Module 1 Unit 2 Enggchem Nuclear Chemistry and Energy PDF

Unit 2 Nuclear Chemistry and Energy UNIT LEARNING OUTCOMES TLO 2: Demonstrate appropriate concepts of Nuclear Chemistry and Energy. ENGAGE Nuclear energy, also called atomic...

Unit 2 Nuclear Chemistry and Energy UNIT LEARNING OUTCOMES TLO 2: Demonstrate appropriate concepts of Nuclear Chemistry and Energy. ENGAGE Nuclear energy, also called atomic energy, energy that is released in significant amounts in processes that affect atomic nuclei, the dense cores of atoms. It is distinct from the energy of other atomic phenomena such as ordinary chemical reactions, which involve only the orbital electrons of atoms. One method of releasing nuclear energy is by controlled nuclear fission in devices called reactors, which now operate in many parts of the world for the production of electricity. Another method for obtaining nuclear energy, controlled nuclear fusion, holds promise but has not been perfected by 2020. Nuclear energy has been released explosively by both nuclear fusion and nuclear fission. One notable application of nuclear energy is through nuclear power plants. Nuclear power is a clean and efficient way of boiling water to make steam, which turns turbines to produce electricity. Nuclear power plants use low-enriched uranium fuel to produce electricity through a process called fission—the splitting of uranium atoms in a nuclear reactor. Uranium fuel consists of small, hard ceramic pellets that are packaged into long, vertical tubes. Bundles of this fuel are inserted into the reactor.  To get a quick overview of what nuclear chemistry and energy, watch this video entitled ― Nuclear Chemistry: Crash Course Chemistry #38 ‖ using the link https://www.youtube.com/watch?v=KWAsz59F8gA. EXPLORE Radioactivity It is a phenomenon that occurs in a number of substances. Atoms of the substances spontaneously emit invisible but energetic radiations, which can penetrate materials that are opaque to visible light. The effects of these radiations can be harmful to living cells but, when used the right way, they have wide range of beneficial applications. History of Radiation: The Birth of Atomic Models At the end pf the 19yh century, many scientists did not realize they were on the edge of a revolution in physics… “The most important fundamental laws and facts of physical science have all been discovered, and these are now so firmly established that the possibility of their ever being supplanted in consequence of new discoveries is exceedingly remote… Our future must be looked for in the sixth place of the decimals.” - Albert Michelson, 1984 Prepared by: Engr. N. L. Escalante 22 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  Radiation Chronicle ▪ 400 B.C. - In Greece, Democritus proclaims all material things are made of tiny particles ―atoms‖, or ―not divisible‖ ▪ 1789 - The element uranium was discovered by Martin Klaproth ▪ 1869 - Dmitri Mendeleyev developed the periodic law of elements, which later evolved in the Table of Elements ▪ 1885 - Balmer publishes an empirical formula that gives the observed wavelength of hydrogen light spectra. 1 1 1  R  2  2   2 n  ▪ 1890 - Thorium is first used in mantles for camping lanterns ▪ 1895 - Wilhelm Roentgen discovered X-rays on 8th November 1895; the World immediately realizes its medical potential and he won the Novel Prize in 1901 ▪ 1896 - Henri Becquerel discovered radioactivity on 26 February 1896 and shared the Nobel Prize with P. Curie ―Some atoms give off energy in form of ways. Uranium gives off radiation.