UNIT 13: NUCLEAR CHEMISTRY
REVIEW: ISOTOPE NOTATION
A
An isotope notation is written as ZX, where X is the element, A is the
mass number (sum of protons and neutrons), and Z is the atomic
number.
For example…
238
92U
U is for uranium, mass number is 238, and atomic number is 92
The isotope can also be written as uranium-238 for short since
uranium will always have the atomic number of 92.
WHAT IS NUCLEAR CHEMISTRY?
Nuclear chemistry is the study of processes in which the
nuclei of various atoms change in some way.
Three different types of changes:
•Radioactive decay
•Nuclear fission
•Nuclear fusion
RADIOACTIVE DECAY
Radioactive decay is when an unstable nucleus breaks apart
into smaller nuclei, or changes in some other way to make it
more stable.
All elements have radioactive isotopes in which the ratio of
protons to neutrons makes the nuclei unstable.
•All elements past uranium have NO stable isotopes. As a result, all
of these elements undergo radioactive decay of some sort.
NUCLEAR RADIATION
When radioactive decay occurs, the nuclei of an element
either gain or lose pieces in order to gain a more stable
ratio of protons to neutrons. Here are the following types
of nuclear decay you need to know:
•Alpha radiation (α)
•Beta radiation (β)
•Gamma radiation (γ)
ALPHA RADIATION
•Alpha particle is a helium nucleus with 2 protons and 2
neutrons. It has a +2 charge.
•Alpha particle can be written as 24α or 24He
•Alpha particles are the largest type of radiation particle
and most highly charged.
•Alpha particles can be blocked by your hand, clothes, or a
sheet of paper.
ALPHA DECAY
•This is when a nucleus loses an alpha particle (a helium
nucleus) to become more stable.
•One example of this reaction is the alpha decay of U-238
238
92U →
4
2He
+
234
90Th
EXAMPLE:
polonium-210
thorium-230
BETA RADIATION
•Beta particle is an electron. It has a -1 charge.
•Beta particle can be written as
0
β
or
−1e.
−1
0
•Beta particles are fast-moving and can have high energy.
•Alpha particles can be blocked by thin metal foil.
BETA DECAY
•This is when there is an uneven ratio of neutrons to protons in
the nucleus (too many neutrons), an excess neutron will split.
•One example of this reaction is the beta decay of Lead-210
210
82Pb →
0
−1e
+
210
83Bi
EXAMPLE:
carbon-14
thorium-231
GAMMA RADIATION
•Gamma ray is high-energy photon or ray. It has a no charge.
•Gamma ray can be written as 00γ
•Gamma rays are high frequency and the most penetrating
type of radiation. This makes them the most harmful to
human.
•Alpha particles can be blocked by thick lead shield or
concrete block.
GAMMA EMISSION
•This is when the nucleus needs to get rid of excess energy and
achieve stability during nuclear reaction.
•Usually gets emitted along with alpha and beta particles.
•One example of this reaction is the beta decay of Cobalt-60
60
27Co →
60
28Ni
+ −10e + 2 00γ
Cobalt-60 decay by beta emission to excited Nickel-60. Then
excited 60Ni falls to stable ground state of 60Ni by emission of
2 gamma rays
EXAMPLE:
carbon-11
oxygen-15
HOW TO WRITE A BALANCED NUCLEAR EQUATION
•Step 1: Write the full symbol of the nuclide that’s
decaying.
•Step 2: One of the products of this reaction is the nuclear
radiation particle (alpha, beta, or gamma).
•Step 3: Figure out the other product. Because the law of
conservation of mass does a pretty good job of describing
how the world works, the mass of the particle and the
atomic number will add up to be the same as the reactant
side
DECAY SUMMARY
Type of Radioactive Particle
Decay
Emitted
Change in Mass Change in
Number
Atomic Number
Alpha Decay
α
Decreases by 4
Decreases by 2
Beta Decay
β
No Change
Increases by 1
Gamma Decay
γ
No Change
No Change
BALANCED NUCLEAR EQUATION EXAMPLE
Complete each of the following nuclear equation
1.
226
88Ra
2.
38
19K
→ 42He + ______________
→ ____________ + −10β
3. ____________ + 10n →
15
1
N
+
7
1H
MORE EXAMPLE…
Complete each of the following nuclear equation
1.
69
30Zn
2.
208
84Po
→
69
31Ga
→
233
3. 92U
+ ______________
204
82Pb +
1
______________
+ 0n →
92
44Ru
1
+ 3 0n + ______________
REMINDER!!!
Quiz tomorrow…use the quiz
review to help study
Unit 13 test on Tuesday!
NUCLEAR FISSION
Nuclear fission occurs when
large, unstable atoms
(usually isotopes of
uranium and plutonium) are
split by a neutron into
smaller, more stable atoms.
During this process, huge
amounts of energy are
generated.
HOW DOES NUCLEAR FISSION WORK?
•Fission happens when the nuclei are bombarded by
neutrons.
•The large nuclei split into two or more smaller nuclei,
releasing neutrons, and a large amount of energy.
•A chain reaction can be created, and a tremendous
amount of energy can be release in a very short amount
of time.
HOW DOES NUCLEAR FISSION WORK?
NUCLEAR FISSION IN REAL LIFE
Nuclear power plants are powered by fission reaction.
Since a very large amount of energy can be released in a
very short amount of time, fission must be controlled!
A control rod is inserted into the reaction in order to
absorb neutrons, and help keep the chain reaction from
multiplying.
NUCLEAR FUSION
Nuclear fusion is the
opposite of fission. Nuclear
fusion occurs when smaller
atoms fuse together to form
larger, more stable atoms.
This type of reaction
releases even more energy
than a fission bomb.
NUCLEAR FUSION IN REAL LIFE
•Fusion is hard to use in practical applications because it
requires very high temperatures (108K).
•Such extreme temperatures exist, however, in stars, and
fusion is responsible for the energy released by the sun.
WHERE DOES THE ENERGY COME FROM?
The energy released from fission and fusion comes
from the nuclear binding energy.
Law of conservation of energy and law of
conservation of mass… when the larger nuclei split
up into smaller nuclei, some mass is loss. To make up
for that loss, the energy is released.
HALF-LIFE
•Half-life: is the amount of time it takes for one-half of a
radioisotope sample to decay into its products.
•During one half-life, half of the original sample will decay.
•The shorter the half-life time, the less stable the isotope is
going to be.
EXAMPLE:
The half-life of the radioisotope strontium-90 is 29 years.
If you had 10 grams of strontium-90 today, how much
would you have 29 years from now?
How much would be left in 58 years?