Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Velocity of electrons

  1. Oct 7, 2008 #1
    hello, this is my first post here. I am new not only to this site, but to quantum physics in general. this might be a 'dumb' question, but scouring the internet has not given me any useful answers. I have read that the position of an electron is 'erratic', so does a hydrogen atom have a frequency/ wavelength? If so, does it oscillate constantly? how could I determine the low/ high points on a hydrogen atom's wavelength when the electron is at ground state (i think thats the right terminology.. energy level 1 perhaps?). Is the radiation frequency related in any way to the natural frequencies of the atom? i guess that is enough for one sitting.

    if anyone has an idea of where i can go to find this information, pointing me in the right direction would be very much appreciated! thank you in advance,

  2. jcsd
  3. Oct 7, 2008 #2
    The position of an electron can't be determined until you look at it. You could almost say it's orbiting the hydrogen atom, but it's really not. It's really everywhere at once until you try and find it at a specific point.

    Read up on de Broglie wavelength. Basically everything is both a particle and a wave, so everything has a wavelength, even a hydrogen atom or a basketball. So the electron is within its de Broglie wavelength of the proton in a hydrogen atom. And until you try and poke it, you can't tell where it is.

    The thing is the wavelength is so tiny that on "classical" (i.e. big scale) levels we don't even know about it. But, if you get particles close enough together that their de Broglie wavelengths overlap (even partially), you get quantum effects.

    Frequency as far as I know for particles with mass is pretty meaningless. f = v/lambda, but the frequency doesn't work into anything that I know of. The wavelength is the only thing that matters.

    No, the radiation frequency is only related to jumps in energy levels of electrons. If an electron jumps from the 1st excited state of the Hydrogen atom back down to the ground state, it emits 1 photon with E = h*f. So the energy of the jump is something that is well known and doesn't change, and h is a constant, so you get light of frequency f from that.
  4. Oct 7, 2008 #3
    thanks for responding! i actually just looked up de brogile today. but i thought that c=[tex]\lambda[/tex] X [tex]\upsilon[/tex] so atoms have a frequency depending on the wavelength. does the wavelength oscillate?
  5. Oct 8, 2008 #4
    You can look up references to the Bohr Model and Rydberg constant such as:


    The calculations Bohr developed for radiation wavelengths of the Hydrogen atom are quite accurate.
  6. Oct 8, 2008 #5
    thank you for posting philDSP. i have researched the bohr model, but that is an approximation. it can not tell you what it is at ground state.
  7. Oct 9, 2008 #6


    User Avatar
    Gold Member

    I was a little confused by your use of 'it' and I may not be quite sure what you mean. Regarding the velocity of electrons, visualize a hydrogen proton as being a shell with a Bohr radius of 53 picometers (commonly shown this way in chemistry books) and a slow passing electron (say 100 picometers away) being pulled into the proton by the coulomb force.

    If you measure it, the electron will be going about 2 picometers/attosecond when it enters the shell at 53 picometer distance from the center of the proton. A short time later, the electron will emerge from the other side of the proton shell going about 2 picometers/attosecond. In contrast, the speed of light is about 300 picometers/attosecond. In the normal world of chemistry, the electron is not going fast enough and we are not trying to measure its position accuracy to such a degree that uncertainty would come into play.

    I think its reasonable to say in the normal world around us, electrons are buzzing around mostly in the range of 0 to 2 picometers/attosecond.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook