Chapters 3 & 22 Kishan Alluri Christina Costeas Sandy Jiang Patrick Morgan Ben Wong http://www.youtube.com/watch?v=XU8nMKk zbT8 Born in Manchester, England in December 1856 Studied physics and mathematics Won a nobel prize in 1906 1. 2. 3. 4. An object placed between the cathode and the opposite end of the tube cast a shadow on the glass. A paddle wheel placed on rails between the electrodes rolled along the rails from the cathode toward the anode. Cathode rays were deflected by a magnetic field in the same manner as a wire carrying electric current, which was known to have a negative charge. The rays were deflected away from a negatively charged object. Experiments supported hypothesis that the particles that compose cathode rays are negatively charged Measured the ratio of cathode-ray particles to their mass—found it was always the same Concluded that all cathode rays are composed of identical negatively charged particles called electrons Experiments revealed the electron has a very large charge for its tiny mass By: Katrina Leung, Jesse Stathis, Jenna Taormina, Danielle Zhang, Matt Odea Electrons are really small Mass of electron 1/2000 the mass of a hydrogen atom Electron has a mass of 9.109 * 10^-31kg or 1/1837 the mass of a hydrogen atom Electrons carry a negative charge http://www.youtube.com/watch?v=XMfYHag7Liw 1. 2. Because atoms are electrically neutral, they must contain a positive charge to balance the negative electrons. Because electrons have so much less mass than atoms, atoms must contain other particles that account for most of their mass. As flawlessly explained by: Adam, Jane, Justin, Jeremy, rob Born 1871 in New Zealand In early work, discovered radioactive half-life Had an element named after himrutherfordium Became known as the father of nuclear physics Assistants Geiger and Marsden bombarded a thin piece of gold foil with a narrow beam of alpha particles. Some of the particles were redirected by the gold foil back towards their source. Rutherford thus concluded that the force must be caused by a very densely packed bundle of matter with a positive charge, which he called the nucleus. Rutherford had discovered that the volume of the nucleus was very small compared to the total volume of the atom, suggesting that there was a lot of empty space. By Monica, Santosh, Jennie, Antonella, and Drew In 1932, Chadwick discovered a previously unknown particle in the atomic nucleus.3 This particle became known as the neutron because of its lack of electric charge. Chadwick's discovery was crucial for the fission of uranium 235. mass # = protons + neutrons always a whole number NOT on the Periodic Table! © Addison-Wesley Publishing Company, Inc. Atoms of the same element with different mass numbers. Nuclear symbol: Mass # Atomic # 12 6 Hyphen notation: carbon-12 C © Addison-Wesley Publishing Company, Inc. Chlorine-37 ◦ atomic #: 17 ◦ mass #: 37 ◦ # of protons:17 ◦ # of electrons:17 ◦ # of neutrons:20 37 17 Cl Chlorine-35 ◦ atomic #: 17 ◦ mass #: 35 ◦ # of protons:17 ◦ # of electrons:17 ◦ # of neutrons:18 35 17 Cl 12C atom = 1.992 × 10-23 g atomic mass unit (amu) 1 amu = 1/12 the mass of a 12C atom 1 p = 1.007276 amu 1 n = 1.008665 amu 1 e- = 0.0005486 amu C. Johannesson © Addison-Wesley Publishing Company, Inc. weighted average of all isotopes on the Periodic Table round to 2 decimal places Avg. Atomic Mass (mass)(% ) (mass)(% ) 100 EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% 16O, 0.04% 17O, and 0.20% 18O. Avg. (16)(99.76 ) (17)(0.04) (18)(0.20) 16.00 Atomic 100 amu Mass EX: Find chlorine’s average atomic mass if approximately 8 of every 10 atoms are chlorine-35 and 2 are chlorine-37. Avg. Atomic Mass (35)(8) (37)(2) 35.40 amu 100 Atom = nuclide Nucleus = nucleon Difference between the mass of an atom and the mass of its individual particles. 