Make your own free website on

Lesson 2.2                                           Sept.29,30

Early Models of the Atom

1.  Greeks – philosophers, thinkers, ideas,

2.  Middle Ages – “Alchemy”

3.  Dalton (1800’s)

4.  Crooke/Thomson (1897)

5.  Millikan (1909)

6.  Becquerel (1896)

7.  Rutherford (1911)

8.  Chadwick/Curies (1932)





9.  Bohr Model

10.  Pauli, Heisenberg




The Bohr Model

Now that we have an atom with a positive nucleus made up of protons (p+)  and neutrons (n˚) the rest of the atom is mostly….


What else?

electrons traveling around at the speed of light (300,000 km/s)

Just what kind of pathways(orbit) do they travel?






What did Bohr say about the model of the atom?



- First he looked at the simplest element, H, because it had only one electron orbiting the nucleus

- He found that H gas,

 when energy(electricity) was passed through it under low pressure,

emitted , a unique light pattern.




- this light pattern could  be analyzed with a “spectroscope” and was found to contain certain frequencies (ν) related  to wavelength (λ).

(Heath p.282)







- How did he explain the unique spectrum?

To explain this, he proposed that the electron could occupy certain energy levels (discrete) and that when the electron got excited it absorbed energy… jumping up to a higher level.   

  Because the higher level was unstable, the electron quickly fell back to its original ground state.  The energy it had gained now was released or emitted!

(Planck, a physicist, had a formula E= )

So that E corresponded directly to a__frequency_.





If only certain frequencies were observed,

there must be certain chunks or QUANTA of energy….

and lead him to believe the electron could occupy only certain levels or orbits!


His lower orbit(ground state) was spherical.


Worksheets: pp. 1-3  q.1-7

1.  ability to explain… and predict

2.  no…theories are refined, improved,

3. law of conservation of matter- the mass of all the atoms in the reactants equals the mass of all the atoms in the products … they just rearrange themselves in new molecules(compounds)



4.  Dalton

☺-correctly predicted law of definite proportions (balanced reactions)

multiple proportions is the ratio of elements in compound

X- did not see sub-atomic particles causing the electrical nature of atoms


5.  Thomson

mass of atom is due mostly the protons

X – thought the positive charge was “uniformly” distributed.



6.  Rutherford

☺- neutrons and protons in the nucleus

atom mostly space, periodic table improved,

X – couldn’t explain possible collapse of atom


7. Bohr

☺ - correctly explained spectra by calculating the orbit of the 1 electron H atom,

X – orbits of multi-electron atoms are not circular or exact


8.  Quantum Mechanical Model

☺- Electrons are in energy levels described by mathematical probability equations.  They are more like waves. 















- Schroedinger

- Heisenberg


Watch the video and tell me how Bohr’s model was improved .