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Electron Affinity for Dummies

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Manuel Robles

on 7 November 2013

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Transcript of Electron Affinity for Dummies

The First Electron Affinity
The Opposites
The greater the distance, the less the attraction and so the less energy is released as electron affinity.
The farther to the left and down an element is, the weaker its electron affinity.
A weaker attraction means low energy.
The Specifics
Electron Affinity on the Periodic Table
The Quickie
If the value assigned to Eea is negative, the negative sign implies a reversal of direction, and energy is required to attach an electron.
The usual expression for calculating Eea when an electron is attached is
Eea = (Einitial − Efinal)attach = −ΔE(attach)
Electron Affinity for Dummies
Ionization is the formation of a Cation.
Electron affinity is the formation of Anion equivalents.
The First Electron Affinity is the energy released when one mole of a gaseous atom acquires an electron, and therefore has negative values.
X(g) + e- X-(g) is the energy released per mole of X when this change happens. All first electron Affinities have negative values.
The First Electron Affinity
Electron Affinity as seen on The Periodic Table
Affinity Decreases
As you move up the Periodic Table, Electron Affinity becomes stronger and has more energy.
The same is true for when you travel to the right, the farther you go the stronger the affinity.
Electron Attraction depends on attraction between the electron and nucleus. A stronger attraction means more energy.
Robert S. Mulliken
Developed an electronegativity scale for atoms, equal to the average of the electron affinity and ionization potential.
Robert S. Mulliken, Journal of Chemical Physics, 1934
Mulliken's idea's opposite.
A molecule or atom that has a more positive value of electron affinity than another is often called an electron acceptor and the less positive an electron donor.
. Electron capture for almost all non-noble gas atoms involves the release of energy and thus are exothermic.
Slightly violent exothermic reaction
X− → X + e−
Electron affinity can be defined as the amount of energy required to detach an electron from a singly charged negative ion, i.e. the energy change for the process.
Atoms whose anions are more stable than neutral atoms have a greater Eea.
Example
Electron Affinities of the Elements
Eea generally increases across a period (row) in the periodic table. This is caused by the filling of the valence shell of the atom.
The additional electron will be entering an orbital farther away from the nucleus. Since this electron is farther from the nucleus it is less attracted to the nucleus and would release less energy when added.
Cl and Na satisfy their need for stability.
The Second Electron Affinity
You are only ever likely to meet this with respect to the group 6 elements oxygen and sulfur which both form 2- ions.
The second electron affinity is the energy required to add an electron to each ion in 1 mole of gaseous 1- ions to produce 1 mole of gaseous 2- ions.
anion
electron
yield
2nd Electron Affinity
You are forcing an electron into an already negative ion. It's not going to go in willingly!
2nd E.A.
The positive sign shows that you have to put in energy to perform this change. The second electron affinity of oxygen is particularly high because the electron is being forced into a small, very electron-dense space.
Citations, Citations for All!
(This statement is endorsed by Police officers everywhere.)
http://www.chemguide.co.uk/atoms/properties/eas.html, Awesome info
http://www.wikipedia.com, Awesome info
http://prezi.com/, Awesome presentation site!
Awesome sitckers, emoticons, and assorted fun things I used to make this just a little better.
Robert S. Mulliken, Journal of Chemical Physics, 1934, 2, 782.
Tro, Nivaldo J. (2008). Chemistry: A Molecular Approach (2nd Edn.). New Jersey: Pearson Prentice Hall
You get extra credit, and you get extra credit, EVERYBODY gets extra credit today! (This message is approved by Opra Winphrey.)
A big thanks to the following people...
Frankie Cisneros, A-Grade information, he knows his stuff!
Mariana Velazquez, A-Grade information, Chemistry Beast!
And um... oh right!
Me! Your friendly, neighborhood, presentation maker extraoirdinaire, Manuel Robles.
The electron enters the farthest shell from the nucleus.
Eea increases as you go along the periods, or rows.
The Process
An electron added with energy goes to the farthest valence shell.
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