Question

5. PF5, shown below, is a trigonal bipyramidal molecule that has been described as “hypervalent” because it exceeds its valence octet. It has been observed that the axial ligands in such molecules must be electronegative. One molecular orbital description for this behaviour invokes the concept of a “three-centre four-electron bond” connecting the axial ligands. Is this model concept consistent with the requirement for electronegative axial ligands? Explain. (Hint: a molecular orbital diagram might help).

900 120°

Answer 1

there would be 3(ssp^2) ordinary (these will be used to create the equatorial and critical(this will be used to create over) According to Bent's rules phosphorus to use the arbitrary to form the p-F Bond and the ordinary with mass S- character the equatiponasl sp^2 ordinary to form- pcl In pF_5 3 educational have weight S character sop its have low electronegative In 2 a seal have high 'p' character so electronegative eubsitued occupies the axial positon and lens occupies t he axial position and less electronegative substituenent is equatorially if mixing as pcl_x F_5 - x