What are the inner transition elements?
There are two inner transition series. They fit into the periodic table in periods 6 and 7, right after lanthanum and actinium. The first series is called the lanthanide series after lanthanum and the second series is called the actinide series after actinium, the elements that precede them. None of the actinide elements have been found in nature. They are all artificial. All of the elements in the actinide series are radio active.