Nuclear Chemistry

1. Nuclear Chemistry Brown, LeMay Ch 21 AP Chemistry Monta Vista High School To properly view this presentation on the web, use the navigation arrows below andleft-click on each page to view any animations.

2. 21.1: Radioactivity • Result of unstable nuclei Nucleons: particles in the nucleus, nand p Radioisotopes: atoms that containing radioactive nuclei (called radionuclides) Nuclear reactions or equations: express products of radioactive decay, fusion, or fission Radioactive decay: process in which a radionuclide spontaneously decomposes

3. 4 2+ He 2 238 4 234 U He Th 92 2 90 Most common types of radioactive decay A few cm; cannot penetrate human skin a energized He nucleus alpha +

4. Alpha decay

5. 131 Xe 54 0 0 0 e e e -1 -1 -1 131 1 1 I n p 53 0 1 Radioactive decay b ~300 cm; can penetrate skin, but rarely beta High energy electron + A neutron converts to a proton and electron +

6. 0 0 g g 0 0 244 * Pu 94 244 Pu 94 Radioactive decay g Very far; can be stopped by ~5 cm of Pb gamma photon + • Represents energy emitted (i.e., radiation) when nucleons in an unstable radionuclide reorganize to become more stable • Usually not written in a nuclear reaction.

7. 11 B 5 0 0 0 e e e 1 1 1 1 11 1 C p n 6 1 0 Radioactive decay • Antimatter (positively charged) e; collides with e- and both are annihilated as gamma rays are created positron + A proton converts to a positron and neutron +

9. 81 Kr 36 0 0 0 e e e -1 -1 -1 1 81 1 p Rb n 1 37 0 Radioactive decay Electron capture • Capture of inner shell e- by nucleus + A proton and electron convert to a neutron +

10. 21.2: Nuclear stability Strong nuclear force: pulls nucleons together to form nuclei (actually acts on quarks) * Weak nuclear force: responsible for changes in flavor of quarks • Nuclei become unstable (radioactive) if the neutron-to-proton ratio “strays” too far from “normal range” • * Nuclear shell model: when p and n fill nuclear shells, atoms are unusually stable: “Magic numbers” 2, 8, 20, 28, 50, 82, 126

11. A radionuclide will decay until a stable ratio exists: • If too many n, nwill be converted to pby b emission. • If too few n, pwill be converted to nby positron emission or electron capture. • Nuclei with p≥ 84 undergo a emission 1

12. 21.4: Rates of Decay Half-life (t½): • Time for ½ a radioactive (i.e., having an unstable p/n ratio) material to decay (form 2 or more stable atoms)

13. 21.6: Mass-energy relationships DE = Dm c2 (mass in kg) Mass → energy • Mass lost during radioactive decay is released as energy Energy → mass • Mass defect (Dm): mass difference between a nucleus and its constituent nucleons; the nuclear binding energy must be added to a nucleus to break it into its nucleons • When energy is added, the nucleons separate and gain mass

14. 139 94 1 Ba + Kr + 3 n + energy 56 36 0 1 235 n + U 0 92 21.7& 21.8: Fission & Fusion Fission: splitting of a nucleus; some mass is lost, which results in release of energy (ex: nuclear power plants, “atomic” bombs)

15. 1 0 4 n + energy He + 2 3 2 H + H 1 1 Fusion: combination of 2 nuclei; some mass is lost, which results in release of energy (ex: stars, “H” bombs)

16. Inc Mass ↓ Q = -1/3 Q = 2/3 Down (d) Up (u) Strange (s) Charm (c): discovered 1974 at 1.5 GeV Bottom (b): discovered 1978 Top (t) The Standard Model of the Atom 6 flavors of quarks:

17. Ordinary matter is made of: p+: u-u-d quark triplet n0: u-d-d quark triplet e-: one of 6 leptons b decay: d quark in a nchanges into u quark, making a p