Lutetium is a silvery-white, hard lanthanide metal. It is the heaviest and one of the rarest rare-earth elements, occurring in minerals like monazite and xenotime. It is used in catalysts, PET scan detectors (Lu-based scintillators), and high-refractive-index glass.
The ground-state electron configuration of lutetium is [Xe] 4f14 5d1 6s2. This configuration marks the completion of the 4f subshell, distinguishing Lu as the final element in the lanthanide series. The 4f shell is fully filled, giving it unique chemical and physical properties compared to earlier lanthanides.
Lutetium completes the filling of the 4f orbital (4f14), and its chemistry shows a transition between lanthanides and transition metals. Some classifications also group Lu with the d-block elements because it has a 5d1 electron, but it is generally regarded as the final member of the lanthanide series.
Lutetium primarily exhibits the +3 oxidation state (Lu3+), which is very stable and common across its compounds, such as Lu2O3 and LuCl3. The +2 state is extremely rare and unstable, observed only in certain organometallic or low-temperature matrix conditions.
Important applications include:
Lutetium-177 (Lu-177) is a radioactive isotope used in targeted radiotherapy. It emits beta particles that destroy cancer cells while minimizing damage to surrounding tissues. Lu-177 is used in treating neuroendocrine tumors and prostate cancer through drugs like Lutetium Lu-177 dotatate.
Lutetium is less reactive than earlier lanthanides due to its small ionic radius and higher ionization energy. It forms colorless salts and reacts slowly with oxygen and water:
\(\mathrm{4\,Lu(s) + 3\,O_2(g) \rightarrow 2\,Lu_2O_3(s)}\)
\(\mathrm{2\,Lu(s) + 6\,H_2O(l) \rightarrow 2\,Lu(OH)_3(s) + 3\,H_2(g)}\)
Lutetium is scarce because it occurs only in trace amounts within rare-earth minerals like monazite and xenotime. It is difficult to separate from other rare-earth elements due to very similar chemical behavior. Its abundance in the Earth's crust is roughly 0.5 ppm.
Lutetium is a hard, dense, and silvery-white metal with a melting point of about 1663 °C and a boiling point near 3402 °C. It has the highest density and highest melting point among the lanthanides. These properties make it valuable for specialized high-temperature and high-strength materials.
Lutetium(III) compounds are typically colorless or white because Lu3+ has a completely filled 4f subshell (4f14), resulting in no f–f electronic transitions that cause visible absorption.
Natural lutetium consists mainly of stable isotope 175Lu and a trace of 176Lu, which is weakly radioactive (half-life ≈ 3.8 × 1010 years). Lutetium compounds have low toxicity, but fine powders should be handled with care to avoid inhalation or skin irritation.
When lutetium reacts with hydrochloric acid, it forms lutetium(III) chloride and hydrogen gas:
\(\mathrm{2\,Lu(s) + 6\,HCl(aq) \rightarrow 2\,LuCl_3(aq) + 3\,H_2(g)}\)
This reaction demonstrates the typical trivalent chemistry of lutetium.