Electron Affinity

[AnnaTong1E]

Could someone please give me a solid, clear definition of electron affinity? I understand ionization energy and atomic radius and their trends in the periodic table, but I don't think I fully understand electron affinity.

Thanks! :)

[GregoryPolyakov_1H]

From the internet

"Electron affinity is defined as the change in energy (in kJ/mole) of a neutral atom (in the gaseous phase) when an electron is added to the atom to form a negative ion. In other words, the neutral atom's likelihood of gaining an electron"

[EmmaSaid3C]

To add to that, electron affinity is the energy required/released to add one electron to an atom.

"For example, when a neutral chlorine atom in the gaseous form picks up an electron to form a Cl- ion, it releases an energy of 349 kJ/mol. It is said to have an electron affinity of -349 kJ/mol and this large number indicates that it forms a stable negative ion."

[Marisa_Woo_2G]

Furthermore, a higher electron affinity would mean that the element would like to pick up electrons to become more stable. If the element's electron configuration is more stable, there would be a lower electron affinity.

You can see this in the equation for electron affinity: Electron affinity = Energy of a neutral atom (w/o added electrons)-Energy of anion(added negative charge)

[Da_Rhee_1O]

What does the course reader mean when next to the electron affinity equation it says X(g) + e- -> X-(g) "DEFINED AS" Eea = E(X)(g) - E(X-)(g)

Is this the same equation rephrased differently? Just wanted clarification, please.

[Marisa_Woo_2G]

More or less, the two equations refer to the same concept.

"X" refers to a generic element (Element X: Cl, O, N, etc.) so the first equation would essentially be:
Generic element in a gas-phase + added electrons --> Generic element in a gas phase with a negative charge

The other equation refers to:
Energy released when electrons are added to the generic element in a gas phase/Electron Affinity= Energy of a neutral atom of the generic element - Energy of the anion (Generic element with a negative charge).

The first equation demonstrates how the anion is created, while the second equation refers to the release of energy/electron affinity I think.

[Kendall_Chaffin_3C]

In the book it says electron affinities are higher towards the right of the periodic table. But, group 15 elements have lower ionization energies then group 14. Why is this?