Ytterbium is a chemical element with symbol Yb and atomic number 70. It is the fourteenth and penultimate element in the lanthanide series, or last element in the f-block, which is the basis of the relative stability of the 2 oxidation state. However, like the other lanthanides, the 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 m 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.