電子親合能

在一般化學與原子物理學中，電子親合能（或電子親和勢、電子親和力，electron affinity，E_ea）的定義是，將單個電子結合到電中性的氣態原子或分子上所釋放的能量^[1]：

X(g) + e⁻ → X⁻(g) + E_ea

注意在此定義下，大多數元素原子的電子親和能為正數，即結合電子的過程是放熱的。這裏定義的電子親和能的正負號選取和一般熱力學的定義相反。

在固態物理學之中，對於一表面的電子親合能定義不同。

元素的電子親合能

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。

總的來說，同一週期從左至右，價殼層電子遞增，使得原子穩定性上昇，原子半徑遞減，對電子的吸引能力漸強，因而電子親合能遞增；同族元素從上到下，因原子半徑的增大，而且總電子數增加，原子穩定性下降，元素電負性值遞減。 實際上，隨核電荷數遞增或同族元素從上到下，電子親和能的變化並不單調。

帶有電子親合能數據的元素週期表

下列數據以kJ/mol為單位。帶星號的元素在量子力學基態被認為有接近零的電子親合能。

週期

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

電子層

Ｏ族電子數

族

I A

0

1

73 H 氫

* He 氦

K

2

II A

III A

IV A

V A

VI A

VII A

2

60 Li 鋰

* Be 鈹

27 B 硼

122 C 碳

−7 N 氮

141 O 氧

328 F 氟

* Ne 氖

L K

8 2

3

53 Na 鈉

* Mg 鎂

42 Al 鋁

134 Si 硅

72 P 磷

200 S 硫

349 Cl 氯

* Ar 氬

M L K

8 8 2

III B

IV B

V B

VI B

VII B

VIII

I B

II B

4

48 K 鉀

2 Ca 鈣

18 Sc 鈧

8 Ti 鈦

51 V 釩

65 Cr 鉻

0 Mn 錳

15 Fe 鐵

64 Co 鈷

112 Ni 鎳

119 Cu 銅

* Zn 鋅

41 Ga 鎵

119 Ge 鍺

79 As 砷

195 Se 硒

325 Br 溴

* Kr 氪

N M L K

8 18 8 2

5

47 Rb 銣

5 Sr 鍶

30 Y 釔

41 Zr 鋯

86 Nb 鈮

72 Mo 鉬

53 Tc 鍀

101 Ru 釕

110 Rh 銠

54 Pd 鈀

126 Ag 銀

* Cd 鎘

39 In 銦

107 Sn 錫

101 Sb 銻

190 Te 碲

295 I 碘

* Xe 氙

O N M L K

8 18 18 8 2

6

46 Cs 銫

14 Ba 鋇

鑭系

* Hf 鉿

31 Ta 鉭

79 W 鎢

15 Re 錸

104 Os 鋨

150 Ir 銥

205 Pt 鉑

223 Au 金

* Hg 汞

36 Tl 鉈

35 Pb 鉛

91 Bi 鉍

190 Po 釙

270 At 砹

* Rn 氡

P O N M L K

8 18 32 18 8 2

7

Fr 鈁

Ra 鐳

錒系

Rf 鑪

Db 𨧀

Sg 𨭎

Bh 𨨏

Hs 𨭆

Mt 䥑

Ds 鐽

Rg 錀

Cn 鎶

Nh 鉨

Fl 鈇

Mc 鏌

Lv 鉝

Ts 鿬

Og 鿫

鑭系元素

45 La 鑭

92 Ce 鈰

Pr 鐠

Nd 釹

Pm 鉕

Sm 釤

Eu 銪

Gd 釓

Tb 鋱

Dy 鏑

Ho 鈥

Er 鉺

99 Tm 銩

Yb 鐿

33 Lu 鑥

錒系元素

Ac 錒

Th 釷

Pa 鏷

U 鈾

Np 錼

Pu 鈽

Am 鋂

Cm 鋦

Bk 鉳

Cf 鐦

Es 鎄

Fm 鐨

Md 鍆

No 鍩

Lr 鐒

鹼金屬	鹼土金屬	鑭系元素	錒系元素	過渡金屬
主族金屬	類金屬	非金屬	鹵素	貴氣體

列表及參考資料

元素	電子親合能 (kJ/mol)	參考資料
氫	72.77	Pekeris (1962). Lykke, Murray & Lineberger (1991).
氦	-48±20（估計）	[2]
鋰	59.62	Hotop & Lineberger (1985). Dellwo et al. (1992). Haeffler et al. (1996a).
鈹	-48±20（估計）	[2]
硼	26.99	Scheer, Bilodeau & Haugen (1998).
碳	121.78	Scheer et al. (1998a).
氮	-6.8	[2]
氧	141.004	Hotop & Lineberger (1985). Blondel (1995). Valli, Blondel & Delsart (1999).
氟	328.165	Blondel et al. (1989). Blondel, Delsart & Goldfarb (2001).
氖	-116±19（估計）	[2]
鈉	52.87	Hotop & Lineberger (1985)
鋁	41.86	Scheer et al. (1998b)
矽	134.07	Scheer et al. (1998a). Blondel, Delsart & Goldfarb (2001).
磷	72.03	Hotop & Lineberger (1985).
硫	200.410	Blondel (1995).
氯	349	Moore (1970).
鉀	48.38	Slater et al. (1978). Andersson et al. (2000).
鈣	2.37	Petrunin et al. (1996).
鈧	18(2)	Feigerle, Herman & Lineberger (1981).
鈦	8.4(7)	Ilin, Sakharov & Serenkov (1987).
釩	51	Hotop & Lineberger (1985).
鉻	65.2	Bilodeau, Scheer & Haugen (1998).
