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NUCLEAR CHEMISTRY 1 Nuclear Chemistry At the conclusion of our time together, you should be able to: 1. List 4 people who contributed to the discovery of radiation and their contribution 2. List the subatomic parts of the atom including quarks 3. Explain the difference in isotopes of an atom 4. Explain alpha, beta, and gamma radiation and what happens to the nucleus 5. Calculate half-lives of radioactive materials 6. List differences between a fusion and fission reactions 2 3 Interesting Signs: Nuclear Chemistry At the conclusion of our time together, you should be able to: 1. List 4 people who contributed to the discovery of radiation and their contribution 4 The People Behind the Discovery of Radiation 5 Roentgen (1895) •Studied fluorescent materials that glowed when hit with a beam of electrons. •Discovered a mysterious form of radiation was given off even without electron beam. This radiation could pass through paper and other objects but not dense materials (lead, bone). •Called them X-rays 6 Becquerel (1896) •Studied fluorescent minerals containing uranium. •Discovered radioactivity by accident on a cloudy day: •Thought that an external source was needed to produce the mysterious radiation. •Found that uranium emits radiation without external source. 7 8 All You Really Need To Know You Can Learn From Noah's Ark 7. For safety's sake, travel in pairs. 8. Two heads are better than one. Pierre and Marie Curie Thought radioactivity was a property of heavy elements. During study, discovered new radioactive elements: Polonium and Radium. Wondered how a small mass can give off a large amount of energy: Explained by Einstein with E=mc2. 9 Mass Defect • Difference between the mass of an atom and the mass of its individual particles. 4.00260 amu 4.03298 amu 10 Mass Defect • Some of the mass can be converted into energy • Shown by a very famous equation! E=mc2 Energy Mass Speed of light 11 Nuclear Binding Energy • Energy released when a nucleus is formed from nucleons. • High binding energy = stable nucleus. E = mc2 E: energy (J) m: mass defect (kg) c: speed of light (3.00×108 m/s) 12 Nuclear Binding Energy Unstable nuclides are radioactive and undergo radioactive decay. 13 14 Rutherford •Studied radioactivity and named types of nuclear radiation. •Discovered that elements decay into other elements after emitting nuclear radiation. Called it Nuclear Decay. •Gold foil experiment revealed that the mass of an atom is concentrated in the nucleus (atom is mostly space) 15 Radiation So let’s see if you can: 1. List 4 people who contributed to the discovery of radiation and their contribution 16 Review of the Atom and Isotopes 17 Review of Atoms and Isotopes At the conclusion of our time together, you should be able to: 1. List the subatomic parts of the atom including quarks 2. Explain the difference in isotopes of an atom 18 19 Euphemisms in Science We all know that some politicians and government spokesmen use certain euphemistic phrases to give an aura of respectability to descriptions of events or actions which would be offensive when expressed in plain English. The following is a list of Euphemisms in Science and their translations into plain English. “It is clear that much additional work will be required before a complete understanding...” I don't understand this at all! The Atom • An atom is the smallest particle of an element that has the chemical properties of the element. • The atom is extremely small. One teaspoon of water has 3 times as many atoms as the Atlantic Ocean has teaspoons of water. • If a large sports stadium were an atom, a marble on the 50 yard line would represent the nucleus. 20 21 The Atom An atom consists of a • nucleus – (of protons and neutrons) • electrons in space about the nucleus. Electron Cloud Nucleus ATOMIC COMPOSITION • Protons (p+) – + electrical charge – mass = 1.672623 x 10-24 g – relative mass = 1.007 atomic mass units (amu) but we can round to 1 22 ATOMIC COMPOSITION • Electrons (e-) – negative electrical charge – relative mass = 0.0005 amu – but we can round to 0 • Neutrons (no) – no electrical charge – mass = 1.009 amu – but we can round to 1 23 Mass Comparison 24 Proton is about 2000 x electron Electron is about 1,000,000 x photon -1 e . Proton Electron Photon Familiar Saying Eschew the implement of correction and vitiate the scion. Spare the rod, spoil the child! 