1 / 47

Topic 12 Nuclear Chemistry

Topic 12 Nuclear Chemistry. What is Radioactivity?. Isotopes of many atoms are unstable (have extra energy). These are called radioisotopes. Radioisotopes emit this extra energy (radiation), to become more stable, by splitting up (fission).

gholston
Download Presentation

Topic 12 Nuclear Chemistry

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Topic 12 Nuclear Chemistry

  2. What is Radioactivity? Isotopes of many atoms are unstable (have extra energy). These are called radioisotopes. Radioisotopes emit this extra energy (radiation), to become more stable, by splitting up (fission). When a radioisotope splits up new atoms with different atomic and mass numbers are formed. Radioisotopes that emit radiation are radioactive. The emission process is called radioactivity. Radioactivity is a totally random (spontaneous) process. It cannot be predicted as far as which atoms will decay; however, the overall half-life of radioisotopes is well known.

  3. Historical Background • Wilhelm Roentgen – discovered x-rays • Henri Becquerel – found Uranium ores emit radiation that resembled x-rays • Marie & Pierre Curie – isolated two new elements (Po & Ra) from uranium ores • Ernest Rutherford - showed there were 3 types of radiation , , and  *The Curies’ & Becquerel were jointly awarded the Nobel prize in Physics for discovering Radioactivity in 1903 *In 1911 Marie Curie won a second Nobel prize in Chemistry for isolation of pure radium metal

  4. Nuclear Chemsitry - nucleus neutrons electrons unstable Size of the nucleus Ratio of protons to neutrons

  5. Nuclear Belt of Stability • Protons repel each other- The higher the atomic number is, the greater the repulsion among protons, making the nucleus unstable. • Neutrons help to stabilizethe nucleus • As the number of protons increases, the number of neutrons needed to keep the nucleus stable increases • Stable atoms have a ratio of neutrons to protons that falls in the belt of stability

  6. There are no stable isotopes of elements above atomic number 83. Only certain combinations of protons and neutrons are stable. A nuclide falling outside the “belt of stability” are radioactive. They spontaneously decay to form another element.

  7. Nuclear Belt of Stability

  8. Radioactive Particles (emissions) • A radioisotope can lose energy by emitting three different types of radiation; refer to Table O

  9. Alpha particles have the lowest penetrating power, gamma the highest. Alpha particles won’t pass through paper. Alpha particles have the highest ionizing power. They knock off electrons and leave a trail of ions as they pass through the air.

  10. Separation of Radioactive Emissions • Electromagnetic Field • Opposites charges attract

  11. Types of Nuclear Reactions A. Transmutations–when one atom changes into another more stable atom • When a nucleus emits radiation, the # of protons changes, and so the element changes • Transmutations can be natural (spontaneous) or artificial(induced)

  12. Natural just happens (ordinary decay of an unstable isotope). Radioisotopes that spontaneously decay are listed on reference table N. • Induced means to bombard nuclei with high NRG particles (nuclear bullets) to make it unstable (like a nuclear reactor).

  13. Each radioactive isotope has a specific mode and rate of decay (half-life).

  14. This decay can be written in the form of a nuclear equation. • the MASS AND CHARGE must be balanced on both sides of the equation • nuclides decay to achieve a stable ratio of neutrons to protons

  15. Writing Nuclear Equations • Use Table N & O • Mass and Charge must be balanced on both sides of the equation

  16. Changes in Mass Number and Atomic Number That Occur When Radioactive Elements Decay

  17. 1. Natural Decay: spontaneous

  18. daughter nuclide parent nuclide Decay Modes • Alpha emission: mass decreases by four, atomic number decreases by two. alpha particle • 238U undergoes alpha decay The total mass on the left must equal the total mass on the right (238 = 4 + 234) The total charge on the left must equal the total charge on the right (92 = 2 + 90)

