Atomic Model Development

Plum Pudding model
- Thomson
Rutherford Model
- limitation
  - Electrons moving in a circular orbit
  - Charged particles being constantly accelerated; meaning that electrons should continuously emit emr, lose energy and spiral into nucleus
Bohrs Model
- Improvements from Rutherford Model that Bohr needed to explain
  - Why emission spectra consisted of lines
  - Why the visible spectrum, fitted the Balmer equation the way it did
  - Why you got similar patterns of lines from hydrogen in the UV and IR
  - it needed to incorporate Planck’s quantum hypothesis
  - He synthesised these into a new model
- Several Postulates
  - circular orbits around the nucleus
  - There are only certain orbits (stable orbits or stationary states or energy levels) that an electron can occupy and not radiate energy
  - The condition for these stable orbits is that these orbits occur when the angular momentum of the electron is equal to a whole number multiple of a constant $\frac{h}{2\pi}$. Angular momentum is equal to linear momentum x radius (=mvr). In other words, the angular momentum is quantised
  - Electrons can move from one stable orbit to another by emitting or absorbing a quanta of electromagnetic radiation (energy). The frequency of the radiation is determined by the difference in energy levels according to (E=hf)
- Limitations
  - Relative Intensity of the spectral lines
    - Some lines are brighter than others; This means that more photons are emitted of some wavelengths
    - Some electron transitions occur more often than others
  - All electrons transfer between shells release the same wavelength and energy
  - Hyperfine spectral lines
    - There are two red lines spaced very closely together
    - Most single lines are actually several fine lines
  - Zeeman Effect
    - Putting a very strong magnetic field through the gas, the single spectral lines split into several lines
  - Cannot accurately predict the lines in other atoms with more than 1 electron
  - More theoretical/philosphical limitation
    - Mixture of classical and quantum physics
  - it was completely experimental, and couldn't be concluded through math
- It was a big step for the atomic model, and worked out a lot of the broad detail
de Broglie
- suggested electrons had wave properties
- changed the perception of what electrons are
- Schrödinger fully developed quantum mechanics; changed our understanding of electrons and atoms
- Hypothesis
  - Einstein and Planck showed that light had particle properties as well as wave properties (Photons)
  - De Broglie proposed that maybe particles have
- Conclusion
  - For large objects, the de Broglie wavelength is insignificant
  - atomic objects, the wave is significant
  - This means when dealing with electrons in atoms, they must be treated as waves
  - De Broglie then went on to suggest that the stable orbits of electrons only occur when the electron wave forms a standing wave
  - De Broglie used this hypothesis to calculate the radii of the stable orbits in the hydrogen atom, and got the same values as bohr