Electron Affinity Calculator

Calculator Inputs

Calculation Mode * From energy levels Direct electron affinity From threshold wavelength

Choose how you want to compute the value.

Neutral energy, E(neutral) *

Energy of the neutral state.

Anion energy, E(anion) *

Energy of the negative ion state.

Energy unit eV kJ/mol J (per particle)

All results are standardized internally.

Electron affinity value *

Use positive values for released energy.

Electron affinity unit eV kJ/mol J (per particle)

Converts into multiple outputs automatically.

Threshold wavelength, λ *

Photodetachment threshold estimate.

Wavelength unit nm Å µm m

Converted internally to nanometers.

Calculate Reset

Formula Used

How to Use This Calculator

1. Select a calculation mode that matches your data.
2. Enter values and choose the correct units.
3. Click Calculate to view results above the form.
4. Use the export buttons to download CSV or PDF.
5. Interpret the sign: positive indicates released energy.

Example Data Table

Values are illustrative for demonstration and testing.

Professional Article

1) What electron affinity represents

Electron affinity (EA) quantifies the energy change when a neutral atom or molecule gains an electron to form an anion. In many tables, EA is reported as positive when energy is released (exothermic attachment). Some sources reverse the sign; verify the convention.

2) Typical magnitude and trends

For many elements, EA spans roughly 0 to 4 eV. Halogens tend to be high because they are one electron short of a closed shell, while noble gases often have near-zero or negative EA due to closed-shell stability. Periodic trends can guide sanity checks when validating inputs.

3) Energy-level definition in practice

When you know computed or measured energies for the neutral state and the anion, the most direct relation is EA = E(neutral) − E(anion). The subtraction matters more than each absolute sign.

4) Threshold wavelength method

In photodetachment, a photon with energy near the threshold can remove the extra electron. This gives the estimate EA ≈ hc/λ. Using hc = 1239.841984 eV·nm, a threshold at 343 nm corresponds to about 3.61 eV, while 1644 nm corresponds to about 0.754 eV, matching the example rows.

5) Units and conversion constants

This calculator standardizes results in eV, kJ/mol, and joules per particle. The fixed constants are 1 eV = 1.602176634 × 10⁻¹⁹ J and 1 eV per particle = 96.485 kJ/mol. Converting through these values prevents round-trip drift when exporting.

In solid-state contexts, EA connects to work function and electron transport; comparing values helps estimate charge transfer tendencies in materials and interfaces under illumination and applied fields.

6) Interpreting negative results

A negative EA implies that the anion is not energetically favored relative to the neutral species and a free electron. Such cases can still appear as transient resonances, especially for molecules, but they are less likely to form stable bound anions under low-energy conditions.

7) Quality checks for experimental and computed inputs

For measured thresholds, verify wavelength calibration and ensure the threshold corresponds to the correct electronic state. For computed energies, confirm consistent methods and basis sets for both neutral and anion. Small methodological mismatches can shift EA by tenths of an eV, which is significant for spectroscopy comparisons.

8) Using exports for reporting

CSV suits spreadsheets, while PDF suits sharing. Include the calculation mode and original inputs so collaborators can reproduce the result. Consistent metadata matters in collaborative analysis.

FAQs

1) Is electron affinity the same as ionization energy?

No. Ionization energy removes an electron from a neutral species, while electron affinity adds an electron to form an anion. They describe different processes and often follow different periodic trends.

2) Why do some sources report negative electron affinity?

Sign conventions vary. Some tables define EA as the energy required to attach an electron, making exothermic attachment negative. This calculator reports positive when energy is released.

3) What does the threshold wavelength output mean?

It is the photon wavelength whose energy matches the computed affinity using hc/λ. It is most meaningful for photodetachment-style estimates and requires EA > 0 to produce a finite wavelength.

4) Which unit should I use for chemistry reports?

Chemistry reports commonly use kJ/mol, while spectroscopy and atomic physics often use eV. Use the unit your field expects, and keep the conversion constant consistent across a dataset.

5) Can I use molecular electron affinities here?

Yes, if you supply consistent neutral and anion energies or a threshold wavelength. For molecules, negative or near-zero values can occur and may indicate weakly bound or resonance behavior.

6) Why is my result extremely large or tiny?

Most EAs are within a few eV. If you see outliers, check units (J vs kJ/mol vs eV) and ensure both energies refer to the same reference level and computational method.

7) Do the exports include my inputs?

Yes. The exported files include a stored input summary along with the calculated outputs, helping you reproduce the calculation later or share the exact assumptions with collaborators.