Nuclear Chemistry Review & Calculations

1. Nuclear Chemistry Review & Calculations Ms. Sipe

2. Nuclear Chemistry Reactions in the nuclei of atoms • Nuclear reactions • Changes in the nuclei • Involve the emission of energy- rays or particles • Not affected by temperature, pressure , or catalysts like regular chemical reactions • In chemical rxns bonds break and rearrange to form new substance (reactivity based on what subatomic particle?)

3. Nuclear Chemistry Types of nuclear reactions • Fusion- combining of nuclei, releases a lot of energy • Stars and the sun • Fission- splitting of nuclei into smaller nuclei • Radioactive Decay or radioactivity • Reactions begin with unstable isotopes called radioisotopes that undergo change to become stable

4. Nuclear Fusion The energy emitted by the sun results from nuclear fusion. • Fusion occurs when nuclei combine to produce a nucleus of greater mass. • In solar fusion, hydrogen nuclei (protons) fuse to make helium nuclei. A LOT OF ENERGY PRODUCED! The reaction also produces two positrons.

5. Neutron 235 92 236 92 3 n 1 0 U Uranium-235 (fissionable) U Uranium-236 (very unstable) 142 56 91 36 Ba Barium-142 Kr Krypton-91 Nuclear Fission The figure below shows how uranium-235 breaks into two smaller fragments of roughly the same size when struck by a slow-moving neutron. More neutrons are released by the fission. These neutrons strike the nuclei of other uranium-235 atoms, which cause chain reactions.

6. Recap: Fusion vsFission • Combining 2 light nuclei to form a heavier nucleus • Requires high T & P • Powers stars & sun • Splitting a heavy nucleus into 2 nuclei with smaller mass # • Radioactive decay (w/o neutron)

7. Types of Nuclear Emissions/Radiation

8. Radioactive decay 234 90 Th + 4 2 He (a emission) 238 92 U Thorium-234 Alpha particle Uranium-238 Alpha Radiation Mass # decreases by 4 & Atomic # decreases by 2

9. → 14 7 N + 0 –1 e (b emission) Nitrogen-14 (stable) 1 1 p + Beta particle 1 0 14 6 C n Carbon-14 (radioactive) Neutron Proton → 0 –1 e Electron (beta particle) Beta Radiation An electron resulting from the breaking apart of neutrons in an atom # of protons increases while #of neutrons decreases. Same Mass #; Atomic # increases by one

10. 230 90 Th → 226 88 Ra + 4 2 He + g Alpha particle Gamma ray Thorium-230 Radium-226 234 90 Th → 234 91 Pa + 0 –1 e + g Thorium-234 Protactinium-234 Beta particle Gamma ray Gamma Radiation • Nuclei often emit gamma rays along with alpha or beta particles during radioactive decay. • Gramma ray – no mass/no electric charge - Does not alter the atomic number or mass number of an atom.

11. Balancing Nuclear Equations U-238 alpha decay- Helium particle emitted 23892U ? + 23490Th Na -24 beta decay- electron emitted 2411Na ? + 2412Mg

12. Balancing Nuclear Equations U-238 alpha decay- Helium particle emitted 23892U 42He + 23490Th Na -24 beta decay- electron emitted 2411Na 0-1e + 2412Mg

13. Nuclear Chemistry Application of Radioisotopes • Smoke Detectors • Food Irradiation • Archaeological Dating • Medical Uses • Nuclear Power • Nuclear Weapons

14. Applications of Nuclear Reactions Nuclear power and Nuclear weapons Most common nuclear fuel: Uranium-235, Plutonium-239 Difference btw power & weapon Power – can control E release & convert to heat Weapon – uncontrolled release of E

15. Power • Nuclear energy – Fr ~80%, US 20%, Japan 35%, Germany – 30% Weapon • Fission weapons – Atomic bombs (A-bomb) • Fusion weapons – Hydrogen bombs (H-bomb) • Manhattan Project WWII • Submarines – that use nuclear energy stay longer underwater

16. A Few Pros and Cons • No more need for oil • Not using fossil fuel • Fission > energy compared to gasoline • Will have unlimited amounts of energy (esp if fusion works; sun) • No need for us to depend on other countries • Hard to control • Nuclear waste • Pollution • Radiation • Nuclear reactor – away from large population, waterways, earthquake zones • Japan reactor explosion – then cooling system fails so further explosion or leak of radioactive material can occur • Nuclear reactor overheating – explode like a nuclear weapon • Nuclear weapon – destructive potential

17. A half-life (t½) is the time required for one-half of the nuclei in a radioisotope sample to decay to products. After each half-life, half of the original radioactive atoms have decayed into atoms of a new element.

18. Half-Life Half-lives can be as short as a second or as long as billions of years. Comparing Half-Lives

19. Half-Life Uranium-238 decays through a complex series of unstable isotopes to the stable isotope lead-206. Comparing Half-Lives • The age of uranium-containing minerals can be estimated by measuring the ratio of uranium-238 to lead-206. • Because the half-life of uranium-238 is 4.5 × 109 years, it is possible to use its half-life to date rocks as old as the solar system.

20. Half Life Calculations The half-life of beryllium-11 is 13.81 seconds. Let's say you start with 16 grams of 11Be. After 13.81s, you have 8 grams of that isotope left (the rest will have decayed to something else). After another 13.81s, you have 4 grams left; 13.81 seconds more, and you have 2 grams left……so after 3 half lives berllium-11 decayed from 16g to 2 g. In chemistry, you set up tables like this:

21. Practice Problem… In a particular bone sample, you have 80g of a parent and 560g of a daughter isotope. The half life of the sample is 100 years. How old is the bone? 560g + 80g = 640 g for the original parent 640  320  160  80 equals 3 half lives (3)(100 yrs) = 300 years old Now, you try some…

22. Closure: Germany said it would close all of its 17 nuclear reactors by 2022, a sharp policy reversal that will make it the first major economy to quit atomic power in the wake of the nuclear crisis in Japan. Do you think USA should do the same? • Provide 3 reasons to support your answer