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Nuclear Physics. The atom and its nucleus. Discovery of the nuclear atom. 1909-Geiger and Marsden, working under Rutherford Scattering of alpha particles shot at a thin gold foil Alpha particle 4x mass of H atom Alpha particles-emitted when unstable elements decay

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Nuclear physics

Nuclear Physics

The atom and its nucleus


Discovery of the nuclear atom
Discovery of the nuclear atom

  • 1909-Geiger and Marsden, working under Rutherford

    • Scattering of alpha particles shot at a thin gold foil

    • Alpha particle 4x mass of H atom

    • Alpha particles-emitted when unstable elements decay

    • Used radon – source of alpha particle


Rutherford geiger and marsden
Rutherford, Geiger, and Marsden

  • Found that sometimes alpha particles were detected at very large scattering angles

  • This couldn’t be understood in terms of the prevailing model

    • Thomson


Geiger marsden rutherford experiment
Geiger-Marsden-Rutherford experiment

  • Deflection indicative of enormous force of repulsion between alpha particle and carrier of positive charge of atom

  • Positive charge resided on a tiny object

  • Alpha particle could approach + charge at a small d, and the Coulomb force of repulsion, would be enormous


Rutherford model
Rutherford model

  • Massive, positively charged nucleus

  • Electrons orbited nucleus

  • Force keeping electrons in orbit

    • Electrical force between negative electron charge and positive nuclear charge

  • Couldn’t explain why matter is stable, i.e. why atoms exist


Bohr model
Bohr model

  • Examined hydrogen

    • Realized electron could exist in certain specific states of definite energy, without radiating away energy

  • Electron lose energy when makes transition from one state to a lower

  • Emitted energy is difference between states

  • Evidence-emission and absorption spectra


Spectra
Spectra

  • Normal conditions-lowest energy level

  • Atoms excited  higher level

  • As soon as they do, transition back down to lower state

  • Energy allows wavelength of emitted light to be calculated


Spectra1
Spectra

  • Emission spectrum  set of wavelengths of light emitted by the atoms of an element

  • Send a light of specific wavelength through an atom

    • Doesn’t correspond to any of the wavelengths

    • Light transmitted without absorption


Nuclear structure
Nuclear Structure

  • Protons and neutrons

  • # of protons is Z (atomic number)

  • Protons + neutrons = mass (A)

  • Electric charge is Z IeI

  • # of neutrons N= A-Z

  • Nucleon

    • Proton or neutron


Isotopes
Isotopes

  • Nuclei that have the same number of protons, but different number of neutrons

  • Same number of electrons

  • Identical chemical properties, different physical

  • Mass spectrometer


Forces within the nucleus
Forces within the nucleus

  • Nucleons bound by nuclear force

    • Attractive force

    • Stronger than electrical force if separation between 2 nucleons is small

    • Larger separation-small force

  • Nuclear radius

    • R = 1.2 A1/3 x 10-15m

    • A is total number of p and n


Forces within the nucleus1
Forces within the nucleus

  • Weak nuclear force

    • Responsible for decay of a neutron into a proton

    • Called beta decay