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，將使一個電子脫離一個氣態的離子或分子所需耗費，或是釋出的能量。

X⁻_(g) → X_(g) + e⁻ ΔH=E_ea

在固態物理學之中，對於一表面的電子親合能定義不同。

其他定義

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 價離子時放出的能量。此定義下的電子親合能和定義一相同。不過此定義下，放出能量時電子親和能為正，吸收能量時電子親和能為負，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 價離子時的能量變化。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。

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）
鋰	59.62	Hotop & Lineberger (1985). Dellwo et al. (1992). Haeffler et al. (1996a).
鈹	-48±20（估計）
硼	26.99	Scheer, Bilodeau & Haugen (1998).
碳	121.78	Scheer et al. (1998a).
氮	-6.8
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）
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
砹	270.1

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。

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

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