This page deals with the electron affinity as a property of isolated atoms or molecules (i.e. in the gas phase). Solid state electron affinities are not listed here.

Elements

Electron affinity can be defined in two equivalent ways. First, as the energy that is released by adding an electron to an isolated gaseous atom. The second (reverse) definition is that electron affinity is the energy required to remove an electron from a singly charged gaseous negative ion. The latter can be regarded as the ionization energy of the −1 ion or the zeroth ionization energy. Either convention can be used.

Negative electron affinities can be used in those cases where electron capture requires energy, i.e. when capture can occur only if the impinging electron has a kinetic energy large enough to excite a resonance of the atom-plus-electron system. Conversely electron removal from the anion formed in this way releases energy, which is carried out by the freed electron as kinetic energy. Negative ions formed in these cases are always unstable. They may have lifetimes of the order of microseconds to milliseconds, and invariably autodetach after some time.

† A quantum offset of the velocity imaging-based measurements was revealed in 2025, which could make a revision of all electron affinities marked with a dagger † necessary. The value of the downward correction to be applied is determined by the intensity of the electric field that was used in the experiment, which was not published with the original measurements, but can be estimated to be of the order of −20 μeV. However, subsequent studies have called both the magnitude and the very existence of such a quantum offset into question. A 2026 evaluation that combined simulations and high-precision experiments found no evidence for a quantum offset as large as 0.2 cm⁻¹ in properly analyzed slow‑electron velocity‑map imaging (SEVI) data. The original claim of a quantum offset in SEVI measurements rests on incorrect assumptions made in the LPM method. Moreover, the electron affinity of selenium determined by the LPM method deviates by approximately 0.5 cm⁻¹ from the values obtained with SEVI and with earlier laser photodetachment threshold (LPT) measurements. This discrepancy suggests that the LPM method alone may not provide a sufficiently reliable benchmark for validating other experimental techniques.

ZElementNameElectron affinity (eV)Electron affinity (kJ/mol)References11HHydrogen0.754 195(19)72.769(2)12HDeuterium0.754 67(4)72.814(4)2HeHelium−0.5(2) −48(20) est.3LiLithium0.618 049(22)59.632 6(21)4BeBeryllium−0.5(2)−48(20) est.5BBoron0.279 723(25)26.989(3)612CCarbon1.262 122 6(11)121.776 3(1)613CCarbon1.262 113 6(12)121.775 5(2)7NNitrogen−0.07−6.8 816OOxygen1.461 112 97(9)140.975 970(9)817OOxygen1.461 108(4)140.975 5(3)818OOxygen1.461 105(3)140.975 2(3)9FFluorine3.401 189 8(24)328.164 9(3)10NeNeon−1.2(2) −116(19)est.11NaSodium0.547 926(25)52.867(3)12MgMagnesium−0.4(2)−40(19)est.13AlAluminium0.432 83(5)41.762(5)14SiSilicon1.389 521 2(8)134.068 4(1)15PPhosphorus0.746 609(11)72.037(1)1632SSulfur2.077 104 2(6)200.410 1(1)1634SSulfur2.077 104 5(12)200.410 1(2)17ClChlorine3.612 725(28)348.575(3)18ArArgon−1.0(2)−96(20)est.19KPotassium0.501 459(13)48.383(2)20CaCalcium0.024 55(10)2.37(1)21ScScandium0.179 380(23)†17.307 6(22)22TiTitanium0.075 54(5)†7.289(5)23VVanadium0.527 66(20)†50.911(20)24CrChromium0.675 928(27)†65.217 2(26)25MnManganese−0.5(2)−50(19)est.26FeIron0.153 236(35)†14.785(4)27CoCobalt0.662 255(47)†63.897 9(45)28NiNickel1.157 16(12)111.65(2)29CuCopper1.235 78(4)119.235(4)30ZnZinc−0.6(2)−58(20)est.31GaGallium0.301 166(15)†29.058 1(15)32GeGermanium1.232 676 4(13)118.935 2(2)3375AsArsenic0.804 486(3)77.621 1(3)34SeSelenium2.020 667(5)194.964 8(5)35BrBromine3.363 588(3)324.536 9(3)36KrKrypton−1.0(2)−96(20)est.37RbRubidium0.485 916(21)46.884(3)38SrStrontium0.052 06(6)5.023(6)39YYttrium0.311 29(22)†30.035(21)40ZrZirconium0.433 28(9)†41.806(9)41NbNiobium0.917 40(7)†88.516(7)42MoMolybdenum0.747 23(8)†72.097(8)43TcTechnetium0.55(20)53(20)est.44RuRuthenium1.046 27(2)†100.950(3)45RhRhodium1.142 89(20)110.27(2)46PdPalladium0.562 14(12)54.24(2)47AgSilver1.304 47(3)125.862(3)48CdCadmium−0.7(2)−68(20)est.49InIndium0.38392(6)37.043(6)50SnTin1.112 070(2)107.298 4(3)51SbAntimony1.047 401(19)101.059(2)52TeTellurium1.970 875(7)190.161(1)53127IIodine3.059 046 5(37)295.153 1(4)53128IIodine3.059 052(38)295.154(4)54XeXenon−0.8(2)−77(20)est.55CsCaesium0.4715983(38)45.5023(4)56BaBarium0.144 62(6)13.954(6)57LaLanthanum0.557 546(20)†53.795(2)58CeCerium0.600 160(27)†57.906 7(26)59PrPraseodymium0.109 23(46)†10.539(45) 60NdNeodymium0.097 49(33)†9.406(32)61PmPromethium0.129 12.45 62SmSamarium0.162 15.63 63EuEuropium0.116(13)11.2(13)64GdGadolinium0.212(30)†20.5(29)65TbTerbium0.131 31(80)†12.670(77) 66DyDysprosium0.015(3)1.45(30)67HoHolmium0.338 32.61 68ErErbium0.31230.10 69TmThulium1.029(22)99(3)70YbYtterbium−0.02−1.93 est.71LuLutetium0.238 8(7)†23.04(7)72HfHafnium0.178 0(7)†17.18(7)73TaTantalum0.328 859(23)†31.730 1(22)74WTungsten0.816 500(82)†78.780 3(80)75ReRhenium0.060 396(64)†5.827 3(62)76OsOsmium1.077 661(24)†103.978 5(24)77IrIridium1.564 057(12)†150.908 6(12)78PtPlatinum2.125 10(5)205.041(5)79AuGold2.308 610(25)222.747(3)80HgMercury−0.5(2)−48(20)est.81TlThallium0.320 053(19)30.880 4(19)82PbLead0.356 721(2)34.418 3(3)83BiBismuth0.942 362(13)90.924(2)84PoPolonium1.40(7)136(7)calc.85AtAstatine2.415 78(7)233.087(8)86RnRadon−0.7(2)−68(20)est.87FrFrancium0.48646.89est.88RaRadium0.109.648 5est.89AcActinium0.35 33.77est.90ThThorium0.607 69(6)†58.633(6)91PaProtactinium0.55 53.03est.92UUranium0.314 97(9)†30.390(9)93NpNeptunium0.48 45.85 est.94PuPlutonium−0.50 −48.33 est.95AmAmericium0.10 9.93 est.96CmCurium0.28 27.17 est.97BkBerkelium−1.72 −165.24 est.98CfCalifornium−1.01 −97.31 est.99EsEinsteinium−0.30 −28.60 est.100FmFermium0.35 33.96 est.101MdMendelevium0.98 93.91 est.102NoNobelium−2.33 −223.22 est.103LrLawrencium−0.31 −30.04 est.111RgRoentgenium1.565 151.0calc.113NhNihonium0.69 66.6calc.115McMoscovium0.366 35.3calc.116LvLivermorium0.776 74.9calc.117TsTennessine1.719 165.9calc.118OgOganesson0.080(6) 7.72(58)calc.119UueUnunennium0.662 63.87 calc.120UbnUnbinilium0.0212.03calc.121UbuUnbiunium0.57 55 calc.

