Early Atomic Models Dalton, Thomson, Bohr, Rutherford

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  • Early Atomic ModelsDalton, Thomson, Bohr, Rutherford

  • Thomson ModelJJ Thomson obviously knew about Daltons atomic theory when he discovered the electron and characterized the proton that was first observed by Goldstein. Thomson took this information and developed a model of the atom

  • Thomson ModelCathode Ray ExperimentDesigned to test emissions from metalCathode emits raysAnode receives rays

    Click the picture to run movie

  • Thomson ModelThis model became known as the plum-pudding modelThis model said that the atom was a diffuse positive charge and the electrons were randomly scattered throughout the atom.

  • Thomson ModelIn the picture, the blue region is the diffuse positive charge and the red spheres represent the electrons randomly placed in the atom.eeeeePositively charged spaceElectrons

  • Rutherford Au Foil ExptErnest Rutherford developed an experiment that would help to reveal the structure and location of the subatomic particles in the atom.This experiment was proposed by Rutherford and carried out by two of his graduate students: Geiger and Marsden.Became known as Rutherford Gold Foil Expt.

  • http://www.sci.tamucc.edu/pals/morvant/genchem/atomic/page7.htm

  • Two different modelsWhich one is right?Thomson ModelAu foil experiment should either allow all of the alpha particles (He2+) to pass through untouched (inconsistent with the nature of solidsshould be tightly packed positively charged spheres) or allow no alpha particles to pass through which would be consistent w/ a solid.Rutherford ModelUnsure of what to expect. Need to determine the internal structure of the atom. The scattering pattern of the alpha particles would help indicate the atomic structure.

  • Rutherford Au Foil Expt AppletThis applet illustrates what they saw.http://micro.magnet.fsu.edu/electromag/java/rutherford/

  • Rutherford AtomAll positive charge of atom was in nucleusEssentially all mass was in the nucleus

  • Rutherford ModelThe Au Foil Expt proved several things about the structure of the atom:All of the positive charge of the atom resides in a very small part of the atomwe call this the nucleus.The nucleus occupies a very small part of the atoms total volume (only
  • Niels BohrBohr was aware of different spectra for different elementsHydrogen was postulated to be the simplest of all substances because it had the lightest mass.He concentrated on hydrogens spectrum

  • Bohr AtomBohr postulated that the light that was seen in the spectrum was due to electron transitions.We call this model of the atom the solar system model of the atom.

  • Bohr AtomIn order to explain discrete spectra, Bohr found that atoms obey three basic rules: Electrons have only certain energies corresponding to particular distances from nucleus. As long as the electron is in one of those energy orbits, it will not lose or absorb any energy. The energy orbits are analogous to rungs on a ladder: electrons can be only on rungs of the ladder and not in between rungs. The orbits closer to the nucleus have lower energy. Atoms want to be in the lowest possible energy state called the ground state (all electrons as close to the nucleus as possible).

  • Bohr AtomEnergy LevelsNucleus

  • Erwin SchrdingerAdded orbitals (s, p, d, f) to Bohrs energy levelsThe orbital paths created an electron cloud that looks fuzzy, rather that distinct orbits precisely on the surface of spheresThe orbitals allow the electrons to avoid each other, which is necessary as they are all negatively chargedHe did this through some very rigorous mathematical description of the electrons in the atom.


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