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Nuclear Chemistry

Nuclear Chemistry. Chapter 4.4: Unstable Nuclei & Radioactive Decay Chapter 24: Nuclear Chemistry. ATOMIC REVIEW:. Atomic number = # of protons # of neutrons = mass # - atomic # protons & neutrons are in the nucleus. 12. 12. C. C. 6. ATOMIC REVIEW:.

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Nuclear Chemistry

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  1. Nuclear Chemistry Chapter 4.4: Unstable Nuclei & Radioactive Decay Chapter 24: Nuclear Chemistry

  2. ATOMIC REVIEW: • Atomic number = # of protons • # of neutrons = mass # - atomic # • protons & neutrons are in the nucleus

  3. 12 12 C C 6 ATOMIC REVIEW: • isotopes have different # of neutrons • there are 3 forms of isotope notation carbon-12

  4. NEW TERMS: • Nucleon = term for all protons & neutrons • Strong nuclear force short-range force among nucleons • Increases with shorter distance • NOT the same as an electric force

  5. Stable vs. Unstable • Stable nuclei no spontaneous changes • Unstable nuclei spontaneously changes to become a nucleus of a different element

  6. Transmutation • Unstable nuclei are naturally “built wrong” and “fall apart” • An unstable nucleus undergoes transmutation, changing from one element into another • the nucleus changes # of protons!

  7. Why? • Radioactivity of an atom depends on the ratio of neutrons (N) to protons (P) • How is a nucleus held together? • STRONG NUCLEAR FORCE

  8. Why? • Think about it! . . . protons are all positively charged and want to repel each other • Neutrons act as a “nuclear glue” – they increase the strong nuclear force but don’t repel because they have no charge

  9. Band of Stability • N/P ratio of stable nuclei (page 866) • Stable small atoms are near 1/1 ratio • Stable large atoms are near 1.5/1 ratio • Predict the stability of the following: carbon-12 hydrogen-3 • mercury-200 • uranium-238

  10. Discovery • In the 1900’s only 3 radioactive elements were identified • Today, all elements after bismuth are radioactive • The larger they are, the more easily they “fall apart”

  11. Radiation Types 1. Alpha () particles 2. Beta () particles 3. Gamma () rays 4. Positron emission 5. Electron Capture (EC) . . . and more Nuclear reactions have BALANCED nuclear equations!!

  12. 4 4 2 2 206 4 210 Po  Pb + He 82 2 84  Particle • it is a helium nucleus • symbol: He or  • low energy – doesn’t penetrate foil • decreases the # of protons • never emitted with beta

  13. 0 0 -1 -1 14 14 C  N + e 0 6 7 -1  Particle • it is an electron (from the nucleus) • symbol: e or  • higher energy - penetrates the skin • increases # of protons • never emitted with alpha

  14. 238 234 4 U  He + Th + 2  0 92 90 2 0  Ray • high energy electromagnetic wave • no mass and no charge • higher energy – blocked only by thick lead or thick concrete • used to treat cancer • usually is emitted with alpha or beta

  15. 0 +1 0 1 -1 0 Positrons or Electron Capture • Positron emission  e • decreases # of protons • Electron Capture, EC  e (reactant side of equation) • decreases # of protons • Neutron captured or emitted  n

  16. Fission & Fusion • Nuclear Fission – the splitting of a nucleus into fragments • Very large release of energy • Used in nuclear power plants

  17. Fission & Fusion • Nuclear Fusion – the combining of atomic nuclei • Very large release of energy • Occurs in the core of the sun & other stars • Requires high temperatures (5 million K) • Atomic explosions initiate fusion, but can’t be controlled • . . . and many more!

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