Molecules

The electron affinities Eea of some molecules are given in the table below, from the lightest to the heaviest. Many more have been listed by . The electron affinities of the radicals OH and SH are the most precisely known of all molecular electron affinities.

MoleculeNameEea (eV)Eea (kJ/mol)ReferencesDiatomics16OHHydroxyl1.827 6488(11)176.3413(2)16OD 1.825 53(4)176.137(5)C2Dicarbon3.269(6)315.4(6)BOBoron oxide2.508(8)242.0(8)NONitric oxide0.026(5)2.5(5)O2Dioxygen0.450(2)43.42(20)32SHSulfhydryl2.314 7283(17)223.3373(2)F2Difluorine3.08(10)297(10)Cl2Dichlorine2.35(8)227(8)Br2Dibromine2.53(8)244(8)I2Diiodine2.524(5)243.5(5)IBrIodine monobromide2.512(3)242.4(4)LiClLithium chloride0.593(10)57.2(10)FeOIron(II) oxide1.4950(5)144.25(6)CNCyano radical3.862(4) 372.6263Calculated on basis of the values for sulhydryl and the eV value of the cyano radical as the kJ/Mol value was missing from the list on march 18, 2025. TriatomicsNO2Nitrogen dioxide2.273(5)219.3(5)O3Ozone2.1028(25)202.89(25)SO2Sulfur dioxide1.107(8)106.8(8)Larger polyatomicsCH2CHO1.8248(+2-6)176.07(+3-7) after C6H6Benzene−0.70(14)−68(14)C6H4O2p-Benzoquinone1.860(5)179.5(6)BF3Boron trifluoride2.65(10)256(10)HNO3Nitric acid0.57(15)55(14)CH3NO2Nitromethane0.172(6)16.6(6)POCl3Phosphoryl chloride1.41(20)136(20)SF6Sulfur hexafluoride1.03(5)99.4(49)C2(CN)4Tetracyanoethylene3.17(20)306(20)WF6Tungsten hexafluoride3.5(1)338(10)UF6Uranium hexafluoride5.06(20)488(20)NIST chemistry webbook after C60Buckminsterfullerene2.6835(6)258.92(6)

Second and third electron affinity

ZElementNameElectron affinity (eV)Electron affinity (kJ/mol)References7N−Nitrogen−6.98−673Rayner-Canham Appendix 5: Data summarised from, and see also, J. E. Huheey et al., Inorganic Chemistry, 4th ed. (New York: HarperCollins, 1993) 7N2−Nitrogen−11.09−10708O−Oxygen−7.71−74415P−Phosphorus−4.85−46815P2−Phosphorus−9.18−88616S−Sulfur−4.73−45633As−Arsenic−4.51−43533As2−Arsenic−8.31−80234Se−Selenium−4.25−410

Bibliography . . Updated values can be found in the NIST chemistry webbook for around three dozen elements and close to 400 compounds.

Specific molecules

According to NIST as concerns Boron trifluoride, the Magnetron method, lacking mass analysis, is not considered reliable.

References

See also