电子亲合能

除以上定義（定義一）之外，電子親合能還有兩種定義方式：

定義二和定義一等價，是將一物質的原子或分子獲得一個電子，變成 -1 价离子時放出的能量。此定義下的電子親合能和定義一相同。不過此定義下，放出能量時电子亲和能為正，吸收能量時电子亲和能為負，正負號的使用和一般熱力學的定義恰好相反。

定義三，是將一物質的原子或分子獲得一個電子，變成 -1 价离子時的能量變化。^[2]放熱時數值為負，吸熱時數值為正。定義三的正負號使用和一般熱力學的定義相同。但其電子親合能恰為定義一的負值。(此定義為舊版IUPAC定義)

本文採用定義一的電子親合能。

並非所有的元素的電子親合能均為正，電子親合能為正表示其 -1 價的離子需吸收能量才能變為電中性的原子（早期的教科書寫有些元素，例如稀有氣體，其電子親合能為負，此說法並未被現代的化學家接受）。若其陰離子較不穩定，容易變成原子，則其電子親合能較低。元素中氯的電子親合能最高，汞和稀有氣體等元素的電子親合能都接近零。一般來說，非金屬的電子親合能都比金屬高。

总的来说，同一周期从左至右，價殼層電子递增，使得原子穩定性上昇，原子半径递减，对电子的吸引能力渐强，因而電子親合能递增；同族元素从上到下，因原子半径的增大，而且總電子數增加，原子穩定性下降，元素电负性值递减。实际上，随核电荷数递增或同族元素从上到下，电子亲和能的变化并不单调。

带有电子亲合能数据的元素周期表编辑

下列数据以kJ/mol为单位。带星号的元素在量子力学基態被认为有接近零的电子亲合能。

列表及参考资料编辑

電子親合能 E_ea 的定義也可以延伸到分子。如苯和萘的電子親合能為負值，而蒽、菲、芘的電子親合能為正值。電腦模擬實驗證實六氰基苯 C₆(CN)₆ 的電子親合能較富勒烯要高。^[5]

列表及参考资料编辑

• Koopmans' theorem
• One-electron reduction
• 游離能
• 电负性
• 价电子

1. ^ 國際純化學和應用化學聯合會，化學術語概略，第二版。（金皮書）(1997)。在線校正版: (2006–) "Electron affinity"。doi:10.1351/goldbook.E01977
2. ^ http://www.chemguide.co.uk/atoms/properties/eas.html （页面存档备份，存于互联网档案馆） 其定義的電子親合能均為負值
3. ^ ^{3.0 3.1 3.2 3.3} Bratsch, S.G.; Lagowski, J.J. Predicted stabilities of monatomic anions in water and liquid ammonia at 298.15 K.. Polyhedron. 1986, 5 (11): 1763–1770. doi:10.1016/S0277-5387(00)84854-8. 
4. ^ ^{4.0 4.1} 存档副本. [2019-12-28]. （原始内容存档于2020-02-03）. 
5. ^ Remarkable electron accepting properties of the simplest benzenoid cyanocarbons: hexacyanobenzene, octacyanonaphthalene and decacyanoanthracene Xiuhui Zhang, Qianshu Li, Justin B. Ingels, Andrew C. Simmonett, Steven E. Wheeler, Yaoming Xie, R. Bruce King, Henry F. Schaefer III and F. Albert Cotton Chemical Communications, 2006, 758 - 760 Abstract

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• Electron affinity （页面存档备份，存于互联网档案馆）, IUPAC 金色書的定義
• Article about Electron Affinity