Nuclear Chemistry
The study of
changes to the
nucleus of the
atom.
The Nucleus
Comprised of protons and neutrons (nucleons).
# protons = atomic number.
# protons + neutrons = mass number
Isotope Review
Isotope:
Atoms of the same element with different numbers of neutrons.
 Have different levels of “abundance” in nature.
 Some isotopes or “nuclides” of an element can be
unstable, or “radioactive”.

Example of Carbon Isotopes
Note:
We will be talking about isotopes very specifically in this unit. We will not be
using the average atomic mass you see on the Ref tables.
What is Radioactivity?

Radioactivity: the “decay” of the nucleus
by emitting particles and/or energy in order
to become more stable.
What Causes an Isotope to be
Radioactive and Decay?
Proton : Neutron
ratio in nucleus
Neutron-Proton Ratios

Positive protons in the
nucleus repel each other.

Neutrons play a key role
stabilizing the nucleus.
Neutron-Proton
Ratios
For smaller nuclei
(atomic # below 20)
stable nuclei have a
neutron-to-proton
ratio close to 1:1.
Neutron-Proton
Ratios
As nuclei get
larger, it takes a
greater number of
neutrons to
stabilize the
nucleus.
There are no stable nuclei
with an atomic number
greater than 83.
Early Pioneers in Radioactivity
Rutherford:
Roentgen:
Discoverer
Alpha and Beta
rays 1897
Discoverer of
X-rays 1895
The Curies:
Discoverers of
Radium and
Polonium 19001908
Marie Curie 3 parts 7 minutes each
http://www.youtube.com/watch?v=Uaiq-eus-c0&safe=active
http://www.youtube.com/watch?v=eDRk1gTvg30&safe=active
http://www.youtube.com/watch?v=BIIC2KYoAEo&safe=active
Becquerel:
Discoverer of
Radioactivity
1896
RUTHERFORD DESCOVERS
DIFFERENT TYPES OF
RADIATION
Ernest Rutherford discovered three
types of radioactive emissions by
using a magnetic field.
Reference Table O

Shows the symbols
of some of the
different particles
used in nuclear
chemistry.

Top # = mass
Bottom # = charge

Types of
Radioactive Decay
http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/radioa7.swf
Cloud Chamber: https://www.youtube.com/watch?v=chxv5G6UFl0
Alpha Decay
An -particle is emitted (basically a helium nucleus)
4
2
238
92
U
He

234
90
4
2
Th+ He
Heaviest type of
emission
 Mass of 4
 Charge of +2

Beta Decay
A - particle is emitted (a high energy electron)
0
−1
131
53
I
- or
131

54
0
−1
e
Xe
+
0
−1
e
Wait a tic

How does a nucleus
give off an electron!

Neutron splits into a
proton and electron.
n → p + + e-

Proton stays behind
and electron shoots
out of nucleus.
Positron Emission
A positron is emitted (a particle that has
the same mass as but opposite charge
than an electron)
0
+1
11
6
C
e
11

5
B
0
+ +1
e

Positrons are a
type of
“antimatter”.

Quickly destroyed
as soon as they
come in contact
with an electron.
Gamma Emission
High-energy radiation that almost always
accompanies the loss of a nuclear particle.
 It is NOT a particle, it is pure energy.
 No mass or charge.
 Not affected by a magnetic field.


0
0
Electron Capture
An electron close to
nucleus get “captured’.
It combines with a
proton to make a neutron.
1
1
p
+
0
−1
e

1
0
n
Penetrating Power

Penetrating Power:
how far radiation can
travel through
material.

Protection requires
different degrees of
shielding.
Alpha – paper or skin
Beta – aluminum foil
Gamma – thick lead
Ionizing Ability

Ionizing Ability: how well
radiation strips electrons
from other atoms and
molecules creating ions.

Can cause mutations, and cell
destruction

Alpha - Highest
Beta - Middle
Gamma – Low


Damage to Cells

Because of high ionizing
ability, Alpha and Beta
cause most damage
inside the human body.

Gamma rays are less
ionizing but protection
against gammas
requires thicker
shielding.
Measuring Radioactivity

One can use a device like a Geiger counter to
measure the amount of activity present in a
radioactive sample.
Natural Transmutation (Decay)
Spontaneous transmutation of a radioisotope
into another element.
 Doesn’t require the input of outside energy.
 Occurs at a specific rate that we can
measure. (Half Life)

Radioactive Series

Decay Series: very large
radioactive nuclei
undergo a “series” of
decays until they form a
stable nuclide (often a
nuclide of lead).
Artificial Transmutation

The change of one element to another artificially
by bombarding it with other particles.

