1. Nuclear Chemistry

2. Radioactivity  Nuclear Reactions – reactions in which the nuclei of unstable isotopes (radioisotopes) gain stability by undergoing changes

3. Radioactivity  Henri Becquerel noticed that uranium ore exposed photographic film  Marie & Pierre Curie named the process radioactivity  The particles and rays emitted by a radioactive source are called radiation

4. Radioactivity  Radioactivity disproves Dalton’s theory of indivisible atoms  The stability of a nucleus depends on the relative proportion of neutrons to protons in the nucleus as well as the overall size of the nucleus  An unstable nucleus loses energy by emitting radiation during the process of radioactive decay

5. Types of Radiation  Alpha Radiation – consists of helium nuclei emitted from a radioactive source (alpha particles).  In nuclear equations, an alpha particle is written as

6. Types of Radiation  Beta Radiation – fast moving electrons formed by the decomposition of a neutron in an atom (beta particles)  In nuclear equations, beta particles are written as

7. Types of Radiation  Gamma Radiation – high energy electromagnetic radiation given off by a radioisotope  Often emitted along with alpha or beta radiation by the nuclei of disintegrating radioactive atoms

8. Types of Radiation Property Alpha Rad Beta Rad Gamma Rad Composition Alpha Particle Beta Particle Gamma Ray Symbol Charge2+1-0 Mass41/18370 Shielding Paper, clothing Metal foil Lead, concrete

9. Nuclear Stability and Decay  1500 nuclei are known. Of those, only 264 are stable and do not decay with time  In elements of low atomic number (less than 20), stable nuclei have roughly equal n 0 and p +  In elements of high atomic number, stable nuclei have more n 0 than p +

10. Nuclear Stability and Decay  The stable nuclei on a neutron vs proton plot are located in a region called the band of stability

11. Nuclear Stability and Decay  A nucleus may be unstable for several reasons:  Nucleus has too many neutrons relative to number of protons.  Decay occurs by turning a neutron into a proton and emitting a beta particle (electron) from the nucleus  Result: increase in p + and decrease in n 0

12. Nuclear Stability and Decay  Nucleus has too few neutrons relative to the number of protons.  Increase stability by converting a proton to a neutron by the nucleus capturing an electron

13. Nuclear Stability and Decay  Positron – a particle with the mass of an electron but with a positive charge. It may be emitted as a proton changes to a neutron

14. Nuclear Stability and Decay  All nuclei with atomic number 83 and higher are radioactive because they have too many n 0 and p + to be stable  Most emit alpha particles

15. Half-Life  Every radioisotope has a characteristic rate of decay measured by its half-life  Half-life – time required for one-half of the nuclei of a radioactive sample to decay to products

16. Transmutation Reactions  Transmutation – conversion of an atom of one element to an atom of another element.  Radioactive decay  Bombarding the nucleus with high-energy particles (p +, n 0, or α)

17. Transmutation Reactions  The elements with atomic numbers greater than 92 are called the transuranium elements  None occur in nature, and all are radioactive  Synthesized in nuclear reactors

18. Nuclear Fission  When the nuclei of certain isotopes are bombarded with neutrons, they undergo fission, the splitting of a nucleus into smaller fragments  Fission reactions generate additional neutrons, which lead to a chain reaction

19. Nuclear Fusion  Fusion occurs when nuclei combine to produce a nucleus of greater mass  Requires very high temperatures to start the reaction.  At these temperatures, matter exists as plasma, a high-energy state in which ions exist in a gaslike form