The "Anomalous" Electron Affinity of Lead An Example of lsoelectronic Behavior Jose Antonio Chamizo' Universidad Nacional Autbnoma de Mexlco. 04510 MBxico D.F., Mexico The electron affmity EA of an atom A, sometimes c d e d the zeroth ionization potential (I),has been defined as the difference between the total energies of the ground state of A and its negative ion A- ( 2 )
Some Energy T e r m (eV) for Group IVA Elements
Element
SpiMrblt
X
3Pr3P0
C
0.005 0.03
EA = EA- EA-
Si
Ionization Potential
Elecbon Affinity
Do
11.26
1.27 1.39
6.1 3.2
8.15
Xz bond
Recently the EA of lead was calculated by the technique of laser photoelectron spectrometry (LPES) (3)and was found to he 0.365 0.008 eV, a value very different from those reported earlier in the literature (1.1eV (2)and 1.05 0.09 eV
*
*
Electron
n-5
Figure 1. Ionization potential and electron affinity of the elements 01 groups 111, IV, and VB.
0.37.V
0.3."
'SX
TI-
095.V
'P
P b'
Figure 2. Effect of spin-wbit coupling on Me electron affinity of TI. Pb, and Bi (not drawn to scale).
874
Journal of Chemical Education
(4)). With this new value the periodicity of the EA in the sixth row differs from that of the rest of the representative elements in the same way that the periodicity of the ionization potential IP differs (Fie. 1). The anomajbus behavior of the IP of bismuth was discussed bv Smith (5 I in ierms of s~in-orbitcou~linr.The ex~lanation i'hasicall'; the same f o r t h e EA of lead, since both species involved are isoelectronic (Fig. 2). That is, the configuration of the following species is the same: Ph, Bi+ (6p2)and Ph-, Bi (603). l'l;e large stabilization of the ground state " 0 (see tahle) oithe 6p2configurationand the negligible stnhilizationof the 'S.