25 26 Atomic Number, Z All atoms of the same element have the same number of protons in the nucleus, Z 13 Al 26.981 Atomic Number Atomic Symbol Average Atomic Mass 27 Mass Number, A • C atom with 6 protons and 6 neutrons is the mass standard • = 12 atomic mass units (amu) • Mass Number (A) = # protons + # neutrons • NOT on the periodic table • It is the Average atomic mass (which is on the periodic table) rounded to the nearest whole number 28 In Summary • Atomic number = the # protons and also the # electrons • Mass Number = average atomic number rounded to the nearest whole number • Mass Number = # protons + # neutrons Remember Isotopes?? 1H 2H 3H 29 30 Isotopes Atoms of the same element (same number of protons) with a different number of neutrons. 1H 2H 3H 31 Isotopes 12C 13C 6 Protons 6 Protons 6 Neutrons 7 Neutrons 32 Isotopes Therefore: The Average Atomic Mass will be some fraction between all the mass numbers of all the isotopes of that element! For Hydrogen, since most of the isotopes of are in the left form, the average atomic mass is slightly more than 1 amu. 1H 2H 3H 33 To: Santa Re: Where Are My Gifts?! Actual E-mails to EmailSanta.com • I’m sorry for putting all that Ex-lax in your milk last year, but I wasn’t sure if you were real. • My dad was really mad. • Bri, 7 34 Tevatron - world's highest-energy particle accelerator. Four miles in circumference Particles go around at 99.9999% of the speed of light. 35 Particle accelerator 36 We send protons and antiprotons in opposite directions, and smash them together. 37 We’ve Discovered Other Particles Matter anti-Matter Example: electron positron e-1 e+1 38 We’ve Discovered Other Particles Matter anti-Matter Example: Proton +1 P anti-Proton -1 P 39 We’ve Discovered Other Particles Quarks Up 2 3 Leptons electron e-1 Down -1 3 40 41 Sub-Subatomic Particles • Quarks • Sum of the charges is the electrical charge • Fast moving points of energy Up quark = + 2/3 Down quark = - 1/3 He 42 Structure of Sub-Subatomic Particles Quark Calculations of Charges Each proton is 2 up quarks and 1 down quark 2(2/3) – 1(1/3) = 4/3 – 1/3 = 3/3 or +1 Each neutron is 2 down quarks and 1 up quark 2(-1/3) + 2/3 = 0 Each electron is composed of 3 down quarks 3(-1/3) = -1 43 A.P. TEST IN ADVANCED BIOLOGY • • You have been provided with a razor blade, a piece of gauze, needle and thread and a bottle of scotch. Remove your appendix. Do not suture your work until it has been inspected. You have 15 minutes. Review of Atoms and Isotopes Let’s see if you can: 1. List the subatomic parts of the atom including quarks 2. Explain the difference in isotopes of an atom 44 45 Self-Check Isotope Mo-101 H-2 C-14 U-238 Bi-210 He-4 Symbol 101 42 2 1 14 6 238 92 210 83 4 2 Mo H C U Bi He # protons # neutrons Atomic Mass 42 59 101 1 1 2 6 8 14 92 146 238 83 127 210 2 2 4 46 Proton Mass Charge Neutron Electron 1 amu 1 amu 0 amu +1 0 -1 47 What is d Made of 3 Quarks 1 up 2 down u Neutron d 48 What is u Made of 3 Quarks 2 up 1 down d Proton u Bill Gates' Rules Here is a list of 11 things that many high school and college graduates did not learn in school. In his book, Bill Gates talks about how feel-good, politically-correct teachings created a full generation of kids with no concept of reality and how this concept has set them up for failure in the real world. RULE 4 If you think your teacher is tough, wait till you get a boss. He doesn't have tenure. 49 Nuclear Reactions and Half-Life At the conclusion of our time together, you should be able to: 1. Explain alpha, beta, and gamma radiation and what happens to the nucleus 2. Balance 5 different types of nuclear reactions 3. Calculate half-lives of radioactive materials 50 Nuclear Reactions vs. Normal Chemical Changes • Nuclear reactions involve the nucleus • The nucleus opens, and protons and neutrons are rearranged • The opening of the nucleus releases a tremendous amount of energy that holds the nucleus together – called what? • Binding energy • “Normal” Chemical Reactions involve electrons, not protons and neutrons 51 52 Types of Radiation • Alpha (ά) – a positively charged helium isotope - we usually ignore the charge because it involves electrons, not protons and neutrons 4 2 He •Beta (β) – an electron 0 1 •Gamma (γ) – pure energy; called a ray rather than a particle 0 0 e 53 Other Nuclear Particles • Neutron 1 0 • Positron – a positive electron 0 1 •Proton – usually referred to as hydrogen-1 1 1 •Any other elemental isotope n e H 54 Chemical Compound Quiz Sodium hydrogen carbonate gives a nice lift to biscuits. What is the common name? Baking Powder 55 Penetrating Ability of Radiation Radioactivity Positron emission 56 