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Chemistry Chapter 4 Notes #3 (Sec 4) Unstable Nuclei Nuclear Reactions – Rxns that involve a change in the nucleus of an atom (most only involve e- changes) Radioactivity – When substances spontaneously emit radiation Radiation – Rays and particles emitted by radioactive material Unstable Nuclei By emitting radiation atoms of one element can change into atoms of another element This happens because the nuclei is unstable Atoms gain stability by losing energy (ex. Pencil falling over) Unstable Nuclei Unstable nuclei will lose energy by emitting radiation in a spontaneous process (so it doesn’t require energy) called radioactive decay They undergo decay until they form stable non-radioactive atoms of a different element. Radiation-Alpha Positively charged alpha particles – Deflected toward a negative plate – Alpha particle – 2 p+ and 2 n0 4 He or α – Symbol 2 Nuclear Equation shows atomic # and mass # of the particles involved Ex. Alpha decay- Radium-226 into radon-222 Radiation - Beta Negatively charged beta particles – Deflected toward a positive plate -with a -1 charge – symbol: 0-1ß Ex. Carbon-14 into Nitrogen-14 Radiation - Gamma Not deflected by electric or magnetic fields High energy radiation with no mass accompanies alpha and beta radiation Denoted by the symbol: 00У Unstable Nuclei Atoms containing too many or too few neutrons are considered unstable Stability is based on the ratio of neutrons to protons The END!