1. Periodicity
Electron affinity

2. X- (g) + e- → X 2- (g) Electron affinity X(g) + e- → X- (g)
Electron affinity: is the energy change when one mole of electrons is added to one mole of gaseous atoms to form one mole of gaseous ions.
X(g) + e- → X- (g)
X- (g) + e- → X 2- (g)

3. Electron affinity continued…
Values for electron affinity can be found in the chem data booklet on page 8.
Make sure you are looking at the correct value as there are other terms listed with each element.
Since noble gases do not form ions easily they have no values reported on this table.

4. Electron affinity trends

5. The trend is not perfect…

6. What is the trend?
As you move up a group on the table and to the right in a period, the electron affinity increases.
Increasing electron affinity: ↑ group / → period
As you move down a group on the periodic table and to the left in a period, electron affinity decreases.
Decreasing electron affinity: ↓ group / ← period