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

Ionization and electron affinity

  1. Jul 16, 2015 #1
    I am confused about Ionization and electron affinity concept

    If energy is Required to add the electron to gaseous atom (Electron affinity - in case of noble gases) Then why further energy is required to Remove it? (Ionization energy)
    isnt this violation of Conservation of energy?
     
  2. jcsd
  3. Jul 17, 2015 #2

    DrDu

    User Avatar
    Science Advisor

    The energy for the addition of an electron to a neutra gas atom and that for the removal of an electron from an anion are of equal absolute value but opposite sign.
    However there is much confusion as the tabulated electron affinity often refers to the second formulation, i.e. the energy required to remove an electron from an anion.
    So you must be very careful about which convention is used in the table of data you are consulting.
     
  4. Jul 17, 2015 #3
    sorry My question is : (leaving the sign conventions aside)
    If energy is Required to add the electron to gaseous atom (Electron affinity) Then why further energy is required to Remove it? ( infact it should release the energy)
     
  5. Jul 17, 2015 #4

    DrDu

    User Avatar
    Science Advisor

    You are completely right. Who claimed the opposite?
     
  6. Jul 17, 2015 #5
    Thank you for reply.
    Well, it is well known fact that Ionization energy (second case) is always positive I.e Energy is required to Remove the electron.

    (electron gain enthalpy can be negative or positive, but Ionization enthalpy is always positive)
     
  7. Jul 17, 2015 #6

    DrDu

    User Avatar
    Science Advisor

    That's only true for the ionization of neutral atoms, not for the ionization of anions.
     
  8. Jul 17, 2015 #7
    So it means , In case anions, IE is negative ?

    I cant find any link favouring that statement ? Can you give me any source ?
     
  9. Jul 17, 2015 #8

    DrDu

    User Avatar
    Science Advisor

    https://en.wikipedia.org/wiki/Ionization_energy
    sais
    "The ionization energy (IE), (or "ionization potential" - not recommended),[1] is qualitatively defined as the amount of energy required to remove an electron from an atom or molecule in the gaseous state."
    So the term ionization energy usually refers to the ionization of a neutral atom or molecule, not an anion. This is also what I remember.
     
  10. Jul 17, 2015 #9
    2nd Ionization enthalpy........... is actually removing electron from the ION.

    infact all the successive Ionization energies are for Removing electrons from Ions.
     
    Last edited: Jul 17, 2015
  11. Jul 17, 2015 #10

    DrDu

    User Avatar
    Science Advisor

    That's why they are explicitly called second IEs.
     
  12. Jul 17, 2015 #11
    If X is neutral :

    X + e- + E.A. -----> X- : E.A. is the electron affinity.
    X+ I. E. ---> X+ + e- : I.E. Ionization energy
    X+ + 2nd I.E. -----> X2+ + e-
     
  13. Jul 17, 2015 #12
    Thank you very much ...... It makes sense now.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Ionization and electron affinity
Loading...