Note 158 — Chapter IX · GENERAL PROPERTIES OF THE CERIUM AND YTTRIUM GROUPS

The position of yttrium in this series is not known with certainty; it is probably as positive as neodymium. It is usually stated (see Meyer and Hauser, pp. 32-33) that the terbia oxides are intermediate in basic strength between the ceria and yttria earths, though the arrangement into two series, consisting of the cerium and yttrium groups respectively, is generally adopted; the electropositive character of the elements in each series then weakens as the atomic weight rises, scandium being of course exceptional.