Calculate electron affinity from system and anion energies, or find Mulliken electronegativity from ionization energy and electron affinity.

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Positive electron affinity means energy is released. Use gas-phase energies on the same reference. Mulliken electronegativity here has energy units.

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Electron Affinity Formula

The following two example problems outline the steps and information needed to calculate the Electron Affinity.

EA = Ee - Ea

Variables:

  • EA is the electron affinity (eV per particle, or a consistent molar energy unit); positive means energy is released
  • Ee is the energy of the neutral atom plus a free electron on the chosen reference
  • Ea is the energy of the anion 

To calculate electron affinity, subtract the anion energy from the neutral-atom plus free-electron energy, using the same reference and units. For Mulliken electronegativity, use ฯ‡M = (IE + EA)/2; this unscaled average has energy units, not the dimensionless Pauling scale.

How to Calculate Electron Affinity?

The following steps outline how to calculate the Electron Affinity.

  1. First, determine the energy of the neutral atom plus a free electron on a consistent reference.
  2. Next, determine the energy of the anion. 
  3. Next, gather the formula from above = EA = Ee - Ea.
  4. Finally, calculate the Electron Affinity.
  5. After inserting the variables and calculating the result, check your answer with the calculator above.

Example Problem : 

Use the following variables as an example problem to test your knowledge.

energy of the neutral atom plus a free electron = 5 eV

energy of the anion = 3 eV

EA = Ee - Ea = 5 eV - 3 eV = 2 eV (energy released)