Noun
(chemistry) a series of 15 radioactive elements with increasing atomic numbers from actinium to lawrencium
Source: WordNetClick here for more information. main infobox Fermium is a synthetic element with symbol Fm and atomic number 100. It is a member of the actinide series. Source: Internet
It was also pointed out that the actinide contraction at the end of the actinide series was larger than the analogous lanthanide contraction, with the exception of the last actinide, lawrencium: the cause was speculated to be relativistic effects. Source: Internet
This convention is entirely a matter of aesthetics and formatting practicality; a rarely used wide-formatted periodic table inserts the lanthanide and actinide series in their proper places, as parts of the table's sixth and seventh rows (periods). Source: Internet