1. Unstable Nuclei and Radioactive Decay

2. Radioactivity (Radioactive decay) The process by which some substances spontaneously emit radiation. Radioactive atoms emit radiation because their nuclei are unstable. This loss of energy (radiation) allows the unstable atoms to gain stability. By emitting radiation, an unstable atom of one element changes into a stable atom of another element.

3. Types of Radiation Scientists identified 3 types of radiation by applying an electric field to radiation from a radioactive source. Figure 4.5 on page 124

4. Alpha Radiation Deflected toward the negatively charged plate Made of alpha particles Each particle contains 2 protons and 2 neutrons Has a 2+ charge Equivalent to a helium-4 nucleus Represented by α or Nuclear equation =

5. Beta Radiation Deflected toward the positively charged plate Made of beta particles Each particle is a fast moving electron Has a 1- charge Mass = Mass of electron (1/1840 amu) Represented by β or Nuclear equation =

6. Gamma Radiation Accounts for most of the energy lost during radioactive decay Not deflected by electric or magnetic charges Made of massless high energy rays Possess no electrical charge Represented by γ Nuclear equation = n + 6 Li = 7 Li + γ

7. Nuclear Stability Primary factor in determining nuclear stability is the ratio of neutrons to protons. An atom with too many or too few neutrons is unstable. These atoms radioactively decay until they form stable atoms with appropriate neutron to proton ratios.