Inner transition metal
An inner transition metal (ITM) is one of a group of chemical elements on the periodic table. They are normally shown in two rows below all the other elements. They include elements 57-71 (lanthanides) and 89-103 (actinides). The lanthanides are very similar, and the actinides are all radioactive.
ITMs have three incomplete outermost electron shells and are all metals. In some cases they are quite malleable and ductile. They do not occur in nature (except for the lanthanides thorium and uranium), and are highly unstable.