Ionization and electron affinity

[harman90]

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?

 

[DrDu]

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.

 

[harman90]

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)

 

[DrDu]

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)

You are completely right. Who claimed the opposite?

 

[harman90]

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)

 

[DrDu]

That's only true for the ionization of neutral atoms, not for the ionization of anions.

 

[harman90]

So it means , In case anions, IE is negative ?

I can't find any link favouring that statement ? Can you give me any source ?

 

[DrDu]

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.

 

[harman90]

2nd Ionization enthalpy... is actually removing electron from the ION.

infact all the successive Ionization energies are for Removing electrons from Ions.

 

[DrDu]

That's why they are explicitly called second IEs.

 

[Useful nucleus]

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^-

 

[harman90]

Thank you very much ... It makes sense now.