‖ - Henri Becquerel ▪ 1897 - J.J. Thomson discovers the electron ▪ 1898 - Marie and Pierre Curie discovered the first radioactive elements: radium and polonium; radioactivity is named by Marie Curie; Marie won the Nobel Prize in 1911 for discovery of radium and polonium ▪ 1899 - Ernest Rutherford concludes that radiation can be divided into two types: alpha and beta rays; won the Nobel Prize in 1908 ▪ 1900 - Pierre Curie observes another type of radiation - the gamma rays; shared the Nobel Prize in 1903 with Becquerel ▪ 1905 - Albert Einstein develops the theory about relationship between mass and energy: E = mc2; won Nobel Prize in 1919 for discovery of photoeffect ▪ 1911 - Ernest Rutherford discovers that most of an atom is empty space and indetifies the atomic nucleus ▪ 1911 - George de Hevesy conceives the idea of using radio tracers - applied later to medical diagnosis; won a Nobel Prize in 1943 ▪ 1913 - Niels Bohr introduces the first atom model, the mini solar system ▪ 1913 - Hans Geiger invents the Heiger counter form measuring radioactivity ▪ 1913 - Frederick Proesher publishes the first study on the intravenous injection of radium for therapy of various diseases ▪ 1920 - Ernest Rutherford discovered and named the proton ▪ 1927 - Herman Blumgart, A Boston physician, first uses radioactive tracers to diagnose heart disease ▪ 1932 - James Chadwick discovers the neutron; won Nobel Prize in 1935 ▪ 1932 - Ernest O. Lawrence and M. Stanlay Lovingston publish the first article on ―the production of high speed light ions without the use of high voltages‖ - a milestone on the production of usable quantities of radionucleids; E. Lawrence won Nobel Prize in 1939 for the cyclotron ▪ 1934 - Irene and Frederic Joliot-Curie discover artificial radioctivity; in 1935, Irene and Frederic Joliot-Curie received Nobel Prize for creating the first artificial radioactive isotope Prepared by: Engr. N. L. Escalante 23 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  ▪ 1935 - Nuclear medicine comes into existence when cyclotron-produced radioisotopes and nuclear radiation becomes available in the U.S. ▪ 1936 - John H. Lawrence, the brother of Ernest, makes the first clinical therapeutic application of an artificial radionucleid when he used phosphorous-32 to treat leukemia ▪ 1937 - John Livingoof and Glenn Seaborg discovered iron-59; in 1938, John Livingood and Glenn Seaborg discovered iodine-131 and cobalt-60 - all isotopes currently used in nuclear medicine; G Seaborg shared Nobel Prize with MacMillan in 1951 ▪ 1938 - Otto Hahn and Fritz Strassman, produce lighter elements by bombarding uranium with neutrons; Irene Joliot-Curie and Pavle Savich notice the same effect; however, it was Lise Meitner and Otto Frisch that recognized it as splitting of the atom - ―fission‖; O. Hahn won a Nobel Prize in 1944 ▪ 1938 - Enrico Fermi won a Nobel Prize for production of new elements by neutron radiation ▪ 1939 - The principles of a nuclear reactors was first recorded and sealed in an envelope where it remains secret during the WWII ▪ 1939 - Emilio Segre and Glenn Seaborg discovered technetium-99m - an isotope currently used in nuclear medicine ▪ 1939 - U.S. Advisory Committee on Uranium recommends a program to develop an atomic bomb (this is later named the Manhattan Project) ▪ 1940 - The Rockefeller Foundation funds the first cyclotron dedicated for biomedical radioisotope production at Washington University in St. Louis ▪ 1942 - The Manhattan Project is formed to secretly build the atomic bomb before the Nazis ▪ 1942 - Fermi demonstrated the first self-sustaining nuclear chain reaction in a lab at the University of Chicago ▪ 1942 - The United States drop atomic bombs on Hiroshima and Nagasaki. Japan surrenders First Reports of Injury ▪ Late 1896 Elihu Thomson - burns from deliberate exposure of a finger to X-rays ▪ Edison’s assistant - hair fell out & scalp became inflamed &ulcerated ▪ Mihran Kassabian (1870-1910) ▪ Sister Blandina (1871-1916)  In 1898, started work as radiographer in Cologne and held nervous patients & children with unprotected hands. She even controlled the degree of hardness of the X-ray tube by placing her hand behind of the screen. After 6 months, she suffered from strong flushing & swellings of hands and was diagnosed with an X-ray cancer. Some of her fingers were amputated and it worsened until her whole hand and arm were amputated.  