4.00260 amu 4.03298 amu Protons - 1.007276 u Electrons – 0.0005486 u Neutrons – 1.008665 u Ex. Helium-4 has an atomic mass of 4.002602 Calculate the mass defect: 2 Protons = (2x1.007276)= 2.014552u 2 Electrons = (2x0.0005486) = 0.001097u 2 Neutrons = (2x1.008665)= 2.017330u Total = 4.032979 u Mass defect = 4.032979 - 4.002602= 0.030377 It is nuclear binding: (Energy released when a nucleus is formed from nucleons) According to E=mc2: ◦ Mass can be converted into energy and energy to mass The mass defect is caused by the conversion of mass to energy upon formation of the nucleus. E=mc2 ◦ ◦ ◦ E-energy (J, Joules) m- mass (kg) c- speed of light (3.00x108 m/s) J= kg x m2 s2 Steps: 1. Calculate the mass defect in (u). 2. Convert to kg using 1u=1.6605X10-27kg 3. Plug in to energy equation ◦ 1. Calculate the binding energy of Sulfur-32. The measured atomic mass is 31.972070 u. (4.36 x 10-11 J) 2. Calculate the nuclear binding energy per mole of Oxygen-16. The measured atomic mass of oxygen is 15.994915u. (1.23 x 1013 J) 3. Calculate the binding energy per nucleon of a Manganese-55 atom. It’s measured atomic mass is 54.938047 u. (1.41 x 10-12J) Energy released when a nucleus is formed from nucleons. High binding energy = stable nucleus. E= 2 mc E: energy (J) m: mass defect (kg) c: speed of light (3.00×108 m/s) Calculate the binding energies of the following two nuclei, and indicate which nucleus releases more energy when formed. A. Potassium–35, Atomic mass 34.988011 B. Sodium – 23, Atomic Mass 22.989767 A. Potassium–35, Atomic mass 34.988011 4.47 X 10-11 J B. Sodium – 23, Atomic Mass 22.989767 2.99 x 10 -11J Potassium releases more energy Unstable nuclides are radioactive and undergo radioactive decay. - Binding energy per nucleon, is the binding energy of the nucleus divided by its number of nucleons. - The higher the binding energy per nucleon, the more tightly the nucleons are held together. - Elements with intermediate atomic masses have the greatest binding energies per nucleon and are therefore the most stable. What observations can you make? Atoms having low atomic numbers, are the most stable. ◦ N:P = 1:1 As atomic number increases the N:P increases (1.5:1) Why does this happen? - Explained by the relationship btwn nuclear force and electrostatic forces btwn protons. Protons in the nucleus repel all other protons through electrostatic repulsion. As #p increase, the repulsive electrostatic force between protons increase faster than the nuclear force More neutrons are required to increase the nuclear force to stabilize the nucleus. Beyond Bismuth (#83), the repulsive forces of protons are so great that no stable nuclide exists. Stable nuclei tend to have even number of nucleons Alpha particle () ◦ helium nucleus ◦ 2 protons and 2 neutrons bound together and emitted from the nucleus ◦ Restricted nearly to heavy atomic nuclei ◦ Mostly because protons numbers need to be reduced to stabilize the nuclei Beta (-) ◦ Is an electron emitted from the nucleus during some kinds of radioactive decay. ◦ Usually for the nuclides above the band of stability, to decrease the number of neutrons. ◦ Electron is emitted from the nucleus as a beta particle. Positron particle (+) ◦ Particle has the same mass as an electron but has a positive charge and emitted from the nucleus ◦ Proton is converted into a neutron Alpha particle () ◦ helium nucleus Beta particle (-) electron Positron (+) positron 4 2 He 0 -1 e 0 1 e Gamma () high-energy photon 2+ 11+ 0 Alpha Emission 238 92 parent nuclide U Th He 234 90 daughter nuclide 4 2 alpha particle Numbers must balance!! Beta Emission 131 53 I Xe e 131 54 0 -1 electron Positron Emission 38 19 K Ar e 38 18 0 1 positron Electron Capture 106 47 Ag e 0 -1 106 46 Pd electron Gamma Emission Usually follows other types of decay. Transmutation One element becomes another. 