the isotope?
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Problems
2. How many milligrams remain of a 15.0mg
sample of radium-226 after 6396 years? The
half-life of radium-226 is 1599 years.
Isotope name
Original amount
of isotope
Half-Life of
isotope
Number of
half-lives
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t
3. The half-life of radium-224 is 3.66 days.
What was the original mass of radium-224 if
0.0500g remains after 7.32 days?
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38
t
4. The half-life of radon-222 is 3.824 days.
After what time will 25% of a given amount of
radon remain?
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