Chemistry Unit 4 Chapter 25 Nuclear Chemistry Mass Defect Difference between the mass of an atom and the mass of its individual particles. amu amu Nuclear Binding Energy
Energy released when a nucleus is formed from nucleons. High binding energy = stable nucleus. E = mc2 E:energy (J) m:mass defect (kg) c:speed of light (3.00108 m/s) Nuclear Binding Energy
Unstable nuclides are radioactive and undergo radioactive decay. Types of Radiation 2+ 1- 1+ Alpha particle () Beta particle (-)
helium nucleus paper 2+ Beta particle (-) electron 1- lead Positron (+) positron 1+ concrete Gamma () high-energy photon Nuclear Decay Numbers must balance!! Alpha Emission parent nuclide
daughter nuclide alpha particle Numbers must balance!! Nuclear Decay Beta Emission electron Positron Emission positron Nuclear Decay Electron Capture electron Gamma Emission Transmutation
Usually follows other types of decay. Transmutation One element becomes another. IQ# 1 Balance the following equations: Nuclear Decay Why nuclides decay
need stable ratio of neutrons to protons Band of Stability and Radioactive Decay Half-life Half-life (t)
Time required for half the atoms of a radioactive nuclide to decay. Shorter half-life = less stable. Half-life mf:final mass mi:initial mass n:# of half-lives Half-life t = 5.0 s mi = 25 g mf = ? total time = 60.0 s
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: t = 5.0 s mi = 25 g mf = ? total time = 60.0 s n = 60.0s 5.0s =12 WORK: mf = mi ()n mf = (25 g)(0.5)12 mf = g Fraction left after 5 half-lives = 500g (0.5)5 Mi = 500 g n = 5 Mf = ?
Example: How much of a 500. g sample of Uranium-235 would be left after five half-lives? Example:A mg sample of Radon-222 decays to mg after 24 hours.Determine the half-life. Fraction left after 5 half-lives = 500g (0.5)5 Mi = 500 g n = 5 (n = # of half-lives) Mf = ? Mf = g 16 8 42 1 0.5 0.25 = 6 half lives Example: The half-life of molybdenum-99 is 67 hours. How much of a 1
Example: The half-life of molybdenum-99 is 67 hours.How much of a mg sample is left after 335 hours? Mi = mg Half-life = 67 h Rxn time = 335 h Mf = ? n = 335 / 67 = 5 Mf = mg Learning Check! The half life of I-123 is 13 hr.How much of a 64 mg sample of I-123 is left after 39 hours? Half Life and Radioactivity Lab
Work in groups of 2 at your table. Each cup has 1 penny in it which will be shaken and then GENTLY emptied on the table. For the first trial, shake the penny out 100 times on the table. Record the number of times that it came up heads. For the next trail, you will shake out the penny the number of times that it landed on heads in the last round. The same procedure will follow until no more of the pennies have landed on heads (tails = decayed). Record all data in the lab book following the example on page 809. Answer questions 1-4 and be sure to follow the graphing rules (R74 and in the Math Review handout from the beginning of the year). Graphing the Results Important !! Graph directly on lab book
Title every graph and label each axis Graph at least 2/3 page Use a ruler Circle all data points Use a best-fit line (no connect the dots!) 5) Find the average half-life (in # of trials) of your sample by interpolating your curve at exactly 50, 25, and 12.5 flips) F ission splitting a nucleus into two or more smaller nuclei
1 g of 235U =3 tons ofcoal F ission chain reaction - self-propagating reaction
critical mass -mass requiredto sustain achain reaction Fusion combining of two nuclei to form one nucleus of larger mass
thermonuclear reaction requires temp of 40,000,000 K to sustain 1 g of fusion fuel =20 tons of coal occurs naturally instars Fission vs. Fusion 235U is limited danger of meltdown toxic waste
thermal pollution fuel is abundant no danger of meltdown no toxic waste not yet sustainable Nuclear Power Cooling Tower Fission Reactors Nuclear Power Fission Reactors Nuclear Power Fusion Reactors (not yet sustainable) Nuclear Power Fusion Reactors (not yet sustainable)
National Spherical Torus Experiment Tokamak Fusion Test Reactor Princeton University Synthetic Elements Transuranium Elements
elements with atomic #s above 92 synthetically produced in nuclear reactors and accelerators most decay very rapidly Radioactive Dating half-life measurements of radioactive elements are used to determine the age of an object decay rate indicates amount of radioactive material EX: 14C - up to 40,000 years 238U and 40K - over 300,000 years Radiation treatment using
Nuclear Medicine Radioisotope Tracers absorbed by specific organs and used to diagnose diseases Radiation Treatment larger doses are usedto kill cancerous cellsin targeted organs internal or externalradiation source Radiation treatment using -rays from cobalt-60. Nuclear Weapons Atomic Bomb Hydrogen Bomb
chemical explosion is used to form a critical mass of 235U or 239Pu fission develops into an uncontrolled chain reaction Hydrogen Bomb chemical explosion fission fusion fusion increases the fission rate more powerful than the atomic bomb Others Food Irradiation Radioactive Tracers Consumer Products
radiation is used to kill bacteria Radioactive Tracers explore chemical pathways trace water flow study plant growth, photosynthesis Consumer Products ionizing smoke detectors - 241Am