|Isotope||Atomic mass (Da)||Isotopic abundance (amount fraction)|
|159Tb ||158.925 35(2)||1|
Terbium is a monoisotopic element and its atomic weight is determined solely by its isotope 159Tb.
The Commission last revised the standard atomic weight of terbium in 2005 based on the latest Atomic Mass Evaluation by IUPAP.
SOURCE Atomic weights of the elements: Review 2000 by John R de Laeter et al. Pure Appl. Chem. 2003 (75) 683-800
© IUPAC 2003
Ar(Tb) = 158.925 35(2) since 2005
The name derives from the village of Ytterby in Sweden, where the mineral ytterbite (the source of terbium)
was first found. Terbium was discovered by the Swedish surgeon and chemist Carl-Gustav
Mosander in 1843 in an yttrium salt, which he resolved into three elements. He called one yttrium, a
rose-colored salt he called terbium, and a deep-yellow peroxide he called erbium. In 1862, the Swiss
chemist Marc Delafontaine reexamined yttrium and found the yellow peroxide. Because the name erbium
had now been assigned to the rose-colored oxide, he reintroduced the name terbium for the yellow
peroxide. Thus the original names given to erbium and terbium samples are now switched.