This decision did not fall from the moon, something of the sort had happened once before in the Periodic Table. The lanthanides, a total of 14 elements of the sixth period were all placed together with lanthanum in a single box of Group III.

   The physicists had long since predicted that a similar phenomenon would recur in the next period. They stated that a family of elements resembling the lanthanides should exist in the seventh period. The name of this family would be actinides, because it would begin right after actinium which is situated just below lanthanum in the table.

   Hence, all the transuranium elements are members of this family. And not only they, but also uranium and its nearest left-hand neighbours, namely, protactinium and thorium. They all had to leave their old, familiar places in the sixth, fifth and fourth groups, and move into the third.

   Almost one hundred years ago Mendeleyev had moved uranium out of this group. Now it was back in it, but this time with "fuller rights." See what curious things may happen in the life of the Periodic System.

   The physicists agreed to such a state of affairs, but not all the chemists, and not without reserve, because as regards properties uranium is just as much a stranger to Group III as it was in Mendeleyev's time. Nor is the third group quite suitable for thorium and protactinium.

   Where is thy place, uranium? It remains a point of controversy among scientists.

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