 Ytterbium is a chemical element with symbol Yb and atomic number 70 . It is the fourteenth and penultimate element in the lanthanide series , which is the basis of the relative stability of its + 2 oxidation state . However , like the other lanthanides , its most common oxidation state is + 3 , seen in its oxide , halides and other compounds . In aqueous solution , like compounds of other late lanthanides , soluble ytterbium compounds form complexes with nine water molecules . Because of its closed @-@ shell electron configuration , its density and melting and boiling points differ from those of the other lanthanides . 