  19. electron Decay examples continued • Beta Emission: mass remains the same, atomic number increases by one. • The total mass on the left must equal the total mass on the right (234 = 0 + 234) • The total charge on the left must equal the total charge on the right (90 = -1 + 91)

  20. positron Decay examples continued • Positron Emission: mass remains the same, atomic number decreases by one. • The total of the mass numbers on the left must equal the total on the right (37 = 0 + 37) • The total charge on the left must equal the total charge on the right (19 = 1 + 18)

  21. 2. Artificial Decay • particle accelerators give charged particles enough energy to overcome electrostatic forces & penetrate the nucleus of an atom • There will be 2 reactants (a target nuclei and a particle “bullet”) • Ex 1. • Ex 2 X is _______ Remember…Mass & Charge must be equal neutron, beta, or alpha particle Nuclear bullet Let’s practice……RB pg 217-220 #’s 1-15; guide pg 6

  22. 4. Half-Life • The amount of time that it takes for 1/2 a sample to decay. • radioactivity of a sample deceases over time but neverreaches zero • each time a decay happens, one more of the original radioactive nuclei has disappeared • as the unstable nuclei steadily disappear, the activity of the whole also decreases. Therefore, the older the sample, the less radiation it will emit (shorter ½ life, less stable it is) Half-Life

  23. Each radioactive isotope has a particular rate at which it decays. See reference Table N for sample radioisotopes • The half-life or rate of decay is CONSTANT (STAYS THE SAME) regardless of the sample size, or other physical conditions (temperature or pressure). Decay of 20.0 mg of 15O. What remains after 3 half-lives? After 5 half-lives?

  24. Half Life Calculations • Doing calculations, use chart or arrows and always start time with zero.

  25. Practice problems Ex 1) How much phosprous-32 (P-32) is left after 3 half-lives if the original sample contained 200 mg? Using Chart: start time with zero As you go down, mass amount decreases by 1/2 Using Arrows (represent a ½ life passing): 0 1 2 3 200mg 100 mg 50 mg 25 mg

  26. Half-life problems • Use this formula (½)t/T from Table T if the question states “what fraction or percentage”, otherwise              • use   t/T = # of half-life cycles from Table T

  27. Example #1 • What mass of iodine-131 remains 32 days after a 100-g sample of this  isotope is obtained? • Use t/T = # of half-life cycles and Reference table N to find T, then find mass • 32 d/8.07 d =4 half-life cycles • Cut the 100 g in half 4 times • 100502512.56.25g is the answer!

  28. Example #2 • The starting mass of a radioactive isotope is 20.0 g. The half-life period of this isotope is 2 days. What percentage of the original amount remains after 14 days? • Use this formula (½)t/T • (½)14d/2d = (½)7 ½ x ½ x ½ x ½ x ½ x ½ x ½ = 1/128 x100 = 0.78% is the answer!

  29. Part 2 – Nuclear Energy- Conservation of matter to energy • The total amount of matter and energy cannot be destroyed. • The loss of mass in nuclear reactions represents a conversion of some matter into energy • The matter that has been converted into energy is called the mass defect

  30. 5. Nuclear Changes: Converting Matter to Energy (known as MASS DEFECT) • Energy released in a nuclear reaction comes from the fractional amount of mass being converted to energy • Energy released during nuclear reactions is much greater than the energy released during chemical reactions • The basics of nuclear energy – YouTube • http://www.powerhouseanimation.com/PRG/PHYS025.swf

  31. a) Nuclear Fission: splitting atoms • bombarding the nucleus of a heavy atom with neutrons- this splitsthe big atom into two smaller atoms and releasing some neutrons and atremendous amount of energy • Used in power stations (NRG produced is used to heat water that drives steam turbines) • the neutrons released in the reaction can cause additional chain reactions (diagram of reaction) • an uncontrolled chain reaction results in a nuclear explosion (atomic bomb) • a controlled chain reaction can be used as a source of energy (nuclear reactor)

  32. Fission = splitting atoms

  33. Figure 19.6: Diagram of a nuclear power plant.Nuclear Power Plant

  34. Nuclear Fission & POWERfukushima • Currently about 103 nuclear power plants in the U.S. and about 435 worldwide. • NRC: List of Power Reactor Units Nuclear Regulatory Commitee • 17% of the world’s energy comes from nuclear.

