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Nuclear Chemistry

Nuclear Chemistry. Introduction A. Isotopes. atomic number ( Z ). =. the number of protons. the number of protons. mass number ( A ). =. +. the number of neutrons. mass number ( A ). 12. C. 6. atomic number ( Z ). number of protons. 6. 12 – 6 = 6. number of neutrons.

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Nuclear Chemistry

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  1. Nuclear Chemistry

  2. IntroductionA. Isotopes atomic number (Z) = the number of protons the number of protons mass number (A) = + the number of neutrons mass number (A) 12 C 6 atomic number (Z) number of protons 6 12 – 6 = 6 number of neutrons

  3. IntroductionA. Isotopes Isotopes are atoms of the same element having a different number of neutrons.

  4. Nuclear vs Chemical Reactions • Nuclear reactions not affected by: • Temperature • Pressure • Catalysts • Nuclear reactions cannot be slowed, sped up or stopped

  5. IntroductionA. Isotopes • A radioactive isotope, called a radioisotope, is unstable and spontaneously emits energy to form a more stable nucleus. • Radioactivity is the nuclear radiation emitted by a radioactive isotope. • Of the known isotopes of all elements, 264 are stable and 300 are naturally occurring but unstable. • An even larger number of radioactive isotopes called artificial isotopes, have been produced in the laboratory.

  6. 4 He 2 IntroductionB. Types of Radiation • Types of radiation: alpha particles, beta particles, positrons, and gamma radiation. • An alpha (α) particle is a high-energy particle that contains 2 protons and 2 neutrons. • It has a +2 charge and a mass number of 4. alpha particle: a or

  7. 1 1 0 0 n p e e 1 0 −1 −1 IntroductionB. Types of Radiation • A beta (β) particle is a high-energy electron. • It has a −1 charge and a negligible mass compared to a proton. beta particle: β or • A β particle is formed when a neutron(n) is converted to a proton (p) and an electron (e). + neutron proton  particle

  8. 1 1 0 0 p n e e 0 1 +1 +1 IntroductionB. Types of Radiation • A positron is called an antiparticle of a β particle. • Their charges are opposite, but their masses are the same (i.e., effectively zero). • A positron has a +1 charge and is called a “positive electron.” positron: β+ or • A positron is formed when a proton is converted to a neutron. + proton neutron positron

  9. IntroductionB. Types of Radiation • Gamma rays are high-energy radiation released from a radioactive nucleus. • They are a form of energy, so they have no mass and no charge. gamma ray: g

  10. IntroductionB. Types of Radiation

  11. Radiation Penetrating Power www.anythingradioactive.com, updated 2018, accessed 5/3/2018

  12. Nuclear Reactions Radioactive decay is the process by which an unstable radioactive nucleus emits radiation. A nuclear equation can be written for this process: original nucleus new nucleus radiation emitted + The following must be equalon both sides of a nuclear equation: • The sum of the mass numbers (A) • The sum of the atomic numbers (Z)

  13. Nuclear ReactionsA. Alpha Emission Alpha emission is the decay of a nucleus by emitting an a particle.

  14. Nuclear ReactionsA. Alpha Emission HOW TO Balance an Equation for a Nuclear Reaction Write a balanced nuclear equation showing how americium-241 decays to form an a particle. Example Write an incomplete equation with the original nucleus on the left and the particle emitted on the right. Step [1] 241 4 He + ? Am 2 95

  15. Nuclear ReactionsA. Alpha Emission HOW TO Balance an Equation for a Nuclear Reaction Calculate the mass number and atomic number of the newly formed nucleus on the right. Step [2] 4 241 237 He + Np Am 2 95 93 mass number 241 − 4 = 237 atomic number 95 − 2 = 93 Step [3] Use the atomic number to identify the new nucleus and complete the equation.

  16. Nuclear ReactionsB. Beta Emission Beta emission is the decay of a nucleus by emitting a βparticle; 1 neutron is lost and 1 proton is gained.

  17. Nuclear ReactionsC. Positron Emission Positron emission is the decay of a nucleus by emitting a positron, β+; 1 proton is lost and 1 neutron is gained.

  18. Nuclear ReactionsD. Gamma Emission Gamma emission is the decay of a nucleus by emittingg radiation. • The g rays are a form of energy only. • Their emission causes no change in the atomic numberor the mass number. 99m 99 g + Tc Tc 43 43 • Technetium-99m is a metastable isotope; it decays by gamma emission to the more stable (but still radioactive) technetium-99.

  19. Nuclear ReactionsD. Gamma Emission Commonly, g emission accompanies a or β emission.

  20. Introduction

  21. Half-LifeA. General Features The half-life (t1/2) of a radioactive isotope is the time it takes for one-half of the sample to decay. The half-life of a radioactive isotope is a property of a given isotope and is independent of the amount of sample, temperature, and pressure.

  22. Half-LifeA. General Features

  23. Half-LifeA. General Features HOW TO Use a Half-Life to Determine the Amount of Radioisotope Present If the half-life of iodine-131 is 8.0 days, how much of a 100. mg sample remains after 32 days? Example Determine how many half-lives occur in the given amount of time. Step [1] 1 half-life 8.0 days 32 days x = 4.0 half-lives

  24. Half-LifeA. General Features HOW TO Use a Half-Life to Determine the Amount of Radioisotope Present For each half-life, multiply the initial mass by one-half to obtain the final mass. Step [2] 1 2 1 2 1 2 1 2 100. mg x x x x = 6.25 mg final mass initial mass The mass is halved four times.