These equations always have 2 reactants on the
left (as opposed to natural decay)
Artificial Transmutation
Natural Transmutation
How do We Bombard Nuclei?
Particle Accelerators:
Speed up charged particles
in a magnetic field to collide
with nuclei
Neutrons and gamma radiation
can’t be accelerated as they
have no charge!

Transuranium Elements:

Elements “beyond” uranium (largest natural element)
Atomic numbers greater than 92

Artificially created through nuclear bombardment

Video: Islands of Stability (13 minutes)
http://www.youtube.com/watch?v=woPx-Ex7H8A&safe=active
Typical Particle Accelerator
Enormous, with circular tracks with radii that
are miles long.
Brookhaven Accelerator
Balancing Nuclear Equations

Mass and charge
are “conserved”

Balance so that the
mass (top #’s) and
charge (bottom #’s)
equal each other.
Typical Test Questions
Half Life

Amount of time for half a radioactive sample to
decay.

Length of a half life cannot be changed.

Ranges from milliseconds to billions of years.
(See Table N)

Radioactivity decreases with time.
Radioactive Dating

Rate of decay is constant
over time.

Measure amount of
radioisotope remaining in
sample to determine age.

C-14 is used to date
organic material up to
60,000 years old.

U-238 is used to date
extremely old geological
formations

Carbon 14 Dating:n (2 minutes)
http://www.youtube.com/watch?v=31-P9pcPStg&safe=active

Reference Table N

Decay mode: type of
particle emitted by natural
decay

Half Life: length of time
for “half” of the atoms in a
sample to undergo natural
decay.
Half Life Formula:
# Half Lives = Total Time Elapsed
Time of One Half Life (t1/2 )
Half Life Problem

Ex:
If 500 grams of I-131, t1/2 = 8 days,
decays for 32 days, how much
would remain?

32 days = 4 half lives
8 days
500 g → 250 g→ 125 g → 62.5 g→ 31.25 grams
Half Life Problem

Ex:
If 300g of a radioisotope decays to
37.5g in 120 days, what is the t1/2 ?
300 → 150 → 75 → 37.5g
 3 half lives


3 half lives = 120 days
t1/2
t1/2 = 40 days
Half Life Problem


Ex:
What fraction of a sample of I-131
remains after 24 days of decay?
t1/2 = 8 days
24 days = 3 half lives
8 days
Start
End
1 → ½ → ¼ → 1/8
Half Life Problem

Ex:
If 60 g of N-16 remains in a
sample. How many grams were
present 28 seconds ago?
t1/2 = 7 sec.

28 sec = 4 half lives AGO
7 sec
We double going back in time
60 → 120 → 240 → 480 → 960 grams

After 32 days, 5 milligrams of an 80milligram sample of a radioactive isotope
remains unchanged.

What is the half-life of this element?
(1) 8 days
(2) 2 days
(3) 16 days
(4) 4 days
An original sample of K-40 has a mass of
25.00 grams. After 3.9 × 109years, 3.125
grams of the original sample remains
unchanged.
 What is the half-life of K-40?

(1) 1.3 × 109 y
(2) 2.6 × 109 y
(3) 3.9 × 109 y
(4) 1.2 × 1010 y

What is the half-life of sodium-25 if 1.00
gram of a 16.00-gram sample of sodium25 remains unchanged after 237 seconds?
(1) 47.4 s
(2) 79.0 s
(3) 59.3 s
(4) 118 s

How many days are required for 200.
grams of radon-222 to decay to 50.0
grams?
(1) 1.91 days
(2) 3.82 days
(3) 7.64 days
(4) 11.5 days
Honors Half Life Equations
Radioisotopes each have a unique half-life.
 Each will decay at a specific “rate” over time.
 Use the rate constant “k” to denote a specific
rate constant for an isotope in half-life
problems.

k = .693
t1/2
log N0 = k x t
N
2.3
N0 = original quantity
N = final quanity
t = total time
k = decay constant (.693)
t1/2
Half Life
Graph
http://www.absorblearning.
com/media/attachment.acti
on?quick=185&att=3167
Use the graph to see
how much time it takes
for half the nuclei to
decay
Energy in Nuclear Reactions

Nuclear reactions yield more
energy than chemical reactions

When changes happen to the
nucleus, some matter is
converted to energy.

