## Electron Affinity

AnnaTong1E
Posts: 20
Joined: Fri Jul 15, 2016 3:00 am

### Electron Affinity

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
Posts: 16
Joined: Wed Sep 21, 2016 2:56 pm

### Re: Electron Affinity

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
Posts: 22
Joined: Fri Jul 22, 2016 3:00 am

### Re: Electron Affinity

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
Posts: 24
Joined: Wed Sep 21, 2016 2:56 pm

### Re: Electron Affinity

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
Posts: 20
Joined: Wed Sep 21, 2016 2:59 pm

### Re: Electron Affinity

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
Posts: 24
Joined: Wed Sep 21, 2016 2:56 pm

### Re: Electron Affinity

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
Posts: 25
Joined: Wed Sep 21, 2016 2:59 pm

### Re: Electron Affinity

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?