  25. Half-Life A = amount Ao = initial amount n = number of half-lives n = number of half-lives t = total time t1/2 = half-life

  26. Half-LifeB. Archaeological Dating • Radiocarbon dating uses the half-life of carbon-14 to determine the age of carbon-containing materials. • The ratio of radioactive carbon-14 to stable carbon-12 is a constant value in a living organism. • Once the organism dies, the carbon-14 decays without being replenished. • By comparing the ratio of C-14 to C-12 in an artifact to the same ratio present in organisms today, the age of the artifact can be determined. • The half-life of C-14 is 5,730 years.

  27. Detecting and Measuring Radioactivity • The amount of radioactivity in a sample is measured by the number of nuclei that decay per unit time—disintegrations per second. • Common units include: 1 Curie (Ci) = 3.7 x 1010 disintegrations/second 1 Curie (Ci) = 1,000 millicuries (mCi) 1 Curie (Ci) = 1,000,000 microcuries (mCi) 1 becquerel (Bq) = 1 disintegration/second • Thus, 1 Ci = 3.7 x 1010 Bq.

  28. Detecting and Measuring Radioactivity • Radioactivity cannot be detected by the senses, yet it can have a powerful effect. • Nuclear radiation will damage or kill rapidly dividing cells such as bone marrow, skin, and the reproductive and intestinal systems. • Cancer cells divide rapidly as well, making radiation an effective treatment for cancer. • Food is irradiated, exposed to gamma radiation, to kill any living organism in the food. • Afterwards, the food is not radioactive, and has a considerably longer shelf life.

  29. Detecting and Measuring Radioactivity Several units are used to measure the amount of radiation absorbed by an organism. • The rad—radiation absorbed dose—is the amount of radiation absorbed by one gram of a substance. • The rem—radiation equivalent for man—is the amount of radiation that also factors in its energy and potential to damage tissue. • 1 rem of any type of radiation produces the same amount of tissue damage.

  30. Detecting and Measuring Radioactivity • The average radiation dose per year for a person is about 0.27 rem. • Generally, no detectable biological effects are noticed for a radiation dose less than 25 rem. • A single dose of 25–100 rem causes a temporary decrease in white blood cell count. • A dose of more than 100 rem causes radiation sickness—nausea, vomiting, fatigue, etc. • The LD50—the lethal dose that kills 50% of a population—is 500 rem in humans, while 600 rem is fatal for an entire population.

  31. Focus on Health and MedicineA. Radioisotopes Used in Diagnosis • Radioisotopes can be injected or ingested to determine if an organ is functioningproperly or to detect the presence of a tumor. • Technetium-99m is used to evaluate the gall bladder and bile ducts and to detect internal bleeding. • Thallium-201 is used in stress tests to diagnose coronary artery disease. • Using a scan, normal organs are clearly visible, while malfunctioning or obstructed organs are not.

  32. Focus on Health and MedicineA. Radioisotopes Used in Diagnosis

  33. Focus on Health and MedicineB. Radioisotopes Used in Treatment

  34. Focus on Health and MedicineC. Positron Emission Tomography • Positron emission tomography (PET) scans use radioisotopes which emit positrons whichenable scanning of an organ. • PET scans can detect tumors, coronary arterydisease, Alzheimer’s disease, and track theprogress of cancer. • A PET scan is a noninvasive method of monitoring cancer treatment.

  35. Focus on Health and MedicineC. Positron Emission Tomography

  36. Nuclear Fission Nuclear fission is the splitting apart of a heavy nucleus into lighter nuclei and neutrons. It can begin when a neutron bombards a uranium-235 nucleus: 91 142 235 1 1 n n + + + Kr Ba 3 U 36 56 92 0 0 • The bombarded U-235 nucleus splits apart into krypton-91, barium-142, and three high-energy neutrons, while releasing a great deal of energy.

  37. Nuclear Fission and Nuclear FusionA. Nuclear Fission • The released neutrons can then bombard other uranium nuclei, creating a chain reaction. • Critical mass: The minimum amount of U-235 needed to sustain a chain reaction.

  38. Nuclear Fission

  39. Nuclear Fission • A nuclear power plant uses the large amount of energy released in fission. • This energy is used to boil water and create steam, which turns a turbine and generates electricity. • The dangers of generating nuclear power are possible radiation leaks and the disposal of nuclear waste. • Radiation leaks can be minimized by containment facilities within the power plant itself. • Nuclear waste is currently buried, but it is unclear whether this is the best method.

  40. Nuclear Power Plant

  41. Nuclear Fusion Nuclear fusion is the joining together of two light nuclei to form a larger nucleus. • Hydrogen-2 (deuterium) and hydrogen-3 (tritium) undergo fusion to create a helium nucleus: 3 2 4 1 H H He n + + 1 1 2 0 • A neutron and a large amount of energy are also produced. Fusion is not currently useable as an energy source because it can only occur at extremely high temperatures and pressures.

  42. Decay Series for U-238 β, γ α β, γ 6.7 hrs 4.5 x 109 yr 25 days α 2.5 x 105 yr α α,γ 2.3 x 103 yr α,γ 8 x 104 yr 4 days α 3 min α 1.6 x 10-4 sec β, γ 20 min β, γ 27 min β, γ 22 yr α 138 days β 5 days

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