238 92 U 234 90 I 131 54 131 53 38 19 106 47 Th He 4 2 Xe e 0 -1 K Ar e 38 18 Ag e 0 -1 0 1 106 46 Pd 238 92 U 234 90 I 131 54 131 53 38 19 106 47 Th He 4 2 Xe e 0 -1 K Ar e 38 18 Ag e 0 -1 0 1 106 46 Pd 238 92 U 234 90 I 131 54 131 53 38 19 106 47 Th He 4 2 Xe e 0 -1 K Ar e 38 18 Ag e 0 -1 0 1 106 46 Pd 238 92 U 234 90 I 131 54 131 53 38 19 106 47 Th He 4 2 Xe e 0 -1 K Ar e 38 18 Ag e 0 -1 0 1 106 46 Pd 238 92 U 234 90 I 131 54 131 53 38 19 106 47 Th He 4 2 Xe e 0 -1 K Ar e 38 18 Ag e 0 -1 0 1 106 46 Pd Why nuclides decay… ◦ need stable ratio of neutrons to protons DECAY SERIES TRANSPARENCY When number of protons is plotted against number of neutrons, a belt-like graph is obtained. Atoms of low atomic numbers have stable nuclei with a ratio of 1:1, p:n As atomic number increases, the p:n increases Explained by nuclear and electrostatic forces between protons. ◦ Protons in the nucleus repel each other bc of electrostatic repulsion ◦ However Nuclear forces allow protons to attract to other protons in close proximity As #p increase the repulsive electrostatic force between protons increase faster than the nuclear force. Therefore creating an unstable nucleus. ◦ More neutrons are required to stabilize this force. The spontaneous disintegration of a nucleus into a slightly lighter nucleus, accompanied by the emission of particles, electromagnetic radiation or both. Leads to more stable nucleons. Half-life (t½) ◦ Time required for half the atoms of a radioactive nuclide to decay. ◦ Shorter half-life = less stable. mf m ( ) 1 n i 2 mf: mi: n: n: final mass initial mass # of half-lives t/T t = time elapsed T = Length of 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 mf = mi (½)n mi = 25 g mf = (25 g)(0.5)12 mf = ? mf = 0.0061 g total time = 60.0 s n = 60.0s ÷ 5.0s The half-life of carbon-14 is 5715 years. How long will it be until only half of the carbon-14 in a sample remains? (5715y) The EPA is concerned about the levels of radon gas in homes. The half-life of radon222 isotope is 3.8days. If a sample of gas taken from a basement contained 4.38ug of radon-222, how much will remain after 15.2 days? (0.274ug) Uranium-238 decays through alpha decay with a half life of 4.46x109years. How long would it take for 7/8 of a sample of uranium238 to decay? (three half-lives or 1.34 x 1010 years) Parent Nuclide: The heaviest nuclide of each decay series Daughter Nuclide: The nuclide produced by decay of the parent nuclide splitting a nucleus into two or more smaller nuclei 1 g of 235U = 3 tons of coal 235 92 U chain reaction - self-propagating reaction critical mass mass required to sustain a chain reaction 2 1 combining of two nuclei to form one nucleus of larger mass thermonuclear reaction – requires temp of 40,000,000 K to sustain 1 g of fusion fuel = 20 tons of coal occurs naturally in stars H H 3 1 FISSION 235U is limited danger of meltdown toxic waste thermal pollution FUSION fuel is abundant no danger of meltdown no toxic waste not yet sustainable Fission Reactors Cooling Tower Fission Reactors Fusion Reactors (not yet sustainable) Fusion Reactors (not yet sustainable) National Spherical Torus Experiment Tokamak Fusion Test Reactor Princeton University Transuranium Elements ◦ elements with atomic #s above 92 ◦ synthetically produced in nuclear reactors and accelerators ◦ most decay very rapidly 238 92 U He Pu 4 2 242 94 half-life measurements of radioactive elements are used to determine the age of an object decay rate indicates amount of radioactive material EX: 14C - up to 40,000 years 238U and 40K - over 300,000 years Radioisotope Tracers ◦ absorbed by specific organs and used to diagnose diseases Radiation Treatment ◦ larger doses are used to kill cancerous cells in targeted organs ◦ internal or external radiation source Radiation treatment using -rays from cobalt60. 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 Food Irradiation ◦ radiation is used to kill bacteria Radioactive Tracers ◦ explore chemical pathways ◦ trace water flow ◦ study plant growth, photosynthesis Consumer Products ◦ ionizing smoke detectors - 241Am