In 1915, she suffered difficulties of breathing and her x-ray examination showed an extensive shadow on the left side of her thorax. She had also a large wound on her whole front- and back-side.  She died on 22nd October 1916. Prepared by: Engr. N. L. Escalante 24 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  First Radiotherapy Treatment ▪ Conducted by EMil Herman Grubbe on 29 January 1896 to a woman (50) with breast cancer ▪ The treatment consisted of 18 daily 1-hour irradiation ▪ The patient’s condition was relieved but she died shortly afterwards from metastases Radiation Protection ▪ Early Protective SUit include lead glasses, filters, tube shielding, early personal ―dosemasters‖, etc. ▪ 1898 - Roentgen Society of Inquiry ▪ 1915 - Roentgen Society publishes recommendations ▪ 1921 - British X-ray and Radiation Protection Committee established and issue reports ▪ 1928 - 2nd International Congress of Radiology adopts British recommendations + the Roentgen ▪ 1931 - USACXRP publishes the first recommendations (0.2 r/d) ▪ 4th ICR adopts 0.2 Roentgens per day limit Life Span Study ▪ About 94,000 persons, > 50% are still alive in 1995 ▪ By 1991, about 8,000 cancer deaths, ≈430 of these attributable to radiation ▪ 21 out of 800 in utero with dose > 10 mSv severely mentally retarded individuals have been identified ▪ No increase in hereditary disease Atomic Theory Part I: Rutherford - Birth of planetary model ▪ 1900: Alpha, beta, and gamma rays are known ▪ 1909: Rutherford conclude from bombarding thin gold foils with alpha particles (Po(214- 84))  Large angle deflection seen in 1/8000 alpha particles suggests the existence of a very small and massive nucleus  Proposed the planetary model ▪ We now know: ▪ Rnuc ≈ 1.3 A1/3 x 10-15 m ▪ Ratom ≈ 1.5 x 10-10 m Part II: Bohr’s hydrogen atom - 1913 ▪ Bohr was not satisfied from classical mechanics in the planetary model - unstable model since an accelerated charge will emit light and therefore lose energy ▪ Bohr postulates the first semi-classical model  Angular momentum of electron is quantized: mvr  nh  Then energy and orbital radii are also quantized: Prepared by: Engr. N. L. Escalante 25 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  0.529n 2  o  rn   A Z    13.6 Z 2 En  eV  n2 Problem with Bohr;s model and classical mechanics: ▪ Could only predict correctly the energy levels of H ▪ The dual behavior of light (particle and wave) could not be explained by classical mechanics ▪ The approach of Bohr of mixing classical mechanics and quantizing certain variables was suddenly heavily used  Other accurate predictions were made with new semi0classical or relativistic models  Prelude for Quantum Mechanics Birth of Quantum Mechanics: 1925 ▪ Simultaneously and independently:  Heizenberg actually realized that the reason Bohr’s model failed was that it was trying to predict none observable variables (position, speed)  Heizenberg actually created a model focusing on measurable variable - Balm wavelength:  Showed that Dp.Dx ≥ ħ or DE.Dt ≥ ħ  This is the Heizenberg uncertainty principle, stating that it is impossible to measure precisely the speed and location of a particle  Also showed that x.px was different from px.x. Others showed in this typical matrix property called Heizenberg model the Matrix Mechanics  Shroendiger established a law defined by a differential equation that describes matter as a wave (D2X and Dt)  Later, Schroendiger equation will be formalized by linear algebra and matrix simplification Nuclear Chemistry: Basics Nuclear Terminology ▪ Nuclide - atom with a specific number of protons in its nucleus  There are 27 stale nuclides in nature, others are radioactive ▪ Nucleon - proton or neutron, especially as part of an atomic nucleus ▪ Unstable isotope - naturally or artificially created isotope having an unstable nucleus that decays, emitting alpha, beta, or gamma rays until stability is reached ▪ Radionuclide - unstable isotope that undergoes nuclear decay  All isotopes of elements with ≥ 84 protons are radioactive; specific isotopes of lighter elements are also radioactive (e.g. 1 H ) 3 # nucleons = # protons + # neutrons Prepared by: Engr. N. L. Escalante 26 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  Chemical reaction: breal and form bonds between atoms but elements remain the same - nuclei are unchanged. Nuclear reactions differ from ordinary chemical reactions ▪ Atomic numbers of nuclei may change (elements are converted to other elements or an element can be converted to an isotope of that element) ▪ Protons, neutrons, electrons, and other elementary particles may be involved in a nuclear reaction ▪ Reactions occur between particles in nucleus ▪ Matter is converted to energy & huge amounts of energy are released ▪ Nuclear reactions involved a specific isotope of an element; different isotopes of an element may undergo different nuclear reactions We use a special notation to describe nuclear particles A Z X Z is the elemental symbol A is the mass number = total number of protons and neutrons in the nucleus Z is the atomic number = total number of protons in the nucleus - determines identity of element Examples: 12 6C Carbon with 6 neutrons (12 - 6 = 6 neutrons) 13 6C Carbon with 7 neutrons (13 - 6 = 7 neutrons) 235 92 U Uranium with 143 neutrons (235 - 92 = 143) 238 92 U Uranium with 146 neutrons (238 - 92 = 146)  Neutrons act as glue to hold the nucleus together ▪ For the smaller elements, the ratio of neutrons to protons is ~1:1 ▪ As the size of the nucleus increases, the ratio of neutrons to protons increases to ~2:1 Nuclear Stability ▪ An unstable isotope emits some kind of radiation, that is it is radioactive. ▪ A stable isotope is one that does not emit radiation, or, if it does its half-life is too long to have been measured. ▪ It is believed that the stability of the nucleus of an isotope is determined by the ratio of neutrons to protons. ▪ Observations of the atomic number of isotopes show us that:  Isotopes with atomic number (Z) > 82 are unstable  Of the elements with atomic number (Z) < 82, all have one or more stable isotopes except technetium (Z = 43) and promethium (Z = 61) which do not have any stable isotopes.  Isotopes with atomic number (Z) ≤ 20 and with a neutron (n) to proton (p) ratio of about 1 are more likely to be stable (n ÷ p ~ 1) Prepared by: Engr. N. L. Escalante 27 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  ▪ Observations on whether the nucleus contains odd or even numbers of protons and neutrons leads us to believe that a nucleus with:  odd numbers of protons and odd numbers of neutrons is most likely to be unstable  even number of protons and even numbers of neutrons is most likely to be stable ▪ Nuclei containing 2, 8, 20, 50, 82, or 126 protons or neutrons are generally more stable than nuclei that do not possess these magic numbers ▪ As the atomic number increases, more neutrons are needed to help bind the nucleus together, so there is a high neutron:proton ratio # protons # neutrons # stable nuclei Even Even 164 Even Odd 53 Odd Even 50 Odd Odd 4 Band of Stability Prepared by: Engr. N. L. Escalante 28 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  A nucleus is stable if it cannot be transformed into another configuration without adding energy from the outside. Of the thousands of nuclides that exist, about 250 are stable. A plot of the number of neutrons versus the number of protons for stable nuclei reveals that the stable isotopes fall into a narrow band. This region is known as the band of stability (also called the belt, zone, or valley of stability). The straight line in the figure above represents nuclei that have a 1:1 ratio of protons to neutrons (n:p ratio). Note that the lighter stable nuclei, in general, have equal numbers of protons and neutrons. For example, nitrogen-14 has seven protons and seven neutrons. Heavier stable nuclei, however, have increasingly more neutrons than protons. For example: iron-56 has 30 neutrons and 26 protons, an n:p ratio of 1.15, whereas the stable nuclide lead-207 has 125 neutrons and 82 protons, an n:p ratio equal to 1.52. This is because larger nuclei have more proton-proton repulsions, and require larger numbers of neutrons to provide compensating strong forces to overcome these electrostatic repulsions and hold the nucleus together. This plot shows the nuclides that are known to exist and those that are stable. The stable nuclides are indicated in blue, and the unstable nuclides are indicated in green. Note that all isotopes of elements with atomic numbers greater than 83 are unstable. The solid line is the line where n = Z.  Watch this video entitled ― Nuclear Stability ‖ using the link https://www.youtube.com/watch?v=H8Yd2T9MQBU to know the use of the diagram above.  Further discussions about Nuclear Stability can be found using this link https://www.ausetute.com.au/istability.html. Example Problems: 1. Which isotope in each of the following pairs should be more stable? a) 14 28 Si or 1429 Si b) 36 Li or 38 Li c) 11 23 Na or 11 20 Na 2. For each pair of elements listed, predict which one has more stable isotopes. a) Ni or Cu b) Se or Sb c) Cd or Au Solution: 1. Light elements (Z) ≤ 20 a) Step 1: Determine and compare the neutron:proton ratios 14 15 28 14 Si  1 29 14 Si   1.0714 14 14 Step 2: Rationalize ▪ Isotopes with atomic number (Z) ≤ 20 and with a neutron (n) to proton (p) ratio of about 1 are more likely to be stable (n ÷ p ~ 1) ▪ Silicon has an atomic number of 14; therefore, 14 Si is more stable 28 b) Step 1: Determine and compare the neutron:proton ratios Prepared by: Engr. N. L. Escalante 29 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  3 5 6 3 Li  1 8 3 Li   1.6667 3 3 Step 2: Rationalize ▪ Isotopes with atomic number (Z) ≤ 20 and with a neutron (n) to proton (p) ratio of about 1 are more likely to be stable (n ÷ p ~ 1) ▪ Lithium has an atomic number of 3; therefore, 36 Li is more stable c) Step 1: Determine and compare the neutron:proton ratios 12 9 23 11 Na  1.0909 20 11 Na   0.8182 11 11 Step 2: Rationalize ▪ Isotopes with atomic number (Z) ≤ 20 and with a neutron (n) to proton (p) ratio of about 1 are more likely to be stable (n ÷ p ~ 1) ▪ Sodium has an atomic number of 11; therefore, 11 23 Na is more stable 2. a) Step 1: Determine the number of protons or neutrons Ni p = 28 n = 31 Cu p = 29 n = 36 Step 2: Rationalize Nickel is more stable than Copper because it has even number of protons. b) Step 1: Determine the number of protons and neutrons Se p = 34 n = 45 Sb p = 51 n = 71 Step 2: Rationalize Selenium is more stable than Tin because it has even number of protons. c) Step 1: Determine the number of protons and neutrons Cd p = 48 n = 64 Au p = 79 n = 118 Step 2: Rationalize Cadmium is more stable than Gold because it has even number of protons. Activity 1: Nuclear Stability: Which is more stable? Self-Assessment No. 1 1. Which isotope in each of the following pairs should be more stable? a) 20 40 Ca or 20 45 Ca b) 15 31 P or 15 32 P c) 10 20 Ne or 10 17 Ne 2. For each pair of elements listed, predict which one has more stable isotopes. b) F or Se b) Co or Ni c) Ag or Cd To be submitted in Google classroom on: Prepared by: Engr. N. L. Escalante 30 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  Radioactivity  Unstable isotopes decompose (decay) by a process referred to as radioactivity. A few such nuclei occur in nature, accounting for natural radioactivity. Many more can be made (induced) artificially by bombarding stable nuclei with high-energy particles. Types of Radioactivity 1. Alpha Emission, α, 24 He ▪ α particles - high energy and low speed - charged particles ▪ an alpha particle is a helium nucleus: 2 p, 2 n, 0 e - ▪ alpha particles are positively charged ▪ α-emission is common for heavier radioactive isotopes i.e., 92U 90 U  2 He or 92U 90 U   238 234 4 238 234 Note: a balanced nuclear equation demonstrates conservation of atomic number and mass number i.e., Σ mass # left = Σ mass # right and Σ atomic # left = Σ atomic # right mass #: 238 = 234 + 4 atomic #: 92 = 90 + 2 Note: we are not concerned with charge considerations in nuclear reactions because they do not affect the reactivity or the transformation products i.e., 24 He not 24 He 2  2. Beta Emission, β, 0 1 e ▪ β particles - high energy and high speed - charged particles ▪ a beta particle is an electron: 0 p, 0 n ▪ beta emission occurs when a neutron is converted to a proton and an electron (emitted from nucleus) ▪ n → p + e- ; note: a new proton is formed; therefore, the atomic no. increases by 1 i.e., 53 I 54 Xe  1 e or 53 I 54 Xe   131 131 0 131 131 234 90 Th234 91 Pa  1 e 0 3. Positron Emission, β+, 1 e 0 ▪ a positron has the same mass as an electron, but is positively charged: 0 p, 0 n ▪ positron emission occurs when a proton is converted to a neutron and a positron (emitted from nucleus) ▪ p → n + β+; a proton is lost ; therefore, the atomic number is decreased by 1 19 K 18 Ar    i.e., 19 K 18 Ar 1e or 40 40 0 40 40 22 11 Na10 22 Ne10e Prepared by: Engr. N. L. Escalante 31 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  4. Gamma Emission,  , 00 ▪  particles - high energy photons, very penetrating ▪ gamma emission has no mass and is not affected by magnetic or electric fields (no charge characteristics) ▪ gamma emission is electromagnetic radiation of high energy, short wavelength (  =10-11 to 10-14 m) stream of high energy particles; emission frequently accompanies other emission processes as a mechanism of energy release ▪ gamma emission is often not included in nuclear equations because it doesn’t change mass or atomic number ex. 5. Electron Capture ▪ occurs when the nucleus ―capture‖an inner-shell electron ▪ 10 e + → ; note: a proton is lost; therefore, the atomic number decreases by 1 i.e., 197 80 Hg  10e197 79 Au 82 37 Rb 10e36 82 Kr Summary: Process Symbol ∆ atomic number ∆ mass number ∆ #n - emission -2 -4 -2 Β - emission +1 0 -1 Β+ - emission -1 0 +1 - emission 0 0 0 Electron capture as reactant -1 0 +1 Activity 2: Application: Types of Radioactivity Self-Assessment No. 2 1. Write the balanced nuclear equation describing alpha emission from Cm-242 2. Write the balanced nuclear equation describing beta emission that forms Al-28 Prepared by: Engr. N. L. Escalante 32 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  3. What type of decay occurs with the transformation of Th-234 to Ra-210? 4. Write the balanced nuclear equations for the following a) Formation of Mn-52 by positron emission b) Formation of Ac-228 by beta emission c) Formation of Np-232 by alpha decay d) Mercury-201 undergoes electron capture e) Thorium-231 decays to form protactinium To be submitted in Google classroom on: Nuclear Binding - is the minimum energy required to disassemble a system of particles into separate parts E  mc 2 m change in mass = mass products - mass reactants c speed of light = 3 x 108 m/s Example: Binding energy of 24 He Helium has 2 protons, 2 neutrons and 2 electrons, so we can consider that the mass is the sum of 2 hydrogen atoms and two neutrons ( H atom has 1 p + and 1 e- ) 4 2 He 211H 201n 1 H = 1.00728 amu 1 n = 1.00867 amu Observed ,ass pf He-4 atom = 4.0015 amu 1 amu = 1.66054 x 10-27 kg Hence m = 2(1.00867 + 1.00728) - 4.0015 m = 0.0304 amu m = 0.0304 amu x 1.66054 x 10-27 kg / amu m = 5.04804 x 10-29 kg E  mc 2 E = (5.04804 x 10-29 kg)(3 x 108 m/s)2 E = 4.54324 x 10-12 J For a mole of 4 He nuclei, the energy released is E = (4.54324 x 10-12 J)(6.022 x 1023 / mol) E = 2.7359 x 1012 J/mol = 2.7359 x 109 kJ/mol Ex. Calculate the binding energy of C-14, in kilojoules per mole. Prepared by: Engr. N. L. Escalante 33 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  NATURAL RADIOACTIVITY Radioactive Decay Series Many heavy elements undergo several sequential emissions before forming a more stable nuclei: The Kinetics of Radioactive Decay Whether or not a given isotope is radioactive is a characteristic of that particular isotope. Some isotopes are stable indefinitely, while others are radioactive and decay through a characteristic form of emission. As time passes, less and less of the radioactive isotope will be present, and the level of radioactivity decreases. An interesting and useful aspect of radioactive decay is half-life, which is the amount of time it takes for one-half of a radioactive isotope to decay. The half-life of a specific radioactive isotope is constant; it is unaffected by conditions and is independent of the initial amount of that isotope. The rate of decay for radioactive isotopes is a first order process and obeys the integrated rate for first order kinetics: A  An  A0ekt ln n   lne  kt   A0  An A   e kt ln n   kt A0  A0  where: An amount remaining after time t A0 amount at t = 0 t time k rate constant The half-life, t1 / 2 , is the time it takes for half of the nucleids to decay. 1 In symbols: An  A0 ln1  ln 2  kt1/ 2 2 A  Substitute in: ln n   kt  ln 2  kt1/ 2  A0  1   A0  ln 2 We get: ln 2   kt1/ 2 k  A0  t1/ 2     1 ln   kt1/ 2 2 Prepared by: Engr. N. L. Escalante 34 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  Activity can be expressed in terms of the number of atoms decaying per second, or Becquerels (Bq). 1 Bq = 1 atom/s Alternatively, activity may be cited in disintegrations per minute or, perhaps most commonly, in Curies (Ci). 1 Ci = 3.70 x 1010 atoms/s Example Problems 1. The half-life of radium-226 is 1.6 x 103 years. a) Calculate k in s-1. b) What is the activity in curies of a 1.00-g sample of Ra-226? c) What is the mass in grams of a sample of Ra-226 that has an activity of 1.00 x 10 9 atoms/min? Solution: a) kt1/2 = 0.693 k= s-1 b) A = kN; where A – activity; N – number of radioactive nuclei present N = 1.00 g x x A= = 0.989 Ci c) N = = Mass = 2. Iodine-131 has a half-life of 8 days. If there are 200 grams of this sample, how much of I- 131 will remain after 32 days? Given: t1 / 2 = 8 days A0 = 200 g Required: An at t = 32 days Solution: Solve for the rate constant, k ln 2 0.6931 k   0.08664/ day t1/ 2 8days An  A0ekt An  (200g )e(0.08664/ day )( 32days ) An  12.50g of I-131 remains after 32 days 3. Sodium-24 has a half-life of 15 hours. If there are 800 g of Na-24 initially, how long will it take for 750 g of Na-24 to day? Given: t1 / 2 = 15 hours A0 = 800 g Prepared by: Engr. N. L. Escalante 35 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  Required: t if An = 800 g - 750 g = 50 g Solution: Solve for the rate constant, k ln 2 ln 2 k   0.0462/ hr t1/ 2 15hr A  ln n   kt  A0   50g  ln   (0.0462/ hr)t  800g  t  60hr for 800 g of Na-24 to decay until 50 g of Na-24 remains or the time it takes for 750 g of Na-24 to decay Activity 3: Kinetics of Radioactive Decay Self-Assessment No. 3 4. Plutonium-239 (produced in breeder reactors has a half-life of 24,100 years. How long will it take for a sample of plutonium-239 to decay to 0.100% of its original value? 5. It takes 35 days for a 512 g sample of element X to decay to a final amount of 4 g. What is the half-life of the element X? 6. The half-life of Oxygen-15 is 2 min. What fraction of a sample of O-15 will remain after 5 half lives? To be submitted in Google classroom on: Dating Artifacts by Radioactivity Carbon-14 Dating  t1/2 = 5730 yr  While alive, plants constantly replace carbon-14  After death, the carbon-14 will decay at a known rate Example: Determine the date of a fossil when the reactive 14C abundance is 0.038 compared to living tissues. Solution: K = 0.693/t1/2 = 0.693/ 5730 yrs = 1.21 x 10-4 yr-1 ln(An/Ao) = -kt t = -ln(An/Ao)/k = -ln(0.038/1.000)/1.21 x 10-4 yr-1 t = 2.70 x 104 yrs Prepared by: Engr. N. L. Escalante 36 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  Nuclear Transmutation Transmutation is the change of one element to another as a result of bombardment of high energy particles (e.g. neutrons, electrons, and other nuclei) ▪ Rutherford prepared the 1st synthetic nuclide, 17 O , in 191; Irene Curie prepared the 1st radioactive nuclide, 30 P , in 1934 ▪ All trans-Uranium elements (Z > 92) are both synthetic (man-made) and radioactive. ▪ Nuclear transmutations can show alpha, beta, and gamma emissions as well as production of protons e.g. 13 Al  2 He15 P 0 n 27 4 30 1 Nuclear Fission Fission - a nuclear reaction that releases energy as a result of splitting of large nuclei into smaller ones. Nuclear power pants use fission to split U-235 to produce energy. 