IONIC-RADII - EFFECT OF SHELL RADIUS, CATION CHARGE AND LONE ELECTRON-PAIR

Radii of ions, r(i), were compared with radii of their outermost orbit als, <r(nl)>. It has been found that for s and p block elements in the oxidation state equal to the group number, r(i) is a Linear function of <r(nl)> and, for a constant value of <r(nl)>, decreases with increa sing formal charge of the cation. For p block elements in the oxidatio n state two less than the group number, the difference r(i) - <r(nl)> as well as the difference in orbital energies, epsilon(np) - epsilon(n s), exhibit sawtooth behavior, i.e., secondary periodicity, similar to that in stability of oxidation states. The sawtooth behavior in the r adii suggests that the lone pair acquires some s(2) character between the third and fourth period, and becomes mainly an s(2) pair in the si xth period ions, particularly in Tl(+1). The radii of Lr(+1), 104(+4) and 105(+5) have been estimated from linear relationships between r(i) and <r(nl)>, and those of Al(+1), Ga(+1), In(+1) and Si(+2) from the sawtooth pattern.