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Nuclear Chemistry

by: Alexi Martin

Nuclear Chemistry CHEM 1200

Alexi Martin
GPA 3.58

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About this Document

these notes cover ch 21
Chemistry II
Dr. Alexander Ma
Class Notes
Chemistry Nuclear
25 ?




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This 5 page Class Notes was uploaded by Alexi Martin on Friday April 15, 2016. The Class Notes belongs to CHEM 1200 at Rensselaer Polytechnic Institute taught by Dr. Alexander Ma in Spring 2016. Since its upload, it has received 8 views. For similar materials see Chemistry II in Chemistry at Rensselaer Polytechnic Institute.


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Date Created: 04/15/16
Ch 21 Nuclear Chemistry    Nuclear Medicine  ­nuclear radiation for tests­ labelling intake and output  ­nuclear radiation is ionizing tracks have unhealthy tissue  Discovery of Radioactivity  ­phosphorescent minerals give off x­rays  ­emission of light­ glow caused by radiation  ­Certain minerals produce energy rays that could penetrate matter  1. Contained Ur  2. All rays produced not exposed to outside energy  ­uronic rays­ U like x­rays not related to the glowing  ­energy produced without energy input  Curies  ­ electroscope= uronic rays  ­ Specific elements other than U­ such as Ra and Pl  Electroscope  ­ Metal foils spread out due to like charge repulsion  ­ Ionizing radiation tracks electrons off air discharge than electron repulsion  Radioactivity  ­ Ionize matter from uncharged to charged matter  ­ Increase in energy  ­ Penetrate matter  ­ Phosphorescence of chemicals causes them to glow  ­ Release of tiny increasing in energy particles (gamma rays)  ­ Ejected from nucleus  Types (increasing in ionization power and decreasing in penetration)  alpha particles  ­charge of +2 protons with mass 4 amu  ­nucleus of He 2+  ­can be stopped by 0.01 mm of lead  Beta  ­ Charge ­1   ­ Electrons negligible mass  ­ Stop by 1 mm Pb  ­ E­ like  Gamma  ­ Form of light energy  ­ Stopped by 100 mm of lead  Electron capture lower level electrons are pulled into nucleus  Unstable nuclei emit positrons, + charge e­ (e+) anti matter  Nucleus  1  ­ Small volume, however entire mass of the atom, very dense, strong force holds it  together  ­ Protons and neutrons together are called nucleons  ­ Proton number + atomic number= (Z)  ­ Atoms of sure elements have different numbers of neutrons (also known as isotopes)  A= Z+neutron  ­ Neutrons = A­Z  ­ Nucleus of isotope (nuclide) 10 % of known are radioactive, they have radioactive  nuclides  ­ Element­ mass number­> X­A such as C­13  Mass number= element    ^A x\/Z  Atomic number  Radioactivity  ­ Radioactive nuclei spontaneously decay into smaller nuclei that are unstable, nuclide  emits particles or energy  ­ Parent nucleus undergoing radioactive decay  ­ Daughter nuclei new nucleus formed  ­ All nuclides of 84 or more atomic number are radioactive  Transmutation  ­ 1 element changed into atoms of a different element  ­ # protons must change  Chemical vs. Nuclear  ­chemical = atom gain or share e­  no charge  ­nuclear structure or nucleus number of protons change, creating a different element  Nuclear equations (nuclear processes)  ­symbol of nuclide=nucleus  ­A& Z  conserved, can predict daughter nuclei  Alpha emission  Most ionizing but least penetrating  (298,88) Ra­> 4,2 He+ Rn (218,86)  X­> ­2 X+ 2,4 He  Beta emissions  ­ Moves faster, produced from nucleus  ­ 1 times more penetrating and ½ as ionizing  ­ Loss of beta, A increases by 1 Z=same  ­ (234,90) Th­> 0,­1 e+ 234,91 Pa  ­ 1,0 n­> 1,1p+ 0,­1 (e­)  Gamma Emission  ­ Increase energy photons of electromagnetic radiation  ­ A & Z are the same  ­ No loss particle, no change in composition  ­ Decrease in ionizing and increase in penetrating  ­ After nucleus undergoes other types of decay  2  ­ X­>X+gamma  Positron Emission  ­ Charge +1 no mass antielectron  ­ Similar to beta in ionizing and penetrating  ­ Loose e+ Z+same  A decreases by one  ­ Proton­>neutron  Electron capture  ­inner orbital e­ into nucleus­ unstable  ­ no particle emission, same result as positron  ­e­+p+­>n  ­A decreases by one Z=same  1,1 p+ 0,­1 e­>1,0 n  Nuclear equation  ­ Mass number and atomic number conserved  ­ Determine identity of daughter nuclei if we know parent and method of decay  Example 1 : ​  in order to see all examples accurately need to look on powerpoint  What causes nuclei to