1. Nuclear Chemistry Mrs. Stoops Chemistry

2. Nuclear reactions – Unstable isotopes gain stability by undergoing changes always accompanied by a large energy amounts given off. Not affected by temperature, pressure or presence of a catalyst. Radioisotopes have unstable nuclei Depends on ratio of neutrons to protons and size of nucleus 3 types of nuclear radiation: Alpha Beta Gamma

3. Alpha radiation –  helium nuclei has been given off alpha particle 4 2 He  2p + and 2n example: 238 92 U  234 90 Th + 4 2 He** reaction balanced Alpha particles do not travel very far They do not penetrate much Can cause damage if ingested

4. Beta radiation -  Electron is emitted Beta particle 0 -1 e -1 for atomic number; no mass Example: 14 6 C  14 7 N + 0 -1 e More penetrating than alpha

5. Gamma radiation -  High energy photon Given off with either beta or alpha particles Example: 230 90 Th  226 88 Ra + 4 2 He +  No mass No charge Doesn’t alter the atomic number or mass Extremely penetrating and very dangerous

6. Nuclear Transformations stable nuclei have roughly equal number of neutrons and protons neutron – proton ratio determines the type of decay that occurs Beta emission – when too many neutrons – beta is given off Electron capture – other nuclei are unstable due to too few neutrons o 37 18 Ar + 0 -1 e  37 17 Cl Positron emission – proton changes to neutron o 8 5 B  8 4 Be + 0 +1 e

7. All nuclei with atomic numbers greater than 83 are radioactive they have too many neutrons and too few protons most emit alpha emissions o 226 88 Ra  222 86 Rn + 4 2 He If all masses were measured accurately, a small amount of mass is lost and changed to energy during radioactive decay

8. Half-Life All radioisotopes have characteristic rates of decay. Half-life is the time it takes for ½ of the nuclei in the sample to decay Can be short or long time periods Ex oCarbon-14 = 5730 years oRadon = 2223.8 days oU-238 = 4.46 x 10 9 years Many artificially prepared radioisotopes have short half-life which is useful in medicine. Age dating – is done by determining the amount of carbon-14 remaining in a material.

9. Transmutation Reactions Conversion of an atom of 1 element to another element. 2 ways to occur: oRadioactive decay oParticles bombard the nucleus (p, n,  ) Occur in nature or artificially Rutherford – earliest bombardment o 14 7 N + 4 2 He  18 9 F which then becomes 18 9 F  17 8 O + 1 1 H Elements above 92 are called transuranium and all undergo transmutation

10. Fission & Fusion Fission Nuclei are bombarded with neutrons They split into smaller fragments U-235 and Pu-239 are only ones that are Fissable Neutrons released will go on to strike others causing a chain reaction. Enormous amounts of energy released

11. Example: 235 92 U (& n)  236 92 U (unstable)  91 36 Kr + 146 56 Ba (& 3 n) + E Uncontrolled results in a bomb Controlled in reactors to produce energy (nuclear power)

12. Fusion Energy from the sun is produced via fusion Nuclei combine to produce a greater mass In the sun – 2 1 H + 3 1 H  4 2 He + 1 0 n + energy Very high temperature needed to start reaction (40 million degrees)

13. Uses of radiation Agriculture – tracers to test affects of chemicals Medicine – detect and treat tumors, conditions, etc oThyroid problems oTumors oRadiation therapy