Nuclear Chemistry Nuclear Chemistry

Facts About the Nucleus Very small volume compared to volume of atom Essentially entire mass of atom Very dense Composed of protons and neutrons that are tightly held together called Nucleons 2

Facts About the Nucleus (cont.) The number of neutrons is calculated by subtracting the atomic number from the mass number. The nucleus of an isotope is called a nuclide. Less than 10% of the known nuclides are nonradioactive. Most are radionuclides. 3

Electromagnetic Spectrum

Radioactivity Henri Becquerel (1896) Accidentally placed a uranium sample on some unexposed photographic film, which caused it to be “developed” Uranium – one of the naturally radioactive elements http://www.if.ufrj.br

During radioactive decay, atoms of one element are changed into atoms of a different element. In order for one element to change into another, the number of protons in the nucleus must change All nuclides with 84 or more protons are radioactive We describe nuclear changes using nuclear equations. Atomic numbers and mass numbers are conserved

Marie Curie One of the first female scientist allowed to work in a lab, but only b/c she worked with her husband Pierre (who was later killed by a horse & buggy). She was then granted permission from the University to continue to work by her self. Discovered 2 elements: Radium & Polonium (she named it for her motherland Poland). Only person to win a Nobel Prizes in 2 different categories; Physics (1903) and Chemistry (1911) Kept radioactive materials in her pocket Died of leukemia from radioactive materials Her work & body are at a museum dedicated to her in Poland. Which are kept under lead because they are still radioactive today! Total time of video 2: 56

 Alpha Decay  An  particle contains 2 protons and 2 neutrons. = Helium nucleus Loss of an alpha particle means Atomic number decreases by 2 Mass number decreases by 4 5

 Beta Decay  A  particle is like an high-speed electron Moving much faster Found in the nucleus When an atom loses a  particle its: Atomic number increases by 1 Mass number remains the same In beta decay a neutron changes into a proton:

 Gamma Emission  Gamma () rays are high energy photons Gamma emission occurs when the nucleus rearranges No loss of particles from the nucleus No change in the composition of the nucleus (same atomic number and mass number) Generally occurs whenever the nucleus undergoes some other type of decay 6

Penetrating Power

Radioisotopes radioactive isotope half – life many elements have at least 1 radioactive isotope half – life the time it takes for ½ of a sample of an isotope to decay

The longer the half-life the more slowly the rate of decay The longer the half-life the more slowly the rate of decay. The slower the decay the less ,  and  radiation is emitted.

Uses for half-life? Determine the age of substance Determine how much of a substance will be left Ex: Carbon-dating Half–life of carbon – 14 is 5730 years

Half - Life Ex: half-life of rubidium–87 is 6 X 10 10 years (60 billion) It takes 60 billion years for half of the sample to decay. If I started out with 100 g how many grams would be left after 60 billion years? Rb–87  Sr–87 What type of decay?

Half-life Problems To solve you are going to need to know some information such as: Half-life Time Initial Mass Final Mass Number of half-lives Total Time If you are given some of these you can solve for the others

Example 1 Or you can do it the “mathy way” Half-life of an isotope of plutonium is 140 days The original sample contained 10.0 grams How much is left after 420 days? Step 1- find the number of ½ lives = (total time/ ½ life time) Step 2- find the final mass “loopy way” Or you can do it the “mathy way” Final mass = (initial mass divide by 2 #halflives)

Example 2 Three grams of Bismuth-218 decay to 0.375 grams in one hour. What is the half-life of this isotope?

Example 3 Half life of cesium – 137 is 30.2 years Initial mass is 1.00 kg How much will remain after 151 years?

Example 4 A 2.5 gram sample of an isotope of strontium-90 was formed in a 1960 explosion of an atomic bomb at Johnson Island in the Pacific Test Site. The half-life of strontium-90 is 28 years. In what year will only 0.625 grams of this strontium-90 remain?

Example 5 The half-life of carbon-14 is 5730 years. How old is a fossil that once contained 100. g of C-14 and it now contains 0.78125g?

Beneficial Uses of Radioisotopes Food Preservation- kills microorganisms – molds and bacteria Radiotracers- radioactive labels – used to follow a specific substance through a natural system Iodine – 131, used to see Thyroid Issues Barium sulfate, used to detect Gastrointestinal problems

Cancer treatment cancer cells are more sensitive to radiation Teletherapy – narrow beam of high – intensity gamma radiation used to destroy tumors Radioactive “seeds” – implanted in tumors – emit beta and gamma radiation and kill surrounding cancer cells Chemotherapy is not radiation since it uses chemicals to destroy cancer cells