Lutetium (Lu)

Lutetium is the densest and hardest lanthanide and one of the most expensive elements in routine commercial use, largely because separating it from the others is laborious and demand is small. Lutetium-177 attached to a targeting molecule is one of the more effective radiopharmaceuticals in oncology — it delivers beta radiation to tumour cells while emitting enough gamma to be imaged at the same time. Its full 4f subshell is the reason it is arguably a group 3 transition metal rather than a lanthanide at all, which is the position IUPAC's 2021 review came down on.

Properties

Atomic number

71

Symbol

Lu

Standard atomic weight

174.97 u

Category

Lanthanide

Period

6

Block

d-block

Electron configuration

[Xe] 6s² 4f¹⁴ 5d¹

Electrons per shell

2, 8, 18, 32, 9, 2

Melting point

1,936 K — 1662.8 °C — 3025.1 °F

Boiling point

3,675 K — 3401.8 °C — 6155.3 °F

Density

9.84 g/cm³

Electronegativity

1.27 (Pauling)

Oxidation states

+3

Discovered

1907 by Georges Urbain and Carl Auer von Welsbach, independently

Electron configuration

Full

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹

Noble gas shorthand

[Xe] 6s² 4f¹⁴ 5d¹

Shells

K: 2 · L: 8 · M: 18 · N: 32 · O: 9 · P: 2

What it is used for

• Lutetium oxyorthosilicate crystals in PET scanner detectors
• Lutetium-177 therapy for neuroendocrine and prostate cancer
• Petroleum cracking catalysts
• Lutetium-hafnium dating of very old rock

Filed in the d-block: the 4f subshell is full and the differentiating electron is 5d. Whether lutetium or lanthanum belongs in group 3 is still argued; no group number is assigned here to either.

Neighbours in the table