Chapter 11 Nuclear Chemistry

1. Chapter 11 Nuclear Chemistry

2. Radioactive Elements • Radioactivity – release of energy and matter from changes in an atom’s nucleus • Some elements or some of their isotopes (atoms w/ different mass #’s) are radioactive • A new way to write an atomic symbol: mass numberAtomic Symbol atomicnumber 12C 6 Try Sodium on your own….

3. II. Transmutation of Elements • Transmutation or Radioactive Decay – change of one element to another (e.g., U changing to Pb) • Decay Series– series of steps by which a radioactive nucleus changes to a nonradioactive one (Fig 11-6) • Alpha Decay – when a nucleus releases 2 protons and 2 neutrons together ( a He nucleus) • Beta Decay – when a nucleus releases an electron… • “But wait Mrs. O’Gorman, you told us that electrons are not in the nucleus…” • Well, scientists believe that a neutron is nothing but a proton and an electron that are hooked up and disguised as a neutral charge…

4. III. Transmutation of Elements (Cont’d) • Gamma Decay – release of energy in the form of gamma rays that accompanies α (alpha) and β (beta) decay Decay or die! (try these) • Illustrate the alpha decay of Polonium – 216 • Illustrate the beta decay of Bismuth – 210

5. III. Transmutation of Elements (Cont’d) • To sum up, the “rules” of radioactive decay are: • Alpha Decay – nucleus loses 2 P’s and 2 N’s • Beta Decay – nucleus loses an electron (the electron was produced by the breakdown of a neutron) • Gamma Decay – accompanies Alpha and Beta Decays – nucleus releases a HIGH energy wave called a Gamma ray

6. II. Transmutation of Elements • Half-life – amount of time it takes half the atoms in a sampleof radioactive material to decayinto a stable, non-radioactive element (Fig. 11-12) • Half-life of Polonium-215 is 0.0018 second • Half-life of Uranium-218 is 4.5 billion years!! • Suppose you have 100 grams of Po-215… • How much Po is left after 0.0018 seconds? • After 0.0036 sec? • After 0.0072 sec? • Suppose you are given 600 g of U-238… • How large was the sample 2.25 billion years ago? • In how many years would I expect to see ONLY 300 g of U-238 left in my sample? • How much, and what decay material, would I have along with my 300 g of U-238 (see your textbook) ?

7. III. Transmutation of Elements • Nuclear Fission • Splitting of a large atom into two smaller ones by a neutron bullet • Releases energy • Can be controlled so it’s used for nuclear power • INDIAN POINT = FISSION • 235 U + 1 n 92 Kr + 141 Ba + 3 1 n 920 36 56 0 • Nuclear Fusion • fusing of two smaller atoms to form a larger one • TREMENDOUS Release of energy • Difficult to control so we don’t use it as an energy source • This is how the SUN produces so much heat and radiation energy • FUSION = SUN

8. IV. Detecting & Measure Radioactivity • Electroscope (Fig. 11-17) • Separated foil leaves collapse if a radiation source is near • Geiger Counter (Fig. 11-18) • Makes a click every time a radiation particle hits it • # of clicks per unit time indicates the radiation strength • Cloud chamber (Fig. 11-19) • Radiation particles leave visible trails through alcohol vapor • Bubble chamber (Fig. 11-20) • Similar to a cloud chamber

9. V. Uses of Radioactivity • Radioisotopes – artificially produced radioactive isotopes of common elements • Used as tracers whose paths can be followed with instruments • Iodine-131 collects in the thyroid gland so doctors can observe any problems that a person my be having with their thyroid. • Iron-59 collects in blood • Some food is “irradiated” to kill bacteria so it will stay safe to eat for long periods of

10. Practice of Half-Life Calculations • Fill in this chart of the half-life decay of Carbon-14 Half Life #Time ElapsedAm’t of C14 Remaining 0 0 1600g 1 5730 800g 2 11460 400g 3 17190 200g 4 22920 100g - In what year will you have half of the amount of radioactive material than what you started with (assuming that the decay process starts today)? - 7737 • How many years will it take to have 25% of what you started with? • 11,460 years