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CHEMISTRY 1 Nuclear Chemistry

CHEMISTRY 1 Nuclear Chemistry. Chapter 28. NUCLEAR CHEMISTRY. 1896- Antoine Becquerel discovered ___________________ He accidently left uranium ore on top of photographic plates. They became fogged from the exposure. Becquerel had 2 graduate students: _______________ _______________.

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CHEMISTRY 1 Nuclear Chemistry

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  1. CHEMISTRY 1Nuclear Chemistry Chapter 28

  2. NUCLEAR CHEMISTRY • 1896- Antoine Becquerel discovered ___________________ • He accidently left uranium ore on top of photographic plates. They became fogged from the exposure. Becquerel had 2 graduate students: _______________ _______________ radioactivity Marie & Pierre Curie

  3. Radioactivity • _______________________- the property by which uranium gives off rays • ______________________-penetrating rays emitted by a radioactive source. • In 1903, the Curies and Becquerel won Nobel prizes for this discovery. Radiation

  4. Types of Radiation • 1. Alpha emission -helium nuclei emitted from a radioactive source • 2 protons & 2 neutrons • 2+charge • Symbol is  • Don’t travel far and are not very penetrating • Stopped by a sheet of paper • Can’t penetrate skin, but dangerous if ingested • Very common with heavy nuclides He Write this

  5. Alpha Decay (α) Lose 2 protons (+2 charge) & 2 neutrons 4 2 He

  6. Examples: Mass # = # protons + # neutrons 238 U  ___ + He Th 92 Atomic # 222 Ra  Rn + He 86 Law of conservation of mass

  7. 226 88 4 2 Ra Rn + He 222 86 Atomic # 88 86 + 2 Mass # 226 222 + 4

  8. electrons • 2. Betaemission - fast moving ___________ formed by the decomposition of a neutron of an atom. The neutron breaks into a proton and an electron. The proton stays in the nucleus and the electron is ejected. (net effect: neutron changes into proton) • Write this: n  H + e

  9. Much smaller than alpha particles • Symbol is  • Charge is -1 • Much more penetrating than alpha particles • Stopped by aluminum foil or thin pieces of wood e Write this C N + e

  10. 0 -1 β Beta Decay (β) Lose electron (-1 charge, no mass) 14 6 C N + β 14 7 0 -1

  11. electromagnetic radiation • 3. Gamma emission - _________________ _____________ (high energy) emitted from a nucleus as it changes from an excited state to a ground energy state. • Often emitted along with  or  radiation • Symbol is  • Has no mass & no charge • High energy photon U He + Th + 2 

  12. the emission of gamma rays is one way that a nucleus with excess energy (in an excited nuclear state) can relax to its ground state • Extremely penetrating, very dangerous • Stopped somewhat by several feet of concrete or several inches of lead

  13. Gamma Emission (γ) No mass, no charge, loses just energy γ 0 0

  14. 4. Positron emission- ___________________________________ • e • Antimatter • Net effect: changes proton to a neutron • Occurs when neutron/proton ratio is too small Particle with the mass of an electron but a positive charge Write this (the 0 and the +1) Na  e + Ne

  15. Alpha radiation cannot penetrate the skin and can be blocked out by a sheet of paper, but is dangerous in the lung. Beta radiation can penetrate into the body but can be blocked out by a sheet of aluminum foil. Gamma radiation can go right through the body and requires several centimeters of lead or concrete, or a meter or so of water, to block it.

  16. Make sure you have both of these things: • Calculator • Periodic Table

  17. Nuclear Transformation (Transmutation)- ____________________________________ • bombarding with alpha particles • Bombarding with neutrons Changing one element into another N + He  O + H Write these U + n  U

  18. Fill in the blanks (not in your notes): 0 1 60 26 e • Co Ni + ____ • Am Np + ____ • Th He + ____ • N + ____ C + H 60 27 4 2 He 241 95 237 93 226 88 Ra 230 90 4 2 1 0 n 14 7 14 6 1 1

  19. Half-life (t1/2) • the time required for ½ of the atoms of a radioisotope to emit radiation and decay to products • the longer the half-life, the more _____________ the isotope • varies from fractions of a second to millions of years stable

  20. Examples • Nitrogen-13 decays to carbon-13 with a half-life of 10 minutes. How long is 4 half lives? 4 half lives X 10 min/half life = 40 min.

  21. If you start with 2.00 g of nitrogen-13 how many grams will remain after 4 half lives? 1 2 3 2.00 g 1.00 g 0.500 g 0.250 g 4 0.125 g

  22. Phosphorous-32 has a half-life of 14.3 yr. How many grams remain after 57.2 yr from a 4.0 g sample? 57.2 yr = 4 half-lives 14.3yr / half-life 1 2 3 4 4.0 g 2.0 g 1.0 g 0.50 g 0.25 g

  23. Carbon-14 dating • Carbon-14 is continuously produced in the ____________ when high energy neutrons from outer space collide with nitrogen-14 in the air. atmosphere N + n  C + H

  24. Carbon-14 combines with oxygen to form CO2 which is incorporated into plant materials. As long as the plant or animal is alive, decaying carbon-14 is continuously replaced. After death, the carbon-14 decays at a steady rate. Carbon-14 decays to Nitrogen-14 C  e + N

  25. The proportion of carbon-14 in the atmosphere is relatively constant. The carbon-14/carbon-12 ratio is used to identify the age of wood, cloth and other ______________ artifacts. The half-life of carbon-14 is _______________ years. • Only works for organic materials • Adjusted for change in % C-14 over the years organic 5730

  26. Example • If the C-14 in a fossil sample is only 1/4 what it is in living organisms, how old is the object? To have ¼ remaining, 2 half lives have passed. 2 X 5730 yr = 11,460 yr.

  27. Fission - splitting a heavy nucleus into two nuclei with smaller mass numbers. • used for _____________________ • production of ______________causes a chain reaction (which must be controlled) • 1 kg of uranium-235 is equivalent to 20,000 tons of dynamite nuclear energy n + U  Ba + Kr + 3 n neutrons

  28. FISSION: splitting of atoms Fission – splitting of atoms.

  29. heat steam • Fission in a nuclear reactor is carefully controlled. Much of the energy is _______. This energy is used to produce _________ and subsequently, __________________. • A _________________(usually water) is needed. • The water (or carbon) also acts as a moderator. It _____________the neutrons down so that they can be captured by the U-235 fuel. • Control rods made of _______________ are present to absorb excess neutrons to slow down the reaction. They can be raised or lowered into the reactor core. electricity coolant slows cadmium

  30. Fusion- combining two light nuclei to form a heavier, more stable nucleus • stars produce their energy this way • Currently __________________ are necessary in order to initiate fusion • possible future energy source high temperatures 4 H + 2e  He + energy

  31. FUSION: two nuclei combine to form a heavier nuclei Fusion – two nuclei combine to form a heavier nucleus.

  32. Proton-proton chain reaction Proton-proton chain reaction Fusion reaction in our Sun’s core.

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