Chapter 8 Nuclear Chemistry
Post on 04-Jan-2016
DESCRIPTIONChapter 8 Nuclear Chemistry. Radiation. The emission of energetic particles The study of radiation and the processes that produce it is called nuclear chemistry. Unlike the chemistry we have studied to this point, nuclear chemistry often results in one element changing into another one. - PowerPoint PPT Presentation
RadiationThe emission of energetic particlesThe study of radiation and the processes that produce it is called nuclear chemistry.Unlike the chemistry we have studied to this point, nuclear chemistry often results in one element changing into another one.
TragedyApril 26, 1986, 1:24 amV.I. Lenin nuclear power plantChernobyl, USSRExplosions in reactor 4 31 immediate deaths, 230 hospitalizations, countless exposures to high-level radiationThe aftermath continues to this day.
ChemistryChemistry as studied up to this pointAtomic and molecular changes involve electrons.Atoms react to achieve a stable octet electron configuration.
Nuclear chemistryAtomic changes involve the nuclei.Nuclei emit energetic particles we call radiation.
BecquerelDiscovered that his paper-wrapped photographic plate was exposed by uranium-containing crystals.This disproved his hypothesis linking exposure to UV light with phosphorescence.But it revealed a brand-new phenomenon that he called the emission of uranic rays.
Marie and Pierre CurieSearched for the elements that produced the uranic raysDiscovered two new emitters of uranic rays; one was a new element (polonium)Radioactivity not the result of a chemical reactionSince the rays were not unique to uranium, a new term was proposed: radioactivityDiscovered radium as a result of its extreme radioactivity
RadioactivityCharacterized by RutherfordThe result of nuclear instability
Alpha RadiationComposed of particles consisting of two protons and two neutronsRepresented by the symbol for a helium nucleusHigh ionizing powerLow penetrating power
Writing Nuclear Reaction Equations Identify the type of nuclear reaction and the particle(s) involved.The sum of mass numbers and the sum of the atomic numbers must balance on both sides.
Concept Check 8.1Identify the daughter nucleus from the alpha decay of I-131
Concept Check 8.1 SolutionAlpha decay of I-131 results in the loss of a helium nucleus and the formation of Sb-127 as the daughter nucleus.
Beta RadiationComposed of particles consisting of energetic electrons represented by the symbol .Smaller than alpha particles, so more penetratingBut this also means less ionizing powerIn beta decay, a neutron converts to a proton, emitting an electron and increasing the atomic number by 1.
Concept Check 8.2Identify the daughter nucleus from the beta decay of C-14
Concept Check 8.2 SolutionBeta decay of C-14 involves the loss of an electron from the nucleus. Like alpha decay, the atomic numbers and atomic mass numbers from each side must balance.
Gamma RadiationAn energetic photon emitted by an atomic nucleusRepresented by the symbol gGamma rays are electromagnetic radiation, not matter.Highest penetrating power, lowest ionizing power
Concept Check 8.3Considering the three type of radiation, alpha, beta, and gamma,Order them according to increasing penetrating power.Order them in according to increasing ionizing power.
Concept Check 8.3 SolutionAlpha particles are large and carry a 2+ charge, therefore do not penetrate very far but have tremendous ionizing power. Beta particles are high energy electrons with 1 charge, therefore smaller and have greater penetrating power and moderate ionizing ability. Gamma rays are electromagnetic radiation and not matter, therefore, have no mass or charge and possess great penetrating power but low ionizing ability.Penetrating power: alpha < beta < gammaIonizing power: gamma < beta < alpha
Half-LifeThe time required for half of the nuclei in a sample to decay
Concept Check 8.4Radon-222 decays via alpha emission to Po-218 with a half-life of 3.82 days. If a house initially contains 800. mg of radon-222, and no new radon enters the house, how much will be left in 15.3 days? How many alpha emissions would have occurred within the house?
Concept Check 8.4a SolutionInitial amount of radon-222 (half-life of 3.82 days): 800. mg (a) How much will be left after 15.3 days?(b) How many alpha emissions occurred?First determine how many half-lives have passed by dividing the total time passed by the half-life:
Concept Check 8.4b Solution(b) How many alpha emissions occurred in 15.3 days?800. mg 50.0 mg (left) = 750. mg of radon-222 decayed.Each decay of an atom of radon-222 is an alpha decay.
Nuclear FissionGeneral idea: If nuclei emit particles to form lighter elements, they might also absorb particles to form heavier elements.
The result would be a synthetic element.
Nuclear FissionFermi hoped to make a synthetic element with atomic number 93.He detected beta emission following his neutron bombardment of uranium.Subsequent experiments by Hahn, Meitner, and Strassman seemed to confirm Fermis work.
Nuclear FissionJust before the outbreak of WWII, Hahn, Meitner, and Strassman reported that no heavier element was detected; rather two lighter elements were formed.Previous nuclear processes had always been incremental.Contradicting all previous experiments in nuclear physics, they proposed a model for the fission of uranium atoms based on absorption of neutrons.Large amounts of energy were also emitted during fission.
Nuclear FissionWeeks later, U-235 fission was proposed as the basis for both a chain reaction and a bomb of inconceivable power.
Enrico Fermi and Leo SzilardEnrico Fermi and Leo Szilard constructed the first nuclear reactor at the University of Chicago; they achieved a self-sustaining, controlled fission reaction lasting 4.5 minutes.
The Manhattan ProjectThe largest scientific endeavor of its time, the race to beat Germany to the atomic bomb was code-named Manhattan Project.Collection and synthesis of fissionable fuel (U-235 and Pu-239) were pursued at Oak Ridge, TN and Hanford, WA. J. Robert Oppenheimer directed bomb design at Los Alamos, NM.
