Basics of Nuclear Chemistry: The Nucleus, Isotopes, and Radioactivity

1. Nuclear Chemistry

2. The Nucleus • Remember that the nucleus is comprised of the two nucleons, protons and neutrons. • The number of protons is the atomic number. • The number of protons and neutrons together is the mass number which is effectively the mass of the atom.

3. Isotopes • Not all atoms of the same element have the same mass due to different numbers of neutrons in those atoms. • There are three naturally occurring isotopes of uranium: • Uranium-234 • Uranium-235 • Uranium-238

4. Radioactivity • It is not uncommon for some nuclides of an element to be unstable, or radioactive. • We refer to these as radionuclides. • There are several ways radionuclides can decay into a different nuclide.

5. Types ofRadioactive Decay

6. 238 92 234 90 4 2 4 2 He U Th He +  Alpha Decay: Loss of an -particle (a helium nucleus)

7. 131 53 0 −1 I 0 −1 0 −1 0 −1 0 −1 1 1 1 1 1 0 e p e p n e e Xe 131 54  + + +   or Beta Decay: Loss of a -particle (a high energy electron) This occurs because a neutron is converted to a proton and a high energy electron (b particle). 130 53 I with 

8. 11 5 11 6 0 1 0 1 1 0 1 1 0 1 e e C B e p n +  +  Positron Emission: Loss of a positron (a particle that has the same mass as but opposite charge than an electron) This occurs because a proton is converted to a neutron and the positron.

9. 0 0  Gamma Emission: Loss of a -ray (high-energy radiation that almost always accompanies the loss of a nuclear particle as that particle reorganizes into a more stable arrangement)

10. 0 −1 81 37 1 1 1 0 81 36 Rb + e Kr n p +   Electron Capture Addition of an electron (from the element’s own orbitals) to a proton in the nucleus • As a result, a proton is transformed into a neutron. 0 −1 e