decompose  ­ Held together by strong force  ­ Neutrons stabilize their nucleus  N/Z ratio  ­ Neutrons to protons ratio important to stability   ­ N/Z increase neutrons­ to protons via beta decay  ­ N/Z decrease protons to neutrons via positron emission  or e­ capture  ­ Z=1=20 is stable  ­ Z from 20 to 40 stable 1.25  ­ Z from 40 to 80 stable  ­ Z greater than 83 unstable  Example 2: M ​g­22 Z=12 N=10 10/12<1 more reactions  ​unstable positron emission or electron  capture  Example 3:​  Kr 39 49/36=1.36 increase ratio so less reactions b ​eta emission causes ratio to  decrease to 1.29  Magic number  ­N/Z actual number of protons and neutrons affect stability  ­stable even over odd  ­few odd  ­total number of nucleons add to magic number=stable  ­stable when N= 2 8 20 28 50 82 or 126  Decay series  ­ Native 1 radioactive nuclei another  ­ Daughter also radioactive until stable  ­ decay series­ steps large unstable radioactive nuclei to stable  1. Count beta and alpha decay  2. Z number ­4 alpha  3  3. A ­2 alpha +1 for beta  Example 4: s​ee powerpoint to understand process 8 ​2 Pb  Detecting radioactivity  ­ radioactive exposed film  ­Electroscope penetrate flash and ionize air  ­ Geiger counter works by counting e­ when Ar is ionized  ­scintillation counter counts # of flashes per minute  Natural Radioactivity  ­ Food  ­ Small amounts of radioactive materials in air, ground and water  ­ Background radiation  Rate of Decay  ­ Constant rate of change, different for each isotope  ­ Radionuclide has a particular length of time­ constant ½ life  ­ Rate of radioactivity not affected by temperature  ­ rate=kN     t ½=0.693/k  ­ Shorter the half life the more nuclei decay every second sample ‘hotter’  Ln Nt/N0= ­kt= ln rate t/rate 0=ln mt/m0  Example 5: m​t=? Ln Nt/N0= ­kt t1/2=0.693/k  k=0.693/t1/2 =0.693/2.864=0.2423 1/yr  Nt=1.35e^ ­(0.2423)5  Nt= 0.402 mg  Example 6: ​t1/2=0.693/k k=0.693/3.8=0.182 1/day lnx/10.24 (37.8 days)=0 ​.011 g  Radiometric Dating  ­ Change in the amount of radioactivity of radionuclide measuring, or parent radioactive  isotope and its stable daughter (half life and previous equations)  ­ Mineral geological dating  Radio C dating  ­ 3 isotopes C­14 half life 5730 years (C­13, C­12)  ­ C­14/C­12 constant because it is replenished ratio decreases after death, compared to  natural ratio to determine death date ( 50,000 years limit)  Example 7: 4​.5 dis/mingC living 15.3 dis/mingC how old?  k=0.693/t1/2­0.693/5730= 1.209x10^­4 1/yr  (Ln 4.5/15.3)/1.209x10^­4 =​1x10^4 yr  Example 8:​ t 1/2ln2/k k­0.693/5730=9x10^­4  ratex=ratee^­kt=20e^­1.29x10^­4=3 ​.03 counts/mincG  Nonradioactive nucleic charges  ­ Nucleus unstable hit by between = 2 smaller nuclei is fission  ­ Small nuclei acceleration added together= larger nucleus fusion  ­ Fusion releases more E than fission  Fission chain reaction  ­reactant is also part of the product  ­fission= neutrons  ­ejected from U before they hit U­235 or absorbed by U­238  4  ­need critical mass  Fissionable material  ­ U­235 Pu­239 Pu­240  ­ U needs to be enriched in U­235  Nuclear Power  ­ fission=electricity  ­ Heat boils water into steam, steam turns turbine into energy  ­ No air pollution, more efficient  ­ core= fuel rods, subcritical  ­ Between fuel rods control rods neutron absorbing B and/or Cd  ­ Moderator to slow down ejected neutrons  Pressurized light water  ­water coolant and moderator, fuel U  E fission  E=mc^2  Mass Defect  ­ nucleus=energy  ­ Difference in mass between separate nucleons and combined nucleus   ­ E released binding E  ­ 1 Mev­1.602x10^­13 J 1cimumd=931.51 Mev  ­ Increase BE per nucleon the more stable nucleus is  Example 9: ​ mass defect= 6(1.00783)+10(1.0366)­16.01470=0.118879 amu  0.118879x931.5=110.74 MeV/16=6 ​.921 MeV/nucleon  Example 10:​  mass defect= 26(1.0078)+30(1.0086)­53.9344=0.52844  0.52844x931.5=492.2/56=​ 8.790 MeV/nucleons  Nuclear fusion  ­ Lighter nuclei to create more stable heavier nuclei  ­ Sun uses this to turn H to He  ­ Increase in energy, fission to create fusion (see pp for equation)  Artificial transmutation  ­ Increase in energy particles smashed together into target nuclei creates new nuclei  ­ Can be radiation or charged particles  ­ (see pp for equations)  ­ Bombardment of 1 nucleus with another= new atoms, also new neutrons  ­ Performed in a particle accelerator (linear, cyclotron)  Example 11: see powerpoint for equations and answers         5 


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