Einstein’s famous equation,
E = mc2, allows us to calculate
this energy.
Energy in Nuclear Reactions
E = energy in Joules
 m = mass (lost) in kilograms
 c = the speed of light (3 x 108 meters/sec)

Energy in Nuclear Reactions
Ex:
The mass change for the decay of
1 mole of uranium-238 is 0.0046 g.
The change in energy, E, is then
E = (m) c2
E
= (4.6  10−6 kg)(3.00  108 m/s)2
E
= 4.1  1011 Joules
Mass Defect (Honors)

The difference between
the mass of an atom and
the sum of the masses of
the individual protons
and neutrons in it’s
nucleus.

The "vanishing" mass of
the protons and neutrons
is converted to energy.
Nuclear Fission
= Splitting the
Nucleus
Nuclear Fission



Large nuclei are split (basically in half), making
various “fission products” & large amounts of energy.
Mass after splitting is less than you started with.
Matter is converted to energy.
Recognize this Reaction
http://www.youtube.com/watch?v=T5g85zIDcec&safe=active

Nuclear Chain Reaction:
 Bombard nuclide with a neutron.
 Nuclei split releasing more neutrons that
strike other nuclei, and so on and so on....
Critical Mass: minimum amount of fissionable
material present for the chain reaction to be sustained.
Controlled vs. Uncontrolled Fission

Controlled Chain Reaction: occurs in
nuclear reactors or power plants.


Some of the free neutrons are removed
Uncontrolled Chain Reaction: occurs in
nuclear bombs or “atomic bombs”.
Video Clip:
Uncontrolled Fission
http://www.youtube.com/watch?v=DmSC_Or5y3Q&safe=active
Nuclear Power Plants
Nuclear Reactor
Generates heat through controlled nuclear
fission to produce steam that turns a turbine
connected to an electric generator.
Major Parts of a Nuclear Reactor

Fuel Rods:
 Contain a fissionable isotope
 Surrounded by coolant in reactor core
 Enriched U-235, Pu-239

Moderator:
 Slows down neutrons to increase
chances for fission.
 Graphite, water, or heavy water

Control Rods:
 Absorb excess neutrons
 Control rate of chain reaction
 Can be raised and lowered
 Boron or Cadmium
Neutron
Moderation and Absorption

Coolant:


Stops core from overheating
Transfers heat to heat exchanger


Shielding:


Steel reinforced concrete to protect workers from
radiation
Heat Exchanger:


Water, air, heavy water
Heat from fission is transferred to water which turns to
steam
Turbine:

Steam generates electricity
Bang Goes the Theory (3.5 min)
https://www.youtube.com/watch?v=MGj_aJz7cTs
Breeder Reactors
Use U-238, a nonfissionable but much
more plentiful isotope of uranium (99%).
 It undergoes transmutation into Pu-239 a
fissionable isotope of plutonium


Nuclear Power
supplies about
20% of the
country’s
electric power
Pros of Using Nuclear Power

What is positive about using nuclear
fission as a source of energy?

Large amount of energy from very small
quantity of fuel.

No greenhouse gas is produced (CO2)

Less reliance on foreign countries for fuel.
Cons of Using Nuclear Power

What are some of the negative aspects of
using nuclear fission as a source of
energy?
Exposure to
Radiation
Effects of Radiation Exposure
Somatic Effects:
Kills body cells or makes them cancerous.
 “Radiation sickness” (hair falls out, nausea,
fatigue, radiation “burns”)

Genetic Effects:

Mutations in eggs and sperm increase chance
of mutations in next generation.
IMPORTANT
Chemical properties of radioisotopes are the
same as nonradioactive. Form bonds the same way.
Why?
They have the same electron configurations and
valence shells.
Can get incorporated into bone, tissue, organs for a long time,
eventually causing mutations and cancer.
Ex: Sr-90 is chemically similar to Calcium
Ex: Radium Girls: Watch Dial Painters (5 minutes)
https://www.youtube.com/watch?v=p51S8_zWO2s
The story of Radium (10 minutes) https://www.youtube.com/watch?v=wAZX8sWSCqs
Long-term
Storage of
Radioactive
Wastes
(JUST READ)
 Since the 1940s, the United States has
generated over 75,000 metric tons of spent
nuclear fuel and high-level nuclear waste at 80
sites in 35 states.

That’s enough to fill
a football field about
15 feet deep.

