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Ionization Energy QNS

  1. Jul 5, 2013 #1


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    Hi, I am slightly confused with the term, ionization energy (IE). I am stuck between two definitions, one is the minimum energy to remove an outermost electron from an atom while the other is the energy to completely remove an electron from ground state.

    If its the former, wouldn't it have a higher potential energy than that of the ground state, thus lower IE? Coz I understand that the ionization energy refers to 0-(-energy at ground state).

    Thanks in advance!
  2. jcsd
  3. Jul 5, 2013 #2


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    Staff: Mentor

    As far as I know, the first definition is correct. Where did you read the second definition?

    The two definitions are the same for a one-electron atom (hydrogen), of course. Did the second definition appear in the context of a discussion about hydrogen?
  4. Jul 5, 2013 #3


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    The exact definition was like this "The energy level of the ground state gives the ionization energy, i.e. the energy needed to completely remove an electron initially in the ground state from the atom {i.e. to the energy level n = āˆž, where Eāˆž =0}".
    Got it from this site :http://www.xtremepapers.com/revision/a-level/physics/quantum_physics.php

    On a side note, am I right to say that the production of a continuous x ray spectrum is due to breaking radiation whereby electrons accelerated towards target material loses its entire KE to emit photons? As for the characteristics of x ray, it is due to electrons being removed by the incoming electrons which led to a transition of electrons from higher energy level to the vacant energy level, emitting photons.
  5. Jul 5, 2013 #4


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    Science Advisor

    strictly speaking, any energy difference between the molecule in a N-electron ground state and the molecule in a N-1 electron eigenstate can be called an ionization energy. That is, in generay there is more than one of them, often they correspond roughly to removing an electron from a canonical orbital.

    If someone talks about "the" ionization energy, she means the difference between the ground state energy and the lowest energy N-1 electron state (i.e., the lowest ionization energy).

    Additional complications can arise in the case of molecules, where also vibrational contributions to the ionization energy exist, and where ionized states and non-ionized states have different geometries. One then speaks of either vertical ionization energies (where the N-1 electron state is considered in the molecular geometry of the ground state) or adiabatic ionization energies (where the molecular geometry is relaxed in the N-1 electron state)
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