CHAPTER 21 Nuclear chemistry Nuclear Decay Why nuclides

CHAPTER 21 Nuclear chemistry

Nuclear Decay ª Why nuclides decay… w need stable ratio of neutrons to protons

Types of Radiation ª Alpha particle ( ) w helium nucleus ª Beta particle ( -) w electron ª Positron ( +) w positron ª Gamma ( ) w high-energy photon 2+ 1 - paper lead 1+ 0 concrete

Half-life ª Half-life (t½) w Time required for half the atoms of a radioactive nuclide to decay. w Shorter half-life = less stable.

Half-life mf: final mass mi: initial mass n: # of half-lives

Half-life ª Fluorine-21 has a half-life of 5. 0 seconds. If you start with 25 g of fluorine-21, how many grams would remain after 60. 0 s? GIVEN: WORK: t½ = 5. 0 s mf = mi (½)n mi = 25 g mf = (25 g)(0. 5)12 mf = ? mf = 0. 0061 g total time = 60. 0 s n = 60. 0 s ÷ 5. 0 s =12 C. Johannesson

Nuclear Decay ª Alpha Emission parent nuclide daughter nuclide alpha particle Numbers must balance!!

Nuclear Decay ª Beta Emission ª Positron Emission electron positron

Nuclear Decay ª Electron Capture electron ª Gamma Emission w Usually follows other types of decay. ª Transmutation w One element becomes another.

A. Mass Defect ª Difference between the mass of an atom and the mass of its individual particles. 4. 00260 amu 4. 03298 amu

B. Nuclear Binding Energy ª Energy released when a nucleus is formed from nucleons. ª High binding energy = stable nucleus. E= 2 mc E: energy (J) m: mass defect (kg) c: speed of light (3. 00× 108 m/s)

B. Nuclear Binding Energy Unstable nuclides are radioactive and undergo radioactive decay.

II. Radioactive Decay