Electron Affinity Trend

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Electron Affinity (EA)
Electron affinity is the amount of energy involved with adding an electron to an atom or ion.

Wize Tip
Don't confuse ionization energy (IE) with electron affinity (EA)!
Ionization energy is when we remove the outermost electron
Electron affinity is when we add an electron
Memory tip: Electron affinity has an "a" in it for adding an electron

When adding an electron, do we get a cation or an anion? anion
!

       E+e−→E−ΔE=Electron Affinity\textbf{E}+\textbf{e}^-\rightarrow \textbf{E}^-\quad\quad\Delta \textbf{E}=\textbf{Electron Affinity}E+e−→E−ΔE=Electron Affinity 

If EA is negative → energy is released/absorbed: released 
If this is the case, would the atom go to a higher/lower E state? lower 
This means the atom has become more/less more
 stable as a result of adding an electron 
Did this atom like or dislike having an electron added to it? like
If EA is positive → energy is released/absorbed: absorbed
 
If this is the case, would the atom go to a higher/lower E state? higher
This means the atom has become more/less stable less
 stable as a result of adding an electron
Did this atom like or dislike having an electron added to it? dislike

Watch Out!
Use a negative EA as a reference point, unless the question states otherwise. 

This means that unless specified otherwise, when asked which element would have the largest electron affinity, assume they mean largest NEGATIVE electron affinity.
This would mean that the element really liked getting an electron and lost energy, resulting in a more stable form. 

The Periodic Trend

In general, as Zeff increases, the incoming electron experiences a greater electrostatic attraction and stabilization leading to a greater (negative) electron affinity


What about noble gases?
Do you think a noble gas would have a positive or negative electron affinity? Positive
Are noble gases stable? Yes!
Would a noble gas want another electron added? No!
If you tried to add an electron to a noble gas would that require energy or release energy? Require energy

Watch Out!
This trend excludes noble gases. Noble gases have stable, completely filled shells. Adding electrons to noble gases will break the noble gas configuration.

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Example: Increasing Electron Affinity
Rank the following atoms in increasing absolute energy of their first electron affinity: Br, Ag, Ba, Mo, Sb

Ba < Mo < Ag < Sb < Br

Practice: Positive Electron Affinity
For most elements, the first electron affinity is negative; however, a few elements have a positive first electron affinity. Which atom has the most positive first electron affinity?

Practice: Highest Electron Affinity
Which of the following has the highest electron affinity?

Wize High School Grade 12 Chemistry Textbook > Atomic Models and Properties of Atoms

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Electron Affinity (EA)

What about noble gases?

Example: Increasing Electron Affinity

Practice: Positive Electron Affinity

Practice: Highest Electron Affinity