intro to nuclear chemistry december 12

Download Intro to Nuclear Chemistry DECEMBER 12

Post on 16-Jan-2016




1 download

Embed Size (px)


  • Intro to Nuclear Chemistry


  • How does a nuclear reactor work?

  • How does a small mass contained in this bomb causeNuclear Bomb of 1945 known as fat man

  • this huge nuclear explosion?

  • Is there radon in your basement?

  • Notation

  • NucleonsProtons and Neutrons

  • The nucleons are bound together by a strong force called binding force.

  • IsotopesAtoms of a given element with: same #protons but different # neutrons

  • H H H

  • Isotopes of Carbon

  • Isotopes of certain unstable elements that spontaneously emit particles and energy from the nucleus.

    Henri Beckerel 1896 accidentally observed radioactivity of uranium salts that were fogging photographic film.

    His associates were Marie and Pierre Curie.

    Radioactive Isotopes

  • Marie Curie: born 1867, in Poland as Maria SklodowskaLived in France1898 discovered the elements polonium and radium.

  • Marie Curie a Pioneer of RadioactivityWinner of 1903 Nobel Prize for Physics with Henri Becquerel and her husband, Pierre Curie. Winner of the sole 1911 Nobel Prize for Chemistry.


    Emission of rays and particles from unstable nuclei.When a nucleus is emitting rays or particles it is said that is DECAYING or is disintegrating.

  • Stability of nuclei:

    Depend on the ratio between the neutrons and protons. Too many or too few neutrons lead to an unstable nucleus. All elements with more than 83 protons are unstable.

  • Transmutation

    When the nucleus of one element is changed into the nucleus of another element. IT CAN ONLY HAPPEN IN A NUCLEAR REACTION!!!

  • Nuclear ReactionsThe chemical properties of the nucleus are independent of the state of chemical combination of the atom.In writing nuclear equations we are not concerned with the chemical form of the atom in which the nucleus resides.It makes no difference if the atom is as an element or a compound.Mass and charges MUST BE BALANCED!!!

  • Types ofRadioactive Decay

  • SeparationAlphaBetaGamma.MOV Separation of Radiation

  • Emission of alpha particles a :

    helium nuclei two protons and two neutrons charge +2e can travel a few inches through aircan be stopped by a sheet of paper, clothing.Alpha Decay

  • Alpha DecayUranium Thorium

  • Alpha Decay

  • Alpha Decay:Loss of an -particle (a helium nucleus)

  • Alpha DecayMass changes by 4The remaining fragment has 2 less protonsAlpha radiation is the less penetrating of all the nuclear radiation (it is the most massive one!)

  • Alpha decay:

    When a nucleus emits alpha particles.* Atomic number decreases by 2.* Mass number decreases by 4.* Neutrons decrease by 2.

  • Beta Decay:Loss of a -particle (a high energy electron)

  • Beta Decay

    Beta particles b: electrons ejected from the nucleus when neutrons decay( n -> p+ +b- ) Beta particles have the same charge and mass as "normal" electrons.

  • Beta DecayBeta particles b: electrons ejected from the nucleus when neutrons decay n -> p+ +b- Beta particles have the same charge and mass as "normal" electrons.

    Can be stopped by aluminum foil or a block of wood.

  • Beta Decay

    When a neutron becomes a proton and emits an electron.* Atomic Number or number of protons increases by 1* Number of neutrons decreases by one.* Mass number remains the same.

  • Beta Decay

  • Beta DecayThorium Protactinium

  • Beta DecayInvolves the conversion of a neutron in the nucleus into a proton and an electron.Beta radiation has high energies, can travel up to 300 cm in air.Can penetrate the skin

  • Beta decayWrite the reaction of decay for C-14

  • Positron Emission

    When a proton changes to a neutron emits a positron.*Atomic number (number of protons)decreases by 1*Number of neutrons increase by 1.*Mass number remains same

  • Gamma Emission:Loss of a -ray (high-energy radiation that almost always accompanies the loss of a nuclear particle)

  • Gamma radiation g : electromagnetic energy that is released.Gamma rays are electromagnetic waves.They have no mass.Gamma radiation has no charge. Most Penetrating, can be stopped by 1m thick concrete or a several cm thick sheet of lead.

