To me, conceptually, Al seems to fit in with In/Ga because their halides are Lewis acids, while scandium trihalides are weakly acidic and Y/La halides
are essentially nonacidic. B/Al/Ga/In hydrides can be made by hydrogenation of the chlorides and form tetrahydridometallates, while ScH3 is incredibly
unstable and lithium scandium hydride does not seem to be described. Yttrium meanwhile reacts with hydrogen gas to form hydrides which are apparently
thermodynamically stable, a behavior not seen in any poor metal (and all of their hydrides are >0 H_f). |