Isotopes & Radioactive Decay

Electromagnetic Spectrum Radiation High energy rays and particles emitted by radioactive sources. (most invisible to human eyes) Includes: electromagnetic spectrum, alpha & beta particles. Electromagnetic Spectrum Radioactivity – release of high energy particles and rays of energy from substance as a result of changes in the nuclei of its atom Use radioactivity for medical diagnoses by generating electricity Light is form of radiation visible to us Radio waves – TV, cell phones, radio, etc, Infrared – warm objects – human body, ovens, curling iron, stovetop, remote controls, UV – the sun & black lamp, XRAY –cat scan (dentists and hospitals, airports), gamma rays – cancer treatments

Radioactivity The release of high-energy particles and rays from a substance due to changes in the nuclei of its atoms. Naturally occurring radiation found in our environment is called: “Natural Background Radiation” Natural background radiation – stream of high energy & fast moving particles found in environment Roentgen discovered energy emitted from materials when he bombarded them w/ electrons  unknown rays “X” rays French physicist Becquerel – discovered that uranium salts emitted rays that darkened photographic plates – caused photographs to be exposed Radioactive material (Iron-59) releases energy which is detected by equipment to make images of body parts Radioactivity can be useful, such as in medical diagnoses and treatment (X-rays, Chemotherapy, etc.) and in generating electricity (Nuclear power plants)

Isotopes Atoms of the same element that have the… Same number of protons (same atomic number) Different number of neutrons Since the number of neutrons differs, the mass number also differs. Mass number = protons + neutrons Different isotopes of the same element all have: The same chemical symbol The same atomic number (# of protons) Different mass numbers

Representing Isotopes Use standard atomic notation Symbol + Atomic number + Mass number Also called “Nuclear Symbol” X Mass # Atomic # e.g.: Potassium has 3 naturally occurring isotopes. 39 K 40 K 41 K 19 19 19 K = on periodic table potassium has mass of 39.1 – we will see why Mass # = superscript Atomic # = subscript Potassium-39 Potassium-40 Potassium-41 Protons 19 19 19 Neutrons 20 21 22 Electrons 19 19 19

Atomic Mass In nature, most elements are found as a mixture of isotopes. Potassium-39 Potassium-40 Potassium-41 93.26% 0.01% 6.73% Each banana has the same relative abundance of potassium isotopes The atomic mass of an element is the average of all the naturally occurring isotopes. Potassium has 25 known isotopes from K32 to K56 Those are the 3 naturally occurring isotopes 39 and 41 are stable Atomic mass = (.9326 x 39) + (.0001 x 40) + (.0673 x 41) = 39.1

Assignment Classwork: Homework: Practice Problems Q. 1-4 Page 291 “Isotopes” Worksheet Homework: “Isotopes and Ions” Worksheet