    Gamma Decay

  • 3 Main Types of Radioactive DecayAlpha a

    Beta b

    Gamma g

  • Examples of Radioactive DecayAlpha DecayPo Pb + He

    Beta Decay p n + en p + e C N + eGamma DecayNi Ni + g(excited nucleus)

  • Which is more penetrating? Why?

  • December 14Nuclear stability Half life

    HW review bookQuestion 34 to 47

  • Nuclear StabilityDepends on the neutron to proton ratio.

  • Band of StabilityNumber of Neutrons, (N)Number of Protons (Z)

  • What happens to an unstable nucleus?They will undergo decay

    The type of decay depends on the reason for the instability

  • What type of decay will happen if the nucleus contains too many neutrons?Beta Decay

  • Example:C N + e

    In N-14 the ratio of neutrons to protons is 1:1147-10146

  • Nuclei with atomic number > 83 are radioactive

  • Radioactive Half-Life (t1/2 ): The time required for one half of the nuclei in a given sample to decay.After each half life the mass of sample remaining is half.Different Isotopes have different half lives. Use table N

  • Common Radioactive IsotopesIsotope Half-Life Radiation Emitted

    Carbon-14 5,730 years b, g

    Radon-222 3.8 daysa

    Uranium-235 7.0 x 108 years a, g

    Uranium-238 4.46 x 109 years a

  • Radioactive Half-LifeAfter one half life there is 1/2 of original sample left.

    After two half-lives, there will be 1/2 of the 1/2 = 1/4 the original sample.

  • Graph of Amount of Remaining Nuclei vs TimeA=Aoe-ltA

  • ExampleYou have 100 g of radioactive C-14. The half-life of C-14 is 5730 years. How many grams are left after one half-life? Answer:50 g How many grams are left after two half-lives?

  • ProblemIf 80 g of a radioactive sample decays to 10 g in 30 min what is the elements half life?

  • How many days will take a sample of I-131 to undergo three half life periods?

  • What is the total mass of Rn-222 remaining in an original mass 160 mg sample of Rn-222 after 19.1 days?

  • Measuring RadioactivityOne can use a device like this Geiger counter to measure the amount of activity present in a radioactive sample.The ionizing radiation creates ions, which conduct a current that is detected by the instrument.

  • TransmutationsTo change one element into another.Only possible in nuclear reactions never in a chemical reaction.In order to modify the nucleus huge amount of energy are involved.These reactions are carried in particle accelerators or in nuclear reactors

  • Nuclear transmutationsAlpha particles have to move very fast to overcame electrostatic repulsions between them and the nucleus.Particle accelerators or smashers are used. They use magnetic fields to accelerate the particles.

  • Particle Accelerators(only for charged particles!)These particle accelerators are enormous, having circular tracks with radii that are miles long.

  • CyclotronNuclear transformations can be induced by accelerating a particle and colliding it with the nuclide.

  • NeutronsCan not be accelerated. They do not need it either (no charge!).Neutrons are products of natural decay, natural radioactive materials or are expelled of an artificial transmutation.Some neutron capture reactions are carried out in nuclear reactors where nuclei can be bombarded with neutrons.

  • Mass defectThe mass of the nucleus is always smaller than the masses of the individual particles added up.The difference is the mass defect.That small amount translate to huge amounts of energy E = (m) c2That energy is the Binding energy of the nucleus, and is the energy needed to separate the nucleus.

  • Energy in Nuclear ReactionsFor example, the mass change for the decay of 1 mol of uranium-238 is 0.0046 g.The change in energy, E, is thenE = (m) c2E = (4.6 106 kg)(3.00 108 m/s)2E = 4.1 1011 J This amount is 50,000 times greater than the combustion of 1 mol of CH4

  • Types of nuclear reactionsfission and fusionThe larger the binding energies, the more stable the nucleus is toward decomposition.Heavy nuclei gain stability (and give off energy) if they are fragmented into smaller nuclei. (FISSION)

  • Even greater amounts of energy are released if very light nuclei are combined or fused together. (FUSION)

  • Nuclear FissionNuclear fission is the type of reaction carried out in nuclear reactors.

  • Nuclear FissionBombardment of the radioactive nuclide with a neutron starts the process.Neutrons released in the transmutation strike other n