radioactivity chapter 25. nuclear chemistry study of the structure of atomic nuclei changes they...

Download Radioactivity Chapter 25. Nuclear chemistry study of the structure of atomic nuclei changes they undergo. Nuclear Radiation

Post on 03-Jan-2016




0 download

Embed Size (px)


  • RadioactivityChapter 25

  • Nuclear chemistrystudy of the structure of atomic nuclei changes they undergo. Nuclear Radiation

  • Wilhelm Roentgen (18451923) 1895-invisible rays were emitted when electrons bombarded the surface of certain materials. The Discovery of Radioactivitycaused photographic plates to darken.named the invisible high-energy emissions X rays.

  • Henri Becquerel (18521908) was studying phosphorescence minerals that emit light after being exposed to sunlightThe Discovery of Radioactivityphosphorescent uranium salts produced spontaneous emissions that darkened photographic plates.

  • Marie Curie (18671934) and her husband Pierre (18591906) took Becquerels mineral sample (called pitchblende) and isolated the components emitting the rays. The Discovery of Radioactivitydarkening of the photographic plates was due to rays emitted specifically from the uranium atoms present in the mineral sample.

  • The Discovery of RadioactivityMarie Curie named the process by which materials give off such rays radioactivitythe rays and particles emitted by a radioactive source are called radiation.

  • isotopes are atoms of the same element that have different numbers of neutrons.Types of RadiationIsotopes of atoms with unstable nuclei are called radioisotopesemit radiation to attain more stable atomic configurations in a process called radioactive decaylose energy by emitting one of several types of radiation.

  • Why do some atoms decay?The nucleus contains tightly packed protons and neutrons (nucleons)The strong nuclear force keeps the nucleons packed together even though protons want to push each other awayStable atoms have a neutron to proton ratio of about 1:1

  • As atomic number increases, more neutrons are required to have enough of a strong force to keep the protons pushed togetherThe neutron to proton ratio for stable atoms increases to 1.5:1

  • Band of StabilityWhen the number of protons and neutrons are plotted, the stable nuclei are found within the band of stabilityRadioactive isotopes are outside the band of stabilityThey will undergo nuclear reactions to become more stableAll elements higher than atomic# 83 are radioactive

  • Basic Assessment QuestionsExample 1Topic 26

  • Basic Assessment QuestionsAnswer1.6 : 1Topic 26

  • Types of Nuclear RadiationAlphaBetaGamma

  • Alpha RadiationRelease of 2 protons and 2 neutronsEquivalent to a He nucleusCharge of 2+Mass = 4 amuLargest and slowest Least penetrating can be stopped by paperChanges to a different element with a lower atomic mass and lower atomic numberExample: Polonium-212 (atomic# 84) is converted to Lead-208 (atomic# 82)

  • Beta RadiationDecay of a neutron into a proton and electronElectron is emitted, proton staysForms a new element b/c of addition of protonDecay of the proton into a neutron and positron (like a positive electron)The positron is emitted as a beta particleFaster than alpha particles can be stopped by aluminum foil

  • Gamma RadiationNot a particleElectromagnetic wave with short wavelength and high frequency & energyNo mass, no chargeVery fast speed of lightStronger than X-rayStopped by several centimeters of lead

  • Transmutation: changing one element into another through radioactive decayAdding or removing a proton changes the atomic number, resulting in a different elementHalf-Life: amount of time for half of a sample of a radioactive element to decay into something elseCan range from a fraction of a second to billions of yearsAmount remaining=initial amount(1/2)t/Tt=total timeT=half-life

  • Half-lifemf:final massmi:initial massn:# of half-lives

  • Half-lifeFluorine-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?