Use our electron affinity calculator for quick and accurate calculations. Free online tool.
The Electron Affinity Calculator helps you determine the energy change when a neutral atom in the gas phase gains an additional electron to form a negative ion. Electron affinity (EA) is a fundamental periodic property that indicates how strongly an atom attracts an extra electron. A large negative value means the process is highly exothermic and the atom readily accepts electrons.
Electron affinity is expressed in kJ/mol or electronvolts (eV). Chlorine has one of the highest electron affinities at −349 kJ/mol (−3.62 eV), meaning it releases 349 kJ per mole when each Cl atom gains one electron: Cl(g) + e⁻ → Cl⁻(g), ΔH = −349 kJ/mol. Fluorine, despite being the most electronegative element, has a slightly lower EA of −328 kJ/mol due to electron-electron repulsion in its compact 2p orbital.
Enter the element symbol or atomic number to retrieve its first electron affinity. The calculator supports values in both kJ/mol and eV, and covers all main-group elements plus selected transition metals. Use cases include predicting oxidizing power, comparing halogen reactivity, and understanding electronegativity trends across the periodic table.
Atomic radius, ionization energy, electron affinity, electronegativity, and periodic trends
Explore CategoryElectron affinity is the energy released or absorbed when a neutral gaseous atom gains one electron to form a negative ion. Negative values indicate an exothermic (favorable) process.
Chlorine has the highest first electron affinity at −349 kJ/mol, slightly exceeding fluorine (−328 kJ/mol) due to less electron repulsion in its larger 3p orbital.
Yes. Noble gases and alkaline earth metals like beryllium have positive (endothermic) electron affinities because adding an electron is energetically unfavorable.
Electron affinity measures the energy change for adding one electron to an isolated atom, while electronegativity measures the tendency to attract bonding electrons within a molecule.
Electron affinity is commonly expressed in kilojoules per mole (kJ/mol) or electronvolts (eV), where 1 eV ≈ 96.485 kJ/mol.