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What is the energy state of electron?

  1. Mar 20, 2015 #1
    Can you please explain to me this statement The farther an electron is from the nucleus, the higher is the energy state, and any electron that has left its parent atom has a higher energy state than any electron in
    the atomic structure.
    And is the meaning of electron state.
  2. jcsd
  3. Mar 20, 2015 #2
    I'm not a specialist in quantum physics, but this link should be enough to get you started until somebody who is a specialist might want to contribute.


    Read the section about ground states and excited states in particular.
  4. Mar 21, 2015 #3
    When an electron is part of an atom, its energy cannot be anything, only certain values are allowed. A state is the set of numbers that describes an electron. Its energy is one of those numbers.

    When an atom absorbs a photon, an electron gains the energy by jumping from one energy state to another. Its average position around the nucleus is then further away from it.

    If the photon energy is sufficient, the electron flies off, and the atom is said to be "ionized" (until it meets up with another stray electron).
  5. Mar 21, 2015 #4


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    You can make an intuitive thought about it by observing the expectation values of kinetic energy and potential energy separately. The expectation value of kinetic energy must be positive, otherwise the momentum is not observable because it has complex value. Now a binding potential energy which is found in atoms or molecules is defined so that the most negative value of it is found near the potential source, in this case the nucleus. So if the wavefunction of a particular state is such that its probability distribution ## |\psi |^2 ## peaks at a farther distance from nucleus, the expectation value of potential energy will be more positive than a state whose probability to be found peaks at a closer distance. So the total energy becomes more positive as the probability distribution ## |\psi |^2 ## peaks at farther distances.

    A state is just the solution of time independent/dependent Schroedinger equation. It has no physical meaning until you take the modulus square of it to get the probability distribution/density. Nevertheless, in the language of measurement, a state can be thought of as the information carrier. When we measure the value of an observable (mathematically this means applying the corresponding operator of the observable to the wavefunction of the state), the outcome will be determined by the state of the system in that moment. Applying the same measurement to a different state might result different outcome.
    Last edited: Mar 21, 2015
  6. Mar 22, 2015 #5


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    It seems to me that this OP is about the definition of Potential Energy, more than QM. The fact that electrons around a nucleus can only have certain fixed levels of potential energy is important but not really relevant to the high or low description of the states.
    For an attractive situation, the potential energy is less than zero because Potential at a point is defined by 'the work needed to bring a charge from infinity to that point'. When the forces are attractive, clearly, work is got out so the work put in is negative.
    So. .. . at infinity, the potential is zero, which is higher than the potential of anywhere nearer (all negative values).
    However, with the inverse square law at work, the amount of energy available for a given change in position is greater, the nearer you get (the 'well' is steeper near the centre. It is potential difference that is of most interest, in many cases and the absolute potential is not very relevant. Getting ones head around this can be difficult but it does make sense - really!
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