What is Thompson’s model of atom?
Positive charge sphere with negative charges at various locations within
What was was Ernst Rutherford’s change of the atom?
Designed experiment done by his students where a thin gold foil was bombarded by alpha particles and found some alpha particles deflected through large angles
Proposed most of a
Mass and all positive charge is concentrated at nucleus
Slides 23-27 March 26
What is atomic spectra?
If a tube is filled with a gas at low pressure, and an applied voltage is great enough to produce an electric current in the gas, the tube emits light having a colour that is characteristic of the gas
Low pressure ensures that any effects are due to individual atoms, not the collective behaviour of the atoms
Characteristic colour corresponds to a set of discrete wavelengths
Slides 28-32 March 26
What is the absorption spectra?
If a continuous radiation spectrum is passed through a vapour of an element, the atoms in the vapour will absorb the wavelengths corresponding to the discrete wavelengths that the vapour atoms emit
The appearance of various elements in the atmosphere of the sun was determined by the appearance of absorption lines in light from the sun
Slides 33-36 March 26
What is the Bohr model of the atom?
Combined Rutherford nuclear model with the quantum ideas of Planck and Einstein
Electron moves circular orbit around the proton (Coulomb force produces the centripetal acceleration)
Only certain electron orbits allowed
Electron can transition from one allowed orbit to another by emitting it absorbing a photon of appropriate energy
KE= 1/2 (ke)(e)^2 / r
Slides 2-5 March 28
How to find the Bohr orbit radii?
Slides 6-9 March 28
Apply angular momentum quantization condition allows elimination of the electron speed in equation 1 and gives predicted values of the orbit radii
As energy of photon goes up, what does eV do?
Slide 9 March 28
Energy goes up, eV goes down
What is the origin of line spectra?
Because the electron energies are quantized, so are the energies of the photons emitted when an electron makes a transition between allowed states
Ephoton=Ei-Ef
hc/λ=-13.6eV(1/ni^2 - 1/nf^2)
What are hydrogen like atoms?
An atom is hydrogen like if it has only one electron
The Bohr equations apply, with the substitution of Ze for e
E= me(ke^2)(Z^2)(e^4)/2h^2 (1/n^2)
=-13.6Z^2/n^2 eV
Slide 12 March 28
What are the problems with the Bohr model?
Classical physics does not apply at the atomic level
Proper explanation of the atom involves quantum mechanics and deals with the probability of the electron being at various distances from the nucleus
Bohr model does not address the probability of an electron absorbing or emitting a photon
