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