鐵	14.6(3)	Leopold & Lineberger (1986).
鈷	64.0	Scheer et al. (1998c).
鎳	111.6	Scheer et al. (1998c).
銅	119.24	Bilodeau, Scheer & Haugen (1998).
鎵	41(3)	Williams et al. (1998a).
鍺	118.94	Scheer et al. (1998a).
砷	78.5(7)	Lippa et al. (1998).
硒	194.97	Hotop & Lineberger (1985). Mansour et al. (1988).
溴	342.54	Blondel et al. (1989).
銣	46.89	Frey, Breyer & Hotop (1978).
鍶	5.02	Andersen et al. (1997).
釔	30	Feigerle, Herman & Lineberger (1981).
鋯	41	Hotop & Lineberger (1985).
鈮	86(2)	Hotop & Lineberger (1985).
鉬	72.3	Bilodeau, Scheer & Haugen (1998).
釕	101.0	Norquist et al. (1999).
銠	110.3	Scheer et al. (1998c).
鈀	54.24	Scheer et al. (1998c).
銀	125.86	Biladeau, Scheer & Haugen (1998).
銦	39	Williams et al. (1998b).
錫	107.30	Scheer et al. (1998a).
銻	101.06	Scheer, Haugen & Beck (1997).
碲	190.16	Hotop & Lineberger (1985). Haeffler et al. (1996b).
碘	295	Moore (1970).
銫	45.51	Slater et al. (1978). Scheer et al. (1998d).
鋇	13.95	Petrunin et al. (1995).
鑭	45(2)	Covington et al. (1998).
鈰	92(2)	Davis & Thompson (2002a).
銩	99(2)	Davis & Thompson (2002b).
鎦	33	Davis & Thompson (2001).
鉿	0.00	Periodic Table of the Elements(2017)
鉭	31	Hotop & Lineberger (1985).
鎢	79	Hotop & Lineberger (1985). Bengali et al. (1992).
鋨	104.0	Biladeau & Haugen (2000).
銥	150.9	Biladeau et al. (1999).
鉑	205.04	Biladeau et al. (1999).
金	222.75	Hotop & Lineberger (1985).
鉈	36	Carpenter, Covington & Thompson (2000).
鉛	35	Hotop & Lineberger (1985).
鉍	90.92	Biladeau & Haugen (2001).
釙	183.3	[3]
砹	270.1	[3]

分子的電子親合能

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。^[4]

列表及參考資料

分子	電子親合能 (kJ/mol)	參考資料
雙原子分子
溴分子	244	Janousek & Brauman (1979)
氯氣	227	Janousek & Brauman (1979)
氟氣	297	Janousek & Brauman (1979)
碘分子	246	Janousek & Brauman (1979)
氧氣	43	CRC Handbook
溴化碘	251	Janousek & Brauman (1979)
氯化鋰	59	Janousek & Brauman (1979)
一氧化氮	2	Janousek & Brauman (1979)
三原子分子
二氧化氮	222	Janousek & Brauman (1979)
二氧化硫	105	Janousek & Brauman (1979)
多原子分子
苯	−110	Janousek & Brauman (1979)
1,4-苯二酮	129	CRC Handbook
三氟化硼	255	CRC Handbook
硝酸	59	Janousek & Brauman (1979)
硝基甲烷	38	Janousek & Brauman (1979)
三氯化磷	134	Janousek & Brauman (1979)
六氟化硫	138	CRC Handbook
四氰乙烯	278	CRC Handbook
六氟化鎢	264	CRC Handbook
六氟化鈾	280	CRC Handbook

參見

• Koopmans' theorem
• One-electron reduction
• 游離能
• 電負性
• 價電子

註釋

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. 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.
3. 存档副本. [2019-12-28]. （原始內容存檔於2020-02-03）.
4. 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

參考資料

以下許多參考資料的文章名稱會連結至參考資料的本文，不過需要訂閱或付費才能閱讀。(摘要)會連結到參考資料的摘要，不需付費即可閱讀。

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外部連結

• Electron affinity （頁面存檔備份，存於互聯網檔案館）, IUPAC 金色書的定義
• Article about Electron Affinity