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

The ground state e- is the largest negative value, but why?

  1. Feb 9, 2015 #1
    Hi Physics Forums!

    The ground state electron is the largest negative value, but what does this mean?

    Does this mean that kinetic energy is a positive value above zero?

    It seems at the ground state, the electron might also have kinetic energy as it is moving around as well as potential energy....

    It seems like the scientists, when they talked about the lowest ground state, meant lowest potential energy similar to that of gravitational potential energy.

    I'm trying to see this in terms of kinetic energy and potential energy, especially when we excite the electron with kinetic energy.

    A: I think that when we excite the electron, the electron was at it's quantized potential energy, and then turns into kinetic energy, and drops back down to potential energy.

    I was also confused on how we measure the electron volts, or potential energy of a ground state electron?
  2. jcsd
  3. Feb 10, 2015 #2


    User Avatar
    Science Advisor
    Gold Member

    An electron in its ground state has the lowest possible value for its total energy. That total energy can be negative, as it might be in the ground state of an atom, in which case, we could say that the energy of an electron in its ground state is at its "most negative".

    The kinetic energy of an electron when measured will always have some value greater than zero. The potential energy can be negative, depending on what the potential energy function is.

    The total energy (kinetic plus potential) is what's quantized for an electron in an atom. When an electron absorbs a photon, its total energy increases by the amount of the energy of the absorbed photon,

    An electron-volt is the amount of energy an electron gains when it moves to a location where the electric potential is one volt lower than where it started.

    To measure the energy levels of electrons in atoms, we shine light at known frequencies at it, and see how the atoms respond to the light. Since the energy of a photon is directly proportional to its frequency by Planck's constant, we can figure out what the energy differences between the energy levels of an atom are by knowing which frequencies the atom interacts with most strongly.

    Hope this helps :)
  4. Feb 10, 2015 #3


    User Avatar
    Science Advisor

  5. Feb 10, 2015 #4


    User Avatar

    Staff: Mentor

    That's generally not a helpful way of understanding a bound electron. The problem is that the energy eigenstates of a bound electron are not position eigenstates; the electron has no single definite position in these states. The potential ##V(r)## is a function of the position, so the electron also has no definite potential energy in these states. Thus, there is no useful way of splitting the total energy (which does have a definite value) into potential and kinetic components; all you have a statistical distribution of what you would get if you were to somehow measure one or the other.
  6. Feb 11, 2015 #5
    Thank you everyone! This makes a lot more sense now. Phew. Physics is so weird!
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook