[fluorineacid]

While I look at the table of element property, I learned that even the highest ionization energy(Cl) is lower than the lowest electron affinity(Cs).

Is there any reason to be like this, or just incidental?

I expect this result comes from the electron shell number, but if you know something about this please reply so I can understand this.

Thanks

[Alpha-Omega]

Please help me to understand what you are asking....


There are 7 ionization energies for chlorine (Cl)...the highest being 11,000 kJ/mol.

The electron affinity for Cesium (Cs) is 45.51 kJ/mol

And you are trying to compare/correlate what?  I am not following what is confusing you?  You have two different values for two different types of energy for two different elements and you are asking/comparing what exactly? ....and why those two??

What do you suspect comes from their electron configurations?  I am unclear as to what you are comparing and why?

Cs =  [Xe]6S¹ I am using shorthand notation here....(2 8 18 18 1)
Cl = 1s²  2s² 2p⁶ 3s² 3p⁵    ( 2, 8, 7)

[fluorineacid]

Oh, sorry I mean first ionization energy of cesium and first electron affinity of chlorine, not reverse.

In Misseler - Tarr it says that

The electron affinities are all much smaller than the corr. ionization E's because electron removal from a negative ion is easier than removal from a nut ion.

but it doesn't makes this problem clear for me.

[Alpha-Omega]

If you ionize Cs...it becomes Cs+ and the e;ectron configuration becpmes [Xe}...iCs is now isolectronic with xenon which has a nobel gas configuration-closed full shell...very stable...has 8 electrons in the outer shell.

Cs [Xe] 6s¹

Cs⁺[Xe]

For Cl....Cl has a high e;lectron affinity (desire for an electron) because it only needs to gain one electron to be isolectronic with argon.

Cl [Ne] 3s²3p⁵

Cl^- [Ar]

The Cl- ion has a closed shell electron configuration that is isoelectronic with argon.  Argon is a nobel gas and highly stable ...with a full shell of 8 electrons.

[Yggdrasil]

Perhaps the issue will be more clear if we explicitly write the meanings of ionization energy and electron affinity.  The first ionization energy of an element X is defined as the change in enthalpy of the following reaction:

X --> X⁺ + e^-

Electron affinity is defined as the change in enthalpy of this reaction:

X^- --> X + e^-

So, the ionization energy is the energy needed to remove an electron from a neutral species while electron affinity is the energy needed to remove an electron from a negatively charged species.  Because of electrostatic repulsion between electrons, it will be easier to remove an electron from a negatively charged species than a neutrally charged species.