1. U-235 is bombarded with slow neutrons - this produces smaller nuclei as well as more neutrons and energy. 2. A chain reaction results because each neutron produced can cause fission of another U-235 nucleus. e.g. 92U  0 n 56 Ba 36 Kr 30 n 235 1 142 91 1 235 U 234.9934 amu 92 Kr 91.926270 amu 141 Ba 140.914363 amu 1 0n 1.00867 amu m = -0.135427 amu = -2.2488 x 10-28 kg E = -2.0239 x 10-11 J = -1.2188 x1010 kJ/mol Critical mass - minimum mass required to sustain a chain reaction. Control rods are made of B or Cd; these rods absorb neutron so the process doesn’t accelerate too rapidly. Rods are raised to control the speed of the process. Fuel rods are made of U-235. 238U is the most abundant U isotope but is not fissionable so uranium must be enriched to increase the amount of 235U. Moderator - slows down the neutrons. Water or other liquid coolant surround rods. The water serves to 1) slow down neutrons so they can collide with U-235; 2) transfer heat to steam generator. Primary problems with nuclear power plants 1. Safety (Chernobyl and Three Mile Island had cooling system failures that led to reactor meltdowns. Chernobyl also did not have containment building around reactor) 2. Nuclear Wastes - some products will remain radioactive for thousands of years. Nuclear Fusion Fusion - a nuclear reaction that releases energy as a result of the union of smaller nuclei to form larger ones. It occurs in the upper atmosphere and outer space; reactions that power the sun and stars. 1 1 H 11H 12H  10e 1 1 H 12H 23H Prepared by: Engr. N. L. Escalante 37 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.  3 2 H  23H 24H  211H 3 2 H 11H 24H  10e Fusion generates even more energy than fission and creates little radioactive waste, so it would provide a wonderful source of energy - fusion is attractive as a potential alternative power source, but fusion requires very high temperatures (tens of millions of degrees Celsius) in order for nuclei to overcome strong repulsive forces - magnetic fusion reactors are being designed and tested. Applications of Radioactive Isotopes ▪ Nuclear power plants ▪ Medical diagnosis and treatment, e.g., PET scan monitors glucose metabolism in brain using C-11 isotope; I-131 measures activity of thyroid ▪ Carbon dating (measure amount of C-14 remaining in a sample) ▪ Synthesis of new elements ▪ Irradiation of food - preserves food & destroys parasites ▪ Nuclear weapons (atomic bombs and H bombs) EXPLAIN To be able to translate your understanding of nuclear chemistry and energy, do the following activity. Activity 4: Check Your Understanding on Nuclear Chemistry and Energy Self-Assessment No. 4 1. How do nuclear reactions differ from ordinary chemical reactions? 2. State the general rules for predicting nuclear stability. 3. Outline the principle for dating materials using radioactive isotopes. 4. What is the difference between radioactive decay and nuclear transmutation? To be submitted in Google classroom on: ELABORATE & EVALUATE Activity 5: Nuclear Fission and Fusion Self-Assessment No. 5 1. From your understanding of nuclear fission, explain how an atomic bomb works. 2. Why do heavy elements such as uranium undergo fission while light elements such as hydrogen and lithium undergo fusion? 3. What are the advantages of a fusion reactor over a fission reactor? What are the practical difficulties in operating large-scale fusion reactor? To be submitted in Google classroom on: Prepared by: Engr. N. L. Escalante 38 Property of and for the exclusive use of SLU. Reproduction, storing in a retrieval system, distributing, uploading or posting online, or transmitting in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise of any part of this document, without the prior written permission of SLU, is strictly prohibited.