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CHAPTER 25 Nuclear Chemistry

CHAPTER 25 Nuclear Chemistry. I. The Nucleus -Terms (p. 798-820). I. II. III. IV. Ionizing Radiation. Radiation is a form of energy transferred by waves or atomic particles

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CHAPTER 25 Nuclear Chemistry

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  1. CHAPTER25 Nuclear Chemistry I. The Nucleus -Terms (p. 798-820) I II III IV

  2. Ionizing Radiation • Radiation is a form of energy transferred by waves or atomic particles • Ionizing Radiation is any radiation with high enough energy to create ions (by knocking electrons out of atoms) like UV, X, gamma, and cosmic rays • There are both natural sources of radiation (unstable nuclei and stars) and human created sources

  3. Zone of Stability • Stable nuclei exist within the “zone of stability” seen on the graph…not always a 1:1 ratio of p+ to no • Outside this range, nuclei are unstable and will decay (disintegrate) into new nuclei

  4. Definitions • Nucleons = particles in nucleus (p+ and n0) • Nuclide refers to the nucleus of an atom • Nuclear Reactions involve transmutation where one element become another. • Radioactive Decay is the when unstable nuclei spontaneous lose energy by emitting ionizing particles; as this changes the nucleus of the atom, this also changes the type of element

  5. Alpha Decay Process Daughter Nuclide Np-237 Th-234 Ra-228 Rn-222 •  Parent Nuclide Am-241 U-238 Th-232 Ra-226 Alpha Particle (Helium Nucleus) (4.00147 amu)

  6. A. Mass Defect • The mass defect describes the mass lost during the formation of nuclei • Difference between the mass of an atom and the mass of its individual particles. 4.00260 amu Mass of atom 4.03298 amu Mass of particles

  7. B. Nuclear Binding Energy • Energy released when a nucleus is formed from nucleons. This contributes to the loss in mass of nucleus, described by E = mc2. • High binding energy = stable nucleus. E = mc2 E: energy (J) m: mass defect (kg) c: speed of light (3.00×108 m/s)

  8. B. Nuclear Binding Energy Iron (Fe) is the most stable nucleus!! Unstable nuclides are radioactive and undergo radioactive decay.

  9. CHAPTER25 Nuclear Chemistry II. Radioactive Decay (p. 798-820) I II III IV

  10. Types of Spontaneous Radiation stopped by… Greek symbol charge • Alpha particle () • helium nucleus paper 2+ • Beta particle  or - • electron 1- wood • Positron + • positron 1+ Lead or concrete • Gamma () • high-energy photon 0

  11. Other Radiation particles Greek symbol charge • proton p+ +1 • neutron n0 0

  12. How does an electron get emitted from the nucleus? • Basically a neutron splits into a proton which stays in the nucleus and an electron is emitted ( decay) - + + - + + + n converted to a proton and an e is emitted n & p in nucleus n is “really” like a p and e together

  13. parent nuclide alpha particle daughter nuclide Transmutation Reactions • I Alpha Emission Numbers must balance on both sides of arrow!! 238amu on left = (234 + 4amu) 92 is nucl chrg on left = 90 + 2 on right

  14. electron positron B. Nuclear Decay • II Beta Emission • III Positron Emission *a proton 1p is not the same as a positron 0e

  15. electron B. Nuclear Decay • IV Electron Capture

  16. Alpha capture B. Nuclear Decay • V Alpha Capture followed by neutron emission • Gamma Emission causes no change in mass or charge and… • Usually follows the previous types of decay.

  17. Beta (Negatron) Decay Process Daughter Nucleus Osmium-187 Calcium-40  Antineutrino Parent Nucleus Rhenium-187 Potassium-40  Beta Particle (electron)

  18. Beta Particles • Same as an electron with kinetic energy • Positive or negative charge of 1 • May be positively or negatively charged • Can normally be stopped by 1 cm of plastic, wood, paper • Exception for positron emitters

  19. B. Nuclear Decay • Why nuclides decay…pg. 803 • need stable ratio of neutrons to protons DECAY SERIES TRANSPARENCY

  20. C. Half-life • Half-life (t½) • Time required for half the atoms of a radioactive nuclide to decay. • Shorter half-life = less stable.

  21. C. Half-life mf:final mass mi:initial mass n:# of half-lives

  22. C. Half-life • Fluorine-21 has a half-life of 5.0 seconds. If you start with 25 g of fluorine-21, how many grams would remain after 60.0 s? GIVEN: t½ = 5.0 s mi = 25 g mf = ? total time = 60.0 s n = 60.0s ÷ 5.0s =12 WORK: mf = mi (½)n mf = (25 g)(0.5)12 mf = 0.0061 g

  23. Decay Series Many heavy elements are unstable and so they will continue to decay (be radioactive) until they finally transmute into a stable nucleus. Here is an example of the Th-232 decay series Thorium oxide is used to in camping lanterns to intensify the brightness when on fire. Stable isotope

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