Nuclear waste is expected to increase by about
2,000 metric tons per year, more than doubling
to 153,000 metric tons by 2055.
The closest we’ve come to
a long term nuclear-waste
storage has been Yucca
Mountain: a “geological
repository,” site about 100
miles Northwest of Las
Vegas.
Nuclear Reactor
Malfunctions
Three Mile Island,
PA (1979)
Worst accident in
U.S. nuclear power
plant history.
 Released moderate
amounts of
radioactive gases
into the
environment

Chernobyl,
Ukraine
(1986)
Video:
http://youtu.be/BfKm0XXfiis
Chernobyl: 11 min PBS
https://www.youtube.com/watch?v=Kbcb
yUK5rqQ
Fukashima,
Japan (2011)
Fukashima revisted:
https://www.youtube.com/watch?v=jsr-CTGhzak
“Nuclear Boy Cartoon”
https://www.youtube.com/watc
h?v=45gxTXgvK50&safety_m
ode=true&persist_safety_mod
e=1&safe=active
Bang Goes the Theory (2 min)
https://www.youtube.com/watc
h?v=rySfb7OUFXc
Nuclear Fusion =
Joining Nuclei Together
Nuclear Fusion

Nuclear Fusion: the joining together of
smaller nuclei to make larger ones.
Recognize this Type of Equation
Fission Vs. Fusion
It’s Really Hard to do!

Due to the repulsive forces between
positive nuclei, this requires extremely
high temp. and pressures.
Stars = Fusion Reactors

Stars generate
energy through
fusion.

All elements in the
universe were formed
through the process
of fusion.
Video: How elements are formed 5 minutes
https://youtu.be/neMEo8ZrwuI
Nuclear Fusion
Pros
 Produces more energy than fission.
 Fuel (hydrogen) is plentiful
 No radioactive waste
Cons
 High temp./pressure needed to initiate.
 Material must be in the plasma state
at several million Kelvin.
 No fusion reactors exist, still in
research stage.
Nuclear Frusion 7:55 min
https://www.youtube.com/watch?v=N4yWhA1mVxA&feature=em-share_video_user
Nuclear Fusion Reactor?




Tokamak apparati like the
one shown at the right
show promise for carrying
out these reactions.
They use magnetic fields
to heat the material.
Recent Headline
http://www.dailymail.co.uk/sciencetech/article3429515/Scientists-inject-fuel-experimental-fusiondevice.html
Hydrogen “Fusion” Bomb
Thermonuclear
Bomb:
A fission bomb
explodes, providing
the heat and
pressure necessary
for fusion to occur.
Much more
destructive than an
atomic “fission”
bomb
Otherwise known as “Dabomb”
Crash Course Chemistry








Bill Nye: Nuclear Energy (25 minutes)
https://www.youtube.com/watch?v=aDdPk0-SDmI
Nuclear Chem Part 1
http://www.youtube.com/watch?v=KWAsz59F8gA&safe=active
Fission and Fusion
http://www.youtube.com/watch?v=FU6y1XIADdg&safe=active
Chernobyl: 11 min PBS
https://www.youtube.com/watch?v=KbcbyUK5rqQ
Uses of Radiation
https://www.youtube.com/watch?v=E4B94zCY4ok
Dating Materials

Half Lives don’t change!

Carbon-14: date organic materials

Uranium-238: date extremely old
geological formations (very long half life)
Non-Invasive Body Imaging
Radioactive
material injected
Radiation detected
to give image
Used to:
Locate tumors
Determine organ
function
Skeletal Scan
of Person After
a Tc-99m
Injection
Cancer Treatment

Direct external radiation beam at tumor,
usually from Co-60 gamma radiation.
Or

Internally deposit “seeds” containing
radioactive materials near tumor site.
Therapy
Machine used
for Targeting
Cancerous
Tissue
Important!!!

Isotopes used in medical diagnosis and
treatment should always have:
SHORT HALF LIVES
BE QUICKLY ELIMINATED FROM THE BODY
Some Isotopes Used in Medicine
Important.

I-131: treat and diagnosis thyroid disorders

Co-60: emits gamma radiation to treat cancer

Tc-99: treats brain tumors

Th-201: useful to study damage to the heart
Tracers:

Radioisotopes react chemically the same way as
nonradioactive (same # valence electrons).

Use them to “trace” the path of a chemical through
the body or through a chemical reaction mechanism.

Ex: C-14, P-32, O-18
Sterilization:
Gamma rays kill bacteria, mold, fungus on surface.

Medical instruments

Food (ground beef, strawberries, etc.)
 gives
food a longer shelf-life
 prevents E-coli outbreaks
 Controls sprouting
 Does not make the food radioactive
 FDA Approved
Spacecraft Power Supplies

Have allowed space craft to explore the
outer solar system, too far from the sun for
solar panels to be effective

The End