AP Chemistry Chapter 23 Notes

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AP Chemistry Chapter 23 Notes. Henri Becquerel ruined some photographic plates with x-rays from a uranium source and radioactive decay was discovered in 1896. Henri Becquerels experiment (1896) - PowerPoint PPT Presentation


  • AP Chemistry Chapter 23 Notes

  • Henri Becquerel ruined some photographic plates with x-rays from a uranium source and radioactive decay was discovered in 1896.

  • Henri Becquerels experiment (1896)Tried to see if fluorescent minerals would give off X-rays. Set some out in the sun with covered photographic film. If minerals gave of X-rays when they fluoresced, the film should darken and it did.Accidentally set some of these minerals in a dark drawer for a few days with undeveloped film, and was surprised to see the film strongly exposed. He knew they gave off X-rays when charged by the sun - but these results suggested the X-rays were coming from the mineral itself Natural Radioactivity No external energy source required!

  • RadioactivityOne of the pieces of evidence for the fact that atoms are made of smaller particles came from the work of Marie Curie (1876-1934). She discovered radioactivity, the spontaneous disintegration of some elements into smaller pieces.

  • Marie and Pierre Curies experiments with pitchblende Discovered Radioactive Naturally occurring elements, particularly Uranium, Radium, and Polonium. Curium was named after Marie posthumously

  • THE GREAT DISCOVERY W.K. Roentgens experiment (1895) - Fluorescence Certain substances will absorb photons of energy when exposed to a source (i.e. cathode rays, the sun), and then emit them over a period of time thus they glow in dark when exposed to UV lightCathode rays beams of electrons Cathode ray tube (CRT) Vacuum tube that has electric current passed through it .Component of television sets thats why they call it the tube X-rays Name given by Roentgen to unusual stray energy observed to cause fluorescence across the room when CRT was used X-ray because he did not know what the heck it was.and the name stuck

  • BETA PARTICLESConsists of high speed electron (from disintegration of neutron)Tissue damage potential much greater than AlphaHarmful if ingested? not as much as AlphaCan be blocked? by glass, will penetrate skin

  • GOLD FOIL EXPERIMENTErnest Rutherford and the Gold Foil Experiment Disproved Thompsons plum pudding modelProved the existence of a nucleus with a positive charge

  • Consists of He nucleusTissue damage potential great if internalizedHarmful if ingested? yup, veryCan be blocked? by layer of skin, or cardboardNote that atoms are NOT conserved in nuclear reactions, but mass numbers and atomic numbers are.ALPHA PARTICLES

  • NUCLEAR RADIATIONErnest Rutherford and the Lead block experiment (1899) -Alpha rays ()Beta rays ()Gamma rays ()

  • How did Rutherfords gold foil experiment change the theory of the structure of the atom?


  • ARCHITECTURE OF THE ATOM Atomic Number Number of protonsDetermine what type of element an atom is

    Mass Number Sum of total number of protons and neutrons in an atomCan change for an element depending upon the number of neutrons present

    Isotopes Elements with the same atomic number, but different mass numbersDue to the difference in number of neutronsExample:C-14 and C-12H-1, H-2, and H-3

    Radioisotope Isotope that is unstable and undergoes decay, thus giving off radiation

  • Subatomic Particles

  • Common IsotopesIsotopes of Particular interest C-14 used in radiocarbon dating I-131 used in thyroid cancer treatmentU-235 used in nuclear power

  • ISOTOPES IN NATURE Atomic Mass -Weighted Average mass of all existing isotopes of an element Can be calculated by: (percent isotope 1)(molar mass isotopes 1) + (percent isotopes 2)(molar mass isotope 2) +.. Try this with your grades as an example. Final grades will be determined by giving homework 10%, labs 30%, and tests 60% Homework grade = 85%Lab grade = 80%Test grade = 60% Final grade = (.10)(.85) + (.30)(.80) + (.60)(.60) = .69

  • Nuclear Section B Introduction

    Approx. 90 known naturally occurring elementsApprox. 350 known isotopes in our solar systemApprox. 70 of these radioactiveApprox. 1,600 Lab created isotopesRadioactive just means unstable it naturally decaysThere is a rather constant level of natural radiation in our environment called background radiation


  • Spontaneous Radioactive Stability Production of an particleProduction of a particleProduction of raysSpontaneous Fission

  • 1. production of a particle

  • 2. production of b particle

  • 3. production of g rays

  • 4. Spontaneous Fission

  • DECAY SERIESShows the nuclear decay steps that occur when a radioactive isotope decays to a final stable product

  • II. Nuclear Fission

  • Sub-CriticalCriticalSupercritical

  • then radioactive decomposition: life = 1.3 sec

  • then radioactive decomposition: life = 1.3 sec

  • then radioactive decomposition: life 18.3 months

  • then radioactive decomposition: life 18.3 months

  • Other Types of Nuclear ReactionsK-capture: the capture of an electron from the first or K shell

  • Other Types of Nuclear ReactionsPositron (0+1b): a positive electron

  • Formation of a NeutronAn electron and proton combine to form a neutron.0-1e + 11p --> 10n

  • fewer protonsmore protonsLessmass

  • III. Nuclear FusionExample #1Requires 40,000,000 K to overcome electrostatic repulsion

  • Half life SM x (1/2)n = EM(1/2)n = EM / SM or EM / SM = (1/2)n

    n Log (1/2) = Log (EM / SM)

    n = Log (EM / SM) / Log (1/2)

    n = t / t1/2 life

  • ln (N/No) = ln (1/2)n

    ln (N/No) = - kt

    t1/2life k = ln (1/2) = 0.693

    t1/2life = 0.693/k

    A = kN

  • thus, N/Not = - kN1

    where N = amount [conc or counts]and k = rate constant

    dN/dt = - kN

  • Half-life : time when

  • Half-life

  • Binding Energyenergy released during degradation of a nucleus

  • E = mc2Energy = mass x speed of light21 gram of mass = 9 x 1013 joules = amount of energy needed to power your house for 1,000 years

  • E = mc2

    or E = c2m

    where c = 3.00 x 108 m/sec

  • Nuclear Fission: Splitting of an atom into 2 or more daughter particlesIf daughter particles are unstable, then they will be radioactive

  • Fission Chain Reaction

  • Hydrogen bombs

  • Results of fission reactions

  • IONIZING RADIATION HOW MUCH IS SAFE?Rem Roentgen equivalent to man1Rem = 1000 mRemDoes not matter what type of radiation it is, it still has the same ionizing effect on living tissue1 mRem of exposure to radiation increases risk of cancer death by 1 in 4 millionTwo things to consider:Radiation densityRadiation dose

  • RADIATION DAMAGE: NOW AND LATERRadiation damage to your body can occur in several ways:Break apart essential moleculesproteins (i.e. enzymes)nucleic acids (i.e. DNA)Mutations

    Kills cellsMutates sperm/ovaCancerGovernment recommends no greater than exposure to 500 mrem per year for general public

    Government recommends no greater than 5,000 mrem per year from the workplace

  • Table of Factors Effecting Biological Damage from Radiation

    FactorEffectDoseIncrease in dose produces proportional increase in riskExposure timeSpreading out over time decreases riskArea ExposedLarger area means greater riskTissue typeRapidly dividing cells more susceptible

  • Radiation effects by dosage

  • EXPOSURE TO RADIATIONExposure to radiation can come from:Cosmic RaysRadioisotopes in rocks, soil, water, airFallout from nuclear weapons testingAir travelRadioisotope release from nuclear power generation Government recommends no greater than exposure to ______________for general public

    Government recommends no greater than ___________ per year from the workplace


  • Radon gas comes from: Gas released from earth (from Uranium decay

    Radon gas exposure can lead to: lung cancer

    ___________% of lung cancer deaths are caused by radon exposure.

    ___________% of households in the U.S. have higher than recommended radon levels.



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