Critical Mass: Fissionable FuelLesser masses of fissionable material will not undergo self-sustaining fission; too many neutrons are lost to the surroundings instead of being absorbed by other U-235 nuclei.After the successful controlled reaction, the goal became the construction of a device where fission would spiral out of control.
Atomic Bomb: Fat Man and Little BoyTwo designs were constructed and a successful test carried out on July 16, 1945. Two atomic bombs (one uranium and one plutonium) were dropped on Japan only weeks later.Little BoyUraniumCannon-like barrelFat ManPlutoniumSqueezed by implosion
Nuclear PowerNuclear reactors are designed to produce a controlled fission reaction.Uranium rods are interspersed with control rods of neutron-absorbing material, usually boron or cadmium.Heat of fission boils water to produce steam, which turns the turbine to produce electricity.
Nuclear vs. Coal-burning Power PlantsNuclearUses 100 lb. of fuel per dayProduces enough electricity for a city of 1 million peopleDoes not produce air pollution, greenhouse gases, or acid rainProblems include waste disposal and accidentsCoal-burningUses 5 million lb. of fuel to produce an equivalent amount of energy
Waste DisposalUranium oxide pellet fuel assemblies are replaced with fresh fuel every 18 months.Most spent fuel is currently stored on-site.1982 Nuclear Waste Policy ActEstablished a program to build an underground nuclear waste repositoryYucca Mountain, NV is the controversial site of this much-delayed project.
Nuclear AccidentsNuclear power plants cannot detonate like nuclear explosions.Enriched uranium at 3% U-235 vs. 90% U-235Three Mile Island: March 28, 1979Chernobyl: April 26, 1986Fukushima Daiichi Nuclear Power Plant, March 11, 2011Superior power plant design in the U.S. has meant no accidental nuclear deaths; nevertheless public support for nuclear power is chilly.
Mass DefectMass defect is the difference between the experimentally measured mass of an atom and the sum of the masses of individually measured protons, neutrons, and electrons.The missing mass was converted to energy when elements form from constituent protons and neutrons.This energy is related to the mass defect by Einsteins equation E = mc2.
Nuclear Binding EnergyEinsteins equation E = mc2 represents the energy that holds a nucleus together.The highest values for this binding energy are for elements with mass numbers close to 56.
Nuclear Binding Energy
Nuclear Binding Energy: Fission
The products have higher binding energy than the reactants; it follows that the products weigh less.The missing mass is converted to energy according to E = mc2This difference in binding energy is the source of the energy liberated in fission.
FusionIn fusion, the nuclei of lighter elements are fused into heavier ones.Like fission reactions, the products of fusion have higher nuclear binding energies, so energy is released.Fusion releases ten times more energy per gram than fission.Fusion is responsible for the suns energy and is the basis of modern nuclear weapons.
Controlled FusionAdvantagesPotential for an almost limitless source of energy for societyLess radioactive waste productsNaturally occurring deuterium in water is a reactant and abundant.Disadvantages/obstaclesHigh temperatures required and a lack of materials available for containmentCurrent production methods consume more power than they produce.
Radiation and Human LifeRadiation can destroy biological molecules.Low-level alpha emitters present little danger externally, but once ingested have access to internal organs.Danger is usually overstated by the popular press.rem: most common unit for measuring human exposureExposure, on average, per year, is 1/3 rem.
Possible EffectsThe human body can repair itself and suffer no adverse effects.Abnormal growth can begin that leads to cancerous tumors.Damage of intestinal lining leads to radiation sickness, hampering the intake of nutrients and water.Damage to the immune system allows infection to go unchecked.Genetic defects in offspring have occurred in laboratory animals.
RadonRadon is the major source of human radiation exposure.Naturally occurring uranium deposits in the earth lead to the collection of radon in residential basements.Significance of radon as a health threat is controversial.
Carbon DatingCarbon-14 is created in the upper atmosphere and becomes incorporated in living tissue at a constant level, then drops after death.The half-life of C-14 is 5730 years.Levels of C-14 in carbon-based artifacts are compared to modern levels as an age signature.The Shroud of Turin analysis determined the age of the materials in the shroud.
Concept Check 8.5A fossil has a carbon-14 content that is 12% of that found in living organisms. Estimate the age of the fossil.
Concept Check 8.5 SolutionA fossil has a carbon-14 content that is 12% of that found in living organisms.
After 3 half-lives (17190 years), 12.5% of the C-14 in the sample remains, therefore the sample is slightly older than 17190 years old.
The Age of the EarthU-238 is used to measure longer periods of time.
It decays to lead with a half-life of 4.5 109 years.
Lead levels in artifacts are used as an age signature.
Uranium to lead dating
Concept Check 8.6A moon rock is found to contain 50% uranium and 50% lead. How old is the moon rock?
Concept Check 8.6 SolutionA moon rock is found to contain 50% uranium and 50% lead. How old is the moon rock?
After 1 half-life, the original amount of uranium will be reduced to 50%, therefore, the rock is about 4.5 million years old.
Nuclear MedicineDiagnosisRadioactive elements concentrate in specific areas of interest in the body.Gamma emitters will expose photographic film, allowing images of organs to be recorded.TherapyRadiation can destroy cancerous tumors.Minimizing exposure of healthy tissue is a challenge.
Chapter SummaryMolecular ConceptRadioactivityAlpha radiationBeta radiationGamma radiation Half-lifeFissionCarbon datingSocietal ImpactThe discovery of radiation ultimately led to the creation of the first atomic bomb.Nuclear power is used widely throughout the United States.