Nuclear Chemistry Chapter 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 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

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” Why Radioactive?

First 3 kinds of radiation found

First 3 kinds of radiation found

Summary of Radiation ALPHA BETA GAMMA 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 Gamma Radiation – a high-energy photon emitted by a radioisotope. (electromagnetic radiation) Extremely Dangerous! Types of Radiation

Type of Radiation Symbol Mass Nuclear Charge Particle Alpha  𝛼   4 amu  2 +   2 4 𝐻𝑒  Beta  𝛽   1 1840 amu  1 - 𝑒 −   Gamma   𝛾  0

How can we use what we know? 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

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 How does this help?

Writing and Balancing Nuclear Equations Mass numbers and charges are conserved (equal on both sides) Example Alpha Decay 94 238 𝑃𝑢 → 𝑍 𝐴 𝑋 + 2 4 𝐻𝑒 Mass number of product A= ? Atomic Number of product Z= ? Reaction Product X = ? 238= A+4 94=Z+2 So… 92 234 𝑈 is the answer Writing and Balancing Nuclear Equations

Writing and Balancing Nuclear Equations Mass numbers and charges are conserved (equal on both sides) Example Beta Decay 94 238 𝑃𝑢 → 𝑍 𝐴 𝑋 + 𝑒 − ( −1 0 𝛽 ) 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… 95 238 𝐴𝑚 is the answer Writing and Balancing Nuclear Equations

Practice Show the products of Bismuth -212 undergoing an alpha decay 83 212 𝐵𝑖 → 2 4 𝐻𝑒 + 81 208 𝑇𝑙 Now the Daughter thallium undergoes a beta decay 81 208 𝑇𝑙 → 𝑒 − ( −1 0 𝛽 )+ 82 208 𝑃𝑏 Practice

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 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

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 half- lives? How many years is 3 half-lives? 5.00mg; 2.50mg; 1.25mg; 15.81y Half-Life