Nuclear ChemistryChapter 25
What do you think of when you hear Nuclear Chemistry?
History
Henri Becquerel (1852-1908) ◦Originally thought sunlight caused uranium to
radiate◦Discovered the spontaneous radiation while
waiting for a sunny day to test his theoryMarie 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
Why Radioactive?
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”
First 3 kinds of radiation found
First 3 kinds of radiation found
Summary of Radiation
ALPHA◦Positive matter◦Exactly like a Helium
nucleusBETA
◦Negative matter◦Exactly like an
electronGAMMA
◦High energy wave◦NOT matter so no
charge
Types 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!
Type of Radiation Symbol Mass Nuclear
Charge Particle
Alpha 4 amu 2 +
Beta amu 1 -
Gamma 0 0
How can we use what we know?
Look for patternsTry to explain the patternsTest your ideas with known thingsUse the pattern to figure out unknown
thingsAdjust as necessary!
The blue ones have at least one stable isotope. Others do not!
http://catalog.flatworldknowledge.com
How does this help?
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
Writing and Balancing Nuclear Equations
Mass numbers and charges are conserved (equal on both sides)
Example Alpha Decay
◦Mass number of product A= ?◦Atomic Number of product Z= ?◦Reaction Product X = ?◦ 238= A+4◦94=Z+2◦So… is the answer
Writing and Balancing Nuclear Equations
Mass numbers and charges are conserved (equal on both sides)
Example Beta Decay
◦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… is the answer
Practice
Show the products of Bismuth -212 undergoing an alpha decay
Now the Daughter thallium undergoes a beta decay
Half -Life
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 0 y 10.0g
1 29 y 5.00g
2 58 y 2.50g
3 87 y 1.25g
4 116 y 0.625g
Half-Life
PracticeBandages 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 half-lives? How many years is 3 half-lives?
5.00mg; 2.50mg; 1.25mg; 15.81y
