Electron affinity

In chemistry, electron affinity is the amount of energy absorbed when an electron is added to a neutral isolated gaseous atom to form a gaseous ion with a 1- charge. It has a negative value if energy is released.

Most elements have a negative electron affinity. This means they do not require energy to gain an electron; instead, they release energy. Atoms more attracted to extra electrons have a more negative electron affinity. Chlorine most strongly attracts extra electrons; radon most weakly attracts an extra electron.

Although electron affinities vary in an chaotic manner across the table, some patterns amerge. Generally, nonmetals have more negative electron affinities than metals. However, the noble gases are an exception: they have positive electron affinities.

Electron affinity is influenced by the octet rule[?]. Group 1 elements (hydrogen, lithium, sodium, potassium, rubidium, calcium, and francium) tend to gain an electron and form -1 anions. The noble gases have a full octet, and thus adding an extra electron requires large amounts of energy, but it is possible.

Group

1

2

3[?]

4[?]

5[?]

6

7[?]

8[?]

9[?]

10[?]

11

12[?]

13

14

15

16

17

18

Period

1

H -73

He 21

2

Li -60

Be 19

B -27

C -122

N 7

O -141

F -328

Ne 29

3

Na -53

Mg 19

Al -43

Si -134

P -72

S -200

Cl -239

Ar 35

4

K -48

Ca 10

Sc -18

Ti -8

V -51

Cr -64

Mn

Fe -16

Co -64

Ni -112

Cu -118

Zn 47

Ga -29

Ge -116

As -78

Se -195

Br -325

Kr 39

5

Rb -47

Sr

Y -30

Zr -41

Nb -86

Mo -72

Tc -53

Ru -101

Rh -110

Pd -54

Ag -126

Cd 32

In -29

Sn -116

Sb -103

Te -190

I -295

Xe 41

6

Cs -45

Ba

Lu

Hf

Ta -31

W -79

Re -14

Os -106

Ir -151

Pt -205

Au -223

Hg 61

Tl -20

Pb -35

Bi -91

Po -183

At -270

Rn 41

7

Fr -44

Ra

Lr

Rf

Db

Sg

Bh

Hs

Mt

Ds

Uuu

Uub

Uut

Uuq

Uup

Uuh

Uus

Uuo

Periodic table of electron affinities, in kJ/mol