Lanthanides and actinides

In addition to lanthanum La, the lanthanides include the 14 elements listed below in the periodic table

Ce Ce
Praseodymium Pr
Neodymium Nd
Promethium Pm
Samarium Sm
Europium Eu
Gadolinium Gd
Terbium Tb
Dysprosium Dy
Holmium Ho
Erbium Er
Thulium Tm
Ytterbium Yb
Lutetium Lu

All are metals and chemically similar.

The actinides include actinium and the 14 following elements in the periodic table:

Thorium Th
Protactinium Pa
Uranium U
Neptunium Np
Plutonium pu
Americium Am
Curium cm
Berkelium Bk
Californium Cf
Einsteinium It
Fermium Fm
Mendelevium Md
Nobelium No.
Lawrencium Lr

All actinides are radioactive metals. The heaviest naturally occurring element is uranium with atomic number 92 (sometimes plutonium (94) is also mentioned as the heaviest naturally occurring element because it can occur in tiny traces through the decay of other elements in rocks).