Using 129I as Mössbauer nucleus, the properties of ICl, IBr, and I2Cl8, as well as I2Cl 4Br2, were investigated. From the well-resolved spectra of the quadrupole splitting, the e*qQ, the i\ parameter, and the isomer shift with respect to the standard 66Zn129Te source are derived. These data are used to deduce the 5p electron population of I. On the basis of the sensitivity of the isomer shift to the s character of the bond, it is shown that no sp hybridization occurs. The linear dependence of the isomer shift on the p holes is found to extend to hp values higher than 1. A relationship is derived to include hs, as well as hp when iodine is in a high valence state.