What was Niels Bohr's expanation for the observation of atomic spectra?

Answer 1

When a gas is excited in an electrical discharge, light is emitted (this is essentially how neon lamps work). Niels Bohr looked at this emitted light using a spectrograph, which separates different wavelengths of light (just a like a simple triangular prism). Atoms, such as hydrogen or neon, emit very specific patterns of light. When you separate the wavelengths, you see a pattern of very sharp lines of light at only certain wavelengths and not others. In other words, the atoms emit only certain wavelengths of light, resulting in a series of lines when you look at the light through a spectrograph. Bohr looked at these lines and managed to figure out the pattern that determined which wavelengths were observed. He said that the light emitted was due to transitions between energy levels in the atoms, and the wavelength of light corresponded to the energy difference between the two states involved in the transition. In this way, he figured out the equation to predict the spacing between all of the energy levels of any one-electron atom or ion. His model was quite successful, and he was able to predict which lines you would see for things that hadn't even been measured yet (a good test for any theory!). Surprisingly, although he figured out the pattern so well, he didn't actually know what the patterns were really due to. In fact, he had to make assumptions that turned out to be completely false! However, despite these errors (which were corrected when quantum mechanics was developed), the Bohr model of the atom is very useful for many applications. His model does NOT work well for multi-electron atoms/ions, which unfortunately includes the large majority of atoms and ions! You need quantum mechanics for that!

Answer 2

When electrons jump between discrete (i.e nothing in between) energy levels in an atom, they emit a photon of energy e = hf.

This value of e can only ever has a certain number of values (as proved in experiments), depending on which level the electron started in and jumped to.

If there were no discrete energy levels then there would be an infinite number of values.

Answer 3

any photon could excite an electron