What is electron affinity?
Answers:
The electron affinity is a measure of the energy change when an electron is added to a neutral atom to form a negative ion. For example, when a neutral chlorine atom in the gaseous form picks up an electron to form a Cl- ion, it releases an energy of 349 kJ/mol or 3.6 eV/atom. It is said to have an electron affinity of -349 kJ/mol and this large number indicates that it forms a stable negative ion. Small numbers indicate that a less stable negative ion is formed. Groups VIA and VIIA in the periodic table have the largest electron affinities.
* Alkali earth elements (Group IIA) and noble gases (Group VIIIA) do not form stable negative ions.
Electron Affinities in kJ/mole
Period IA IIIA IVA VA VIA VIIA
Period 1 H . . . . .
-73 . . . . .
Period 2 Li B C N O F
-60 -27 -122 0 -141 -328
Period 3 Na Al Si P S Cl
-53 -44 -134 -72 -200 -349
Period 4 K Ga Ge As Se Br
-48 -30 -120 -77 -195 -325
Period 5 Rb In Sn Sb Te I
-47 -30 -121 -101 -190 -295
Period 6 Cs Tl Pb Bi Po At
-45 -30 -110 -110 -180 -270
Electron Affinities in Electron Volts
1 kJ/mol = .010364 eV/atom
Period IA IIIA IVA VA VIA VIIA
Period 1 H . . . . .
-0.76 . . . . .
Period 2 Li B C N O F
-0.62 -0.28 -1.27 0 -1.43 -3.41
Period 3 Na Al Si P S Cl
-0.55 -0.46 -1.39 -0.75 -2.08 -3.62
Period 4 K Ga Ge As Se Br
-0.50 -0.31 -1.25 -0.80 -2.02 -3.37
Period 5 Rb In Sn Sb Te I
-0.49 -0.31 -1.26 -1.05 -1.97 -3.06
Period 6 Cs Tl Pb Bi Po At
-0.47 -0.31 -1.14 -1.14 -1.87 -2.80
Periodic Table Chemical bonds
The electron affinity is a measure of the energy change when an electron is added to a neutral atom to form a negative ion.
The electron affinity of an element is the energy released when an electron is added to an isolated atom in the gaseous state, i.e. it is the decrease in energy for the process:
X(g) + e- = X-(g)
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