  35. Nuclear power plants in operation in the U.S. in 2002.

  36. b) Nuclear Fusion • Two light isotopes cometogether (combine) (fuse together) releasing a lot of energy • this happens naturally in stars (hydrogen fusing together to form helium). Ex 3: 3He + 1H → 4 He + 0 e + energy 2 1 2 1 Ex 2: 3H + 3H → 4 He + 2 1 n + energy 2 2 2 0

  37. Nuclear = 19 % of US electrical energy use. danger of nuclear reactor meltdown (safety risks) Reactor releases toxic wastes to the environmentCan get into food chain- Long-term storage of nuclear waste (½ life)!! fuel is abundant no toxic waste (cleaner) High energy requirements- not yet sustainable - in order for nuclei to combine they need enough energy to overcome the forces of repulsion between like charges Fission vs. Fusion F I S S I ON FUSION

  38. Nuclear Weapons • Atomic Bomb • chemical explosion is used to form a critical mass of 235U or 239Pu • fission develops into an uncontrolled chain reaction • Hydrogen Bomb • chemical explosion  fission  fusion • fusion increases the fission rate • more powerful than the atomic bomb

  39. Uses of Radioisotopes I II III

  40. BEIR V, National Academy Press, 1990 Radiation = mostly natural (82%)

  41. Single and Repeated Exposures Have Impact • the effects of nuclear radiation on the body can add up over time.

  42. 6. Uses of Radioactive Materials 1. Radioactive Dating: C-14 (carbon dating) and U-238/Pb-206 (mineral/rock dating) 2. Industrial measurement (gamma rays) – to detect the thickness/strength of materials. 3. Sterilzation: kills/prevents bacteria and other disease causing organisms: Co-60 and Cs-137 and gamma radiation (food irradiation) • Fact.. • Irradiated milk has a shelf life of 3 mo. without refrigeration. • USDA has approved irradiation of meats and eggs.

  43. Radiation treatment using -rays from cobalt-60. 4. Tracers in Medicine: • Quickly eliminated and have short half-lives • Treating disorders and disease I-131 (thyroid), Tc-99 (brain tumors) 5. Radiotherapy – gamma rays to kill cancer cells or Ra-226 and Co-60 (cancer therapy) 6. Nuclear power – radioactive decay produces energy in the form heat which later helps to produce electricity Fissionable fuels: Pu-239 & U- 235 • ***Fact...Tc -99 is probably the most widely used radioisotope • in medicine today; it is a decay product, of molybdenum-99.

  44. 7. Risks and Hazards of Radioactivity • Harms living cells • Damages/destroys cells • Lower doses give rise to mutant cells causing cancer (ionizing molecules) • Higher doses can cause radiation sickness • Radioactive waste must be stored safely • Burying radioactive wastes from nuclear power plants (Cs-137, N-16, Kr-85, and Rn-222). Long half-lives • “NIMBY” syndrome- don’t bury the waste in my backyard. Where do we store these wastes so they don’t get into the food chain?

  45. 3. Nuclear Accidents affect the environment for many years afterwards • Safety issues concerning nuclear power plants • Chernobyl accident in Ukraine 1986 (contaminated farmland and livestock in Western Europe and North America) • Nuclear fallout damages people’s health causing cancer and perhaps death. Effects of Radiation……Let’s watch • http://www.kentchemistry.com/links/Nuclear/EffectsofRadiation.htm

  46. Uses of RadioisotopesRead pp226-227 and fill in chart & complete questions 48-57

More Related