Hydrogen's emission spectrum has four colored lines. Since H has only one electron, this would seem impossible. How is it possible for hydrogen's emission spectrum to have four lines, when hydrogen has only one electron?
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Electrons can occupy different energy levels. When an electron goes from a high energy to a low energy level, it gives off the extra energy as a photon. This photon has a certain wavelength depending on the difference in energy of the levels.
There may only be one electron, but it can go to any of those energy levels and then drop down and emit a photon.
There may only be one electron, but it can go to any of those energy levels and then drop down and emit a photon.
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Visible light is produced when excited electrons fall from a higher energy level to the 2nd energy level. The greater the drop (7 --->2) the closer to the violet end of the spectrum the emitted light is; the smaller the drop (3 ---> 2) the closer to the red end of the spectrum the emitted light is. The drop from the 7th energy level is not that much more energy than a drop from the 6th energy level. The light produced may be too similar in wavelength to 'look' like a different color. Electrons falling from (7&6), 5, 4, 3 to energy level 2 would produce only 4 lines (one for each possible drop).
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Because that electron can "jump" to four different energy levels.