Transcript Nuclear Chemistry

Nuclear Chemistry
Chapter 25
What do you think of when you
hear Nuclear Chemistry?

Henri Becquerel (1852-1908)
◦ Originally thought sunlight caused uranium to
radiate
◦ Discovered the spontaneous radiation while
waiting for a sunny day to test his theory

Marie Curie (1867-1934) and her husband
Pierre Curie (1859-1906)
◦ Worked w/ Becquerel
◦ Eventually showed that the rays were from
uranium atoms
◦ Came up with the term “radioactivity” to
describe
History

Some isotopes are stable and others are
not.
◦ Nucleus is protons and neutrons
 Protons are positive so they repel
 Neutrons are only stable when near a proton
◦ Some have:
 Too many protons
 Too many neutrons
 Just plain too many
◦ So they “fall apart”
Why Radioactive?
First 3 kinds of radiation found
First 3 kinds of radiation found

ALPHA
◦ Positive matter
◦ Exactly like a Helium
nucleus

BETA
◦ Negative matter
◦ Exactly like an
electron

GAMMA
◦ High energy wave
◦ NOT matter so no
charge
Summary of Radiation

Alpha Radiation- when a helium nuclei has
been emitted from a radioactive source.
Types of Radiation

Beta Radiation – An electron resulting
from the breaking apart of a neutron in an
atom.
Types of Radiation
Gamma Radiation – a high-energy photon
emitted by a radioisotope.
(electromagnetic radiation)
 Extremely Dangerous!

Types of Radiation
Type of
Radiation
Symbol
Alpha
𝛼
Beta
𝛽
Gamma
𝛾
Mass
Nuclear
Charge
Particle
4 amu
2+
4
2𝐻𝑒
1-
𝑒−
0
𝛾
1
1840
amu
0

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
Look for patterns
Try to explain the patterns
Test your ideas with known things
Use the pattern to figure out unknown
things
Adjust as necessary!
How can we use what we know?
The blue ones have at least one stable isotope. Others do not!
http://catalog.flatworldknowledge.com

Chart helps predict type of decay
◦ Too many neutrons?
 Emit a beta particle to change a neutron to a
proton and move closer to the band of stability
◦ Just too big?
 Emit an alpha particle to reduce size of nucleus

There are many types of decay, but chart
helps give us targets when trying to
manipulate elements to do what we want
How does this help?
Mass numbers and charges are conserved
(equal on both sides)
 Example Alpha Decay

◦
◦
◦
◦
◦
◦
◦
238
94𝑃𝑢
→ 𝐴𝑍𝑋 + 42𝐻𝑒
Mass number of product A= ?
Atomic Number of product Z= ?
Reaction Product X = ?
238= A+4
94=Z+2
So… 234
92𝑈 is the answer
Writing and Balancing Nuclear
Equations


Mass numbers and charges are conserved
(equal on both sides)
Example Beta Decay
238
94𝑃𝑢
→ 𝐴𝑍𝑋 + 𝑒 − ( −10𝛽)
Mass number of product A= ?
Atomic Number of product Z= ?
Reaction Product X = ?
since beta decay is the break up of a neutron into a
proton and an electron the mass # doesn’t change
◦ Z will be one greater Z= 95
◦ So… 238
95𝐴𝑚 is the answer
◦
◦
◦
◦
◦
Writing and Balancing Nuclear
Equations

Show the products of Bismuth -212
undergoing an alpha decay
 212
83𝐵𝑖

→ 42𝐻𝑒 +
208
81𝑇𝑙
Now the Daughter thallium undergoes a
beta decay
 208
81𝑇𝑙
→ 𝑒 − ( −10𝛽) +
Practice
208
82𝑃𝑏

Half-Life is the time required for half of
the atoms in a radioactive sample to
decay
Number of
half-lives
Elapsed time
Amount of
strontium-90
present
0
0y
10.0g
1
29 y
5.00g
2
58 y
2.50g
3
87 y
1.25g
4
116 y
0.625g
Half -Life
Practice
 Bandages can be sterilized by exposure to
gamma radiation from colbalt-60, which
has a half-life of 5.27 years. How much of
a 10.0 mg sample of cobalt-60 is left after
one half-life? Two half-lives? Three halflives? How many years is 3 half-lives?
 5.00mg; 2.50mg; 1.25mg; 15.81y
Half-Life