电子亲合能

在一般化学与原子物理学中，电子亲合能（或电子亲和势、电子亲和力，electron affinity，Eea）的定义是，将单个电子结合到电中性的气态原子或分子上所释放的能量：
:X(g) + e− →  X−(g) + Eea
注意在此定义下，大多数元素原子的电子亲和能为正数，即结合电子的过程是放热的。这里定义的电子亲和能的正负号选取和一般热力学的定义相反。
在固态物理学之中，对于一表面的电子亲合能定义不同。

**元素的电子亲合能**
并非所有的元素的电子亲合能均为正，电子亲合能为正表示其 -1 价的离子需吸收能量才能变为电中性的原子（早期的教科书写有些元素，例如稀有气体，其电子亲合能为负，此说法并未被现代的化学家接受）。若其阴离子较不稳定，容易变成原子，则其电子亲合能较低。元素中氯的电子亲合能最高，汞和稀有气体等元素的电子亲合能都接近零。一般来说，非金属的电子亲合能都比金属高。
总的来说，同一周期从左至右，价壳层电子递增，使得原子稳定性上升，原子半径递减，对电子的吸引能力渐强，因而电子亲合能递增；同族元素从上到下，因原子半径的增大，而且总电子数增加，原子稳定性下降，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**
下列数据以kJ/mol为单位。带星号的元素在量子力学基态被认为有接近零的电子亲合能。

**列表及参考资料**

**分子的电子亲合能**
电子亲合能 Eea 的定义也可以延伸到分子。如苯和萘的电子亲合能为负值，而蒽
、菲、芘的电子亲合能为正值。电脑模拟实验证实六氰基苯 C6(CN)6 的电子亲合能较富勒烯要高。

**列表及参考资料**

**参见**
Koopmans' theorem
*One-electron reduction
*游离能
*电负性
*价电子

**注释**

**参考资料**
以下许多参考资料的文章名称会连结至参考资料的本文，不过需要订阅或付费才能阅读。(摘要)会连结到参考资料的摘要，不需付费即可阅读。
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**外部链接**
 Electron affinity date=20070609215624 , IUPAC 金色书的定义- Article about Electron Affinity