nuclear chemistry the discovery of radiation nuclear reactions are different from other types of...

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  • Nuclear Chemistry

  • The Discovery of RadiationNuclear reactions are different from other types of reactions.Nuclear chemistry is concerned with the structure of atomic nuclei and the changes they undergo.Wilhelm Roentgen discovered x-rays in 1895.Marie Curie and her husband Pierre isolated the first radioactive materials.

  • Nuclear ReactionsNuclear reactions are different from other types of reactions.Involve changes in the nucleus of the atomprotons (p+) and neutrons (n)The location of the atom (which compound it is in) has no effect

  • Differences from Chemical reactionsUnaffected by changes in conditions temperature and pressureSpeed of reaction cannot be changedActuarial tablesMass is not conserved

  • RadioactivityThe process where the nucleus of an atom undergoes changes and releases energy, particles, or both

  • RadioisotopesIsotopes of an element that are radioactive due to unstable nucleiUndergo radioactive decayNucleus falls apart, not grows largerUnstable nuclei emit radiation to attain more stable atomic configurations

  • RadioactivityWhy do radioisotopes emit radiation? A.to balance charges in the nucleus B.to release energy C.to attain more stable atomic configurations D.to gain energy

  • Types of radiationAlpha particlesBeta particlesGamma radiationPositron emission at times

  • Types of RadiationThe ability of radiation to pass through matter is called its penetrating power.Gamma rays (like x-rays) are highly penetrating because they have no charge and no mass.

  • Alpha particlesSymbolized as:42He42Charge of +2Mass ~4 amuHeaviest of the particles

  • Types of Radiation Alpha radiation is not very penetratinga single sheet of paper will stop an alpha particle.

  • Beta particlesSymbolized as0-1e-O-1 Charge of -1Mass ~ 0.00055amuActually an electron emitted from the nucleus

  • Types of RadiationBeta radiation is a stream of fast moving particles with greater penetrating powera thin sheet of foil will stop them.

  • Gamma radiationNot a particleHigh energy electromagnetic radiation (light)Also known as a type of photonSymbolized as No charge, no mass

  • NeutrinoSymbolized as 00Have no charge and extremely little massCarry energy away from the reaction Hypothesized to exist to explain the wide variance of energy released in some nuclear reactions

  • X rays are most similar to what type of nuclear emissions? A.gamma rays B.alpha particles C.beta particles D.delta waves

  • Nuclear reactionsThe total of all the mass numbers of the reactants equals the total of all the mass numbers of the productsThe same holds true for the atomic numbersActual mass is not conservedMatter is transformed into energy

  • Symbols in nuclear reactionsAlpha particle42He or 42Beta particle0-1e or 0-1Gamma radiation00Neutrino00

    Proton11p+ or 11HNeutron10noElectron0-1ePositrons0+1e

  • Writing Nuclear reactions1) The nuclide that decays is the one on the left-hand side of the equation.2) The order of the nuclides on the right-hand side can be in any order.3) The neutrino symbol is the Greek letter "nu." 004) The mass number and atomic number of a neutrino are zero.

  • Alpha ( ) Decay1) The nucleus of an atom splits into two parts.2) One of these parts (the alpha particle) goes zooming off into space.3) The nucleus left behind has its atomic number reduced by 2 and its mass number reduced by 4 (that is, by 2 protons and 2 neutrons).

  • Types of Radiation Alpha radiation is not very penetratinga single sheet of paper will stop an alpha particle.

  • Alpha ( ) Decay

  • Beta ( ) Decay1) A neutron inside the nucleus of an atom breaks down, changing into a proton.2) It emits an electron and an anti-neutrino which go zooming off into space.3) The atomic number goes UP by one and mass number remains unchanged.

  • Types of RadiationBeta radiation is a stream of fast moving particles with greater penetrating powera thin sheet of foil will stop them.

  • Beta ( ) Decay

  • Types of Radioactive Decay (cont.)

  • Positron (01+e) Emission1) Something inside the nucleus of an atom breaks down, which causes a proton to become a neutron.2) It emits a positron and a neutrino which go zooming off into space.3) The atomic number goes DOWN by one and mass number remains unchanged.

  • Positron (01+e) Emission

  • Electron CaptureElectron capture is not like any other decay - alpha, beta, or position. All other decays shoot something out of the nucleus. In electron capture, something ENTERS the nucleus

  • Electron Capture1) An electron from the closest energy level falls into the nucleus, which causes a proton to become a neutron.2) A neutrino is emitted from the nucleus.3) Another electron falls into the empty space in the electron cloud and so on causing a cascade of electrons falling. 4) The atomic number goes DOWN by one and mass number remains unchanged.

  • Writing electron capture equations1) The nuclide that decays is the one on the left-hand side of the equation.2) The electron must also be written on the left-hand side.3) A neutrino is involved , It is ejected from the nucleus where the electron reacts, so it is written on the right-hand side.

  • Electron Capture

  • Types of Radioactive Decay (cont.)

  • Nuclear Chemistry

  • What causes nuclear instability?The wrong number of neutronsAtoms 1 20, p+ to no ratio is ~ 1:1Atoms 21 and up, the ratio approaches 1:1.5

  • Nuclear Stability (cont.)The strong nuclear force acts on subatomic particles that are extremely close together and overcomes the electrostatic repulsion among protons.

  • Nuclear Stability (cont.)As atomic number increases, more and more neutrons are needed to produce a strong nuclear force that is sufficient to balance the electrostatic repulsion between protons.Proton to neutron ratio increases gradually to about 1:1.5

  • What if there are too many protons and neutrons?Lose some of bothAlpha emission (42)Remember- an alpha particle is two protons and two neutronsMass number goes down by 4 atomic number goes down by 2

  • What if there are too many n0?Convert a no into a p+Beta emissionMass number stays the same, but atomic number goes up by 1

  • What if there are too few no?Either 1) Positron emission: Convert a proton into a neutron158O 157N + 01+e + 00

    or 2) e- capture: A proton merges with an electron to become a neutronBoth: #p+ by 1 and #n0 by 1

  • Credits.Portions of this presentation were adapted from the ChemTeam website

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