Radioactive Particles And Rays Alpha Particle 2 Protons 2 Neutrons 57 58 Radioactive decay Radioactivity Change in the nucleus of an atom Loss of an Alpha, Beta, or Gamma particle 3 Forms of Radioactive Decay Alpha emission Changes Atomic Mass 2P 2N Beta emission Neutron turns into a Proton electron Gamma emission light 59 Balancing Nuclear Reactions •In the reactants (starting materials – on the left side of an equation) and products (final products – on the right side of an equation) Atomic numbers must balance and Mass numbers must balance •Use a particle or isotope to fill in the missing protons and neutrons 60 61 15 Helpful Hints On The Lab Report from Mr. T’s Vast Lab Experience!!! Hint #15. When your calculated answers don't match the answer you should have gotten utilize the TF2 constant. TF2 constant (Toburen Fudge Factor): that quantity which, when multiplied by, divided by, added to or subtracted from the answer you got, gives you the answer you should have gotten. 62 Alpha Emission occurs when the nucleus has too many protons which cause excessive repulsion. 238 234 92 90 U parent nuclide Th He daughter nuclide 4 2 alpha particle Numbers must balance!! 63 Alpha Emission Ex. Plutonium-239 undergoes alpha decay 239 94 Atomic Mass: Atomic #: 235 92 Pu U + 4 2 He 239 = 235 + 4 94 = 92 + 2 Masses must be equal = Conservation of mass 64 Beta Emission occurs when the neutron to proton ratio is too great. 131 53 I 131 54 Xe e 0 -1 electron 65 Remember Quark Charges Beta Emission Means a Neutron becomes a Proton Each electron is composed of 3 down quarks 3(-1/3) = -1 (Lost) Each neutron is 2 down quarks and 1 up quark 2(-1/3) + 2/3 = 0 - 3(-1/3) = +1 Neutron becomes a proton Therefore, mass number stays the same but atomic number goes up one! Neutron to Proton 66 67 Beta Emission Ex. Polonium-210 undergoes beta decay to produce this daughter nuclide 210 84 Atomic Mass: Po 210 - 210 Atomic #: A Z 0 = = 1 = = 84 84 A Z + X = X + A A 0 + -1 = 210 Z + Z = 210 85 At 85 0 -1 e 68 Positron Emission Occurs when the neutron to proton ratio is too small. 38 19 K Ar e 38 18 0 1 positron 69 Positron Emission Ex. Polonium-210 undergoes positron emission to produce this daughter nuclide 210 84 Atomic Mass: Po 210 - 210 Atomic #: A Z 0 = = 1 = = 84 84 A Z - X = X + A A 0 + 1 = 210 Z + Z = 210 83 Bi 83 0 +1 e Electron Capture 70 occurs when the neutron to proton ratio in the nucleus is too small. 106 47 Ag e 0 -1 106 46 Pd electron Electron Capture Ex. Polonium-210 captures an electron to produce this daughter nuclide 210 84 Po Atomic Mass: 0 + -1 210 A Z e + 0 A Atomic #: 84 + -1 Z A Z X = = = = = A 210 Z 83 210 83 Bi X 71 Murphy's Laws of Science and Technology A meeting is an event in which minutes are kept and the hours are lost. 72 Gamma Emission occurs when the nucleus is at too high an energy. Emission of high energy electromagnetic wave. 73 74 75 Gamma Emission Ex. Polonium-210 undergoes gamma decay to produce this daughter nuclide 210 84 Atomic Mass: Atomic #: A Z Po A = = Z = = 210 84 A Z X = X + 0 0 A + 0 Z + 0 210 84 210 84 Po 76 Now Lets’ Consider Nuclear Decay and Half-Life Band of Stability and Radioactive Decay 77 Nuclear Decay • Why nuclides decay – need stable ratio of neutrons to protons •Transmutation-One element becomes another. 238 92 U I 131 54 K 38 18 131 53 38 19 106 47 Th He 234 90 4 2 Xe -10 e Ar Ag e 0 -1 0 1 106 46 e Pd More than 83 protons means that the nuclei is unstable (radioactive) 78 Half-life • Half-life (t½) – Time required for half the atoms of a radioactive nuclide to decay. – Shorter half-life = less stable. 79 Half-life mf m ( ) 1 n i 2 mf: mi: n: final mass initial mass # of half-lives 80 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: WORK: t½ = 5.0 s mi = 25 g mf = ? total time = 60.0 s n = 60.0s ÷ 5.0s =12 mf = mi (½)n mf = (25 g)(0.5)12 mf = 0.0061 g 81 Interesting Signs: Nuclear Reactions and Half-Life Let’s see if you can: 1. Explain alpha, beta, and gamma radiation and what happens to the nucleus 2. Balance 5 different types of nuclear reactions 3. Calculate half-lives of radioactive materials 82 83 Penetrating Ability Types of Radiation? • Alpha particle () – helium nucleus 84 Charge Shielding 4 2 He 2+ • Beta particle (-) – electron 0 -1 1- • Positron (+) – positron 0 1 • Gamma () – high-energy photon 0 0 e e paper lead 1+ 0 concrete 85 Alpha Emission Ex. Polonium-210 undergoes alpha decay to produce this daughter nuclide 210 84 Atomic Mass: Po 210 - 210 Atomic #: A Z 4 = = 2 = = 84 84 A Z - X = + A A + X = 206 Z + Z = 206 82 Pb 82 4 2 4 2 He Remember in Nuclear Reactions • Alpha emission Note that mass number (A) goes down by 4 and atomic number (Z) goes down by 2. Nucleons (nuclear particles… protons and neutrons) are rearranged but conserved 86 Remember in Nuclear Reactions • Beta emission Note that mass number (A) is unchanged and atomic number (Z) goes up by 1. 