Yttrium subgroup

There are two allotropic (crystal forms) of terbium, both of which are dependent on its temperature. The alpha ((a) form exists at room temperatures and up to temperamres of 1,298°C, and the beta ( 3) form exists beyond these temperamres. Although terbium is a silvery metal that resembles aluminum and feels hke lead, it is much heavier than either of these two elements. It is placed in the yttrium subgroup (lanthanide series) of the rare-earths. It is also resistant to corrosion. 

Erbium is a soft, malleable metal with a silvery metallic luster that only tarnishes (oxidi2es) slightly in air. It is one of the rare-earths of the yttrium subgroup of the lanthanide series. 

Thus the energy of formation of complexes in the rare earth series should vary in the same manner as the molar volumes and basic properties of hydroxides should vary in the opposite manner. It is clear from Fig. 3.14 that the ionic radii, molar volumes and the basic properties of hydroxides show negative deviations. The central members of the cerium subgroup show maximum deviations. The deviations shown by the yttrium subgroup are smaller than the cerium subgroup. This situation is analogous to the behaviour of transition... 

The elements 57-62 are known as the cerium subgroup, and 63-71 as the yttrium subgroup. Yttrium, atomic number 39, although not a rare-earth element, is found associated with the rare earths and is separated only with difficulty. 

CAS 7440-64-4. Yb. A metallic element. A rare-earth metal of yttrium subgroup, atomic number 70, aw 173.04, valence of 2, 3 exists in a and (3 forms, the latter being semiconductive at pressures above 16,000 atm. There are seven natural isotopes. 

The phosphates of the yttrium subgroup have the tetragonal zircon structure, which is isomorphic with the corresponding orthovanadates, arsenates, and chromates (Schwarz, 1963f). The crystal structure of xenotime has been deter-... 

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