87 Remember the Other Types of Nuclear Reactions Positron (0+1): a positive electron 207 Electron capture: the capture of an electron 207 88 89 The “Y” Generation!!! 90 Learning Check What radioactive isotope is produced in the following bombardment of boron? 10B 5 + 4He ? + 2 1n 0 13Li 7 91 Write Nuclear Equations! Write the nuclear equation for the beta emitter Co-60. 60Co 27 - 0e -1 60Ni 28 92 What is Half-Life? • HALF-LIFE is the time that it takes for 1/2 a sample to decompose. • The rate of a nuclear transformation depends only on the “reactant” concentration. 93 Half-Life Decay of 20.0 mg of 15O. What remains after 3 half-lives? After 5 half-lives? Kinetics of Radioactive Decay For each duration (half-life), one half of the substance decomposes. For example: Ra-234 has a half-life of 3.6 days If you start with 50 grams of Ra-234 After 3.6 days > 25 grams After 7.2 days > 12.5 grams After 10.8 days > 6.25 grams 94 95 Learning Check! The half life of I-123 is 13 hr. How much of a 64 mg sample of I-123 is left after 39 hours? mf m ( ) 1 n i 2 X mg = 64 (1/2)3 8.0 mg 96 Another Interesting Sign: Radiation At the conclusion of our time together, you should be able to: 1. List differences between a fusion and fission reactions 97 Nuclear Fission 98 Nuclear Fission Fission is the splitting of atoms These are usually very large, so that they are not as stable Fission chain has three general steps: 1. Initiation. Reaction of a single atom starts the chain (e.g., 235U + neutron) 2. Propagation. 236U fission releases neutrons that initiate other fissions 3. ___________ . 99 Representation Of A Fission Process. 100 Nuclear Fission & POWER • Currently about 103 nuclear power plants in the U.S. and about 435 worldwide. • 17% of the world’s energy comes from nuclear. 101 Diagram Of A Nuclear Power Plant. 102 103 Nuclear Fusion Fusion small nuclei combine 2H 1 + 3H 4He 1 2 + 1n + 0 Occurs in the sun and other stars Energy 104 Nuclear Fusion Fusion • Excessive heat can not be contained • Attempts at “cold” fusion have FAILED. • “Hot” fusion is difficult to contain 105 Geiger Counter • Used to detect radioactive substances 106 Effects of Radiation 107 108 When I was a kid… • We didn’t have padding under our jungle gyms. We had rocks! • We didn’t have safety belts on our swing sets. The whole goal was to get as high as you could and then launch yourself. • We rode our bikes without helmets. • No sunscreen, just suntan lotion, and got burned to a crisp. 109 When I was a kid… • • • • We played with BB guns. Ran with scissors. Blew up Barbie dolls with M-80’s. Wore Halloween costumes with asbestos. • But for safety…. • our moms made us wait an hour after we ate before we went swimming!!!! Radiocarbon Dating Radioactive C-14 is formed in the upper atmosphere by nuclear reactions initiated by neutrons in cosmic radiation 14N + 1 n ---> 14C + 1H o The C-14 is oxidized to CO2, which circulates through the biosphere. When a plant dies, the C-14 is not replenished. But the C-14 continues to decay with t1/2 = 5730 years. Activity of a sample can be used to date the sample. 110 Artificial Nuclear Reactions New elements or new isotopes of known elements are produced by bombarding an atom with a subatomic particle such as a proton or neutron -- or even a much heavier particle such as 4He and 11B. Reactions using neutrons are called reactions because a ray is usually emitted. Radioisotopes used in medicine are often made by reactions. 111 Artificial Nuclear Reactions Example of a reaction is production of radioactive 31P for use in studies of P uptake in the body. 31 15P + 0n 1 32 P 15 + 112 Transuranium Elements Elements beyond 92 (transuranium) made starting with an reaction 238 U 92 + 239 U 92 239 93Np 1 0n + 239 92U 239 0 Np + 93 -1 239 94Pu + 0 -1 113 Nuclear Medicine: Imaging Thyroid imaging using Tc-99m 114 115 Food Irradiation •Food can be irradiated with rays from 60Co or 137Cs. •Irradiated milk has a shelf life of 3 months without refrigeration. •USDA has approved irradiation of meats and eggs. 116 Fission or Fusion?? Familiar Saying One pyrus malus per diem restrains the arrival of the Hippocratic apostle. An apple a day keeps the doctor away!! 117 118