Lutetium (Lu)
Lutetium (Lu) is a lanthanide with atomic number 71 and a standard atomic weight of 174.97. At room temperature it is a solid that melts at 1,663 °C and boils at 3,402 °C.
Lutetium key facts
Lutetium at a glance
Identity
| Symbol | Lu |
|---|---|
| Atomic number (Z) | 71 |
| Atomic weight | 174.97 ± 0.01 (CIAAW 2024) |
| Category | Lanthanide |
| Group | — (f-block: lanthanide series) |
| Period | 6 |
| Block | f-block |
| CAS number | 7439-94-3 |
Atomic properties
| Electron configuration | [Xe] 4f14 5d1 6s2 Full: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d1 6s2 |
|---|---|
| Electrons per shell | 2, 8, 18, 32, 9, 2 |
| Oxidation states | +3 Less common: 0, +1, +2 |
| Electronegativity (Pauling) | 1.27 |
| First ionisation energy | 5.426 eV (523.5 kJ/mol) 2nd: 14.13 eV · 3rd: 20.959 eV |
| Electron affinity | 0.34 eV |
| Atomic radius (empirical) | 175 pm |
| Covalent radius | 162 pm |
| Van der Waals radius | 224 pm |
Physical properties
| State at 25 °C | Solid |
|---|---|
| Melting point | 1,663 °C · 3,025.4 °F · 1,936.15 K |
| Boiling point | 3,402 °C · 6,155.6 °F · 3,675.15 K |
| Density | 9.84 g/cm³ |
| Specific heat capacity | 0.154 J/(g·K) |
| Crystal structure | Hexagonal |
Isotopes & abundance
| Natural occurrence | Primordial |
|---|---|
| Radioactive | No |
| Natural isotopes (abundance) | 175Lu 97.401%, 176Lu 2.599% (radioactive) |
| Stable isotopes | 1 |
| Known isotopes | 39 |
| Abundance in Earth's crust | 0.8 mg/kg |
| Abundance in seawater | 0.00000015 mg/L |
Atomic weights: CIAAW Abridged Standard Atomic Weights 2024. Other properties: standard reference compilations, checked October 2026; predicted values are marked.
Lutetium electron configuration
Lutetium has 71 electrons. Written in short form, its ground-state configuration is [Xe] 4f14 5d1 6s2 — the electrons of the noble gas xenon, plus 4f14 5d1 6s2.Written out in full: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d1 6s2.
Discovery and name
1907 — Georges Urbain; independently Carl Auer von Welsbach and Charles James · France / Austria / United States.
Latin Lutetia, Paris.
Known for
The last lanthanide; used in PET-scan detector crystals and as a catalyst. Lutetium-177 is used in targeted cancer therapy.
Isotopes of lutetium
Naturally occurring lutetium is a mix of 2 isotopes. Each has 71 protons; they differ in the number of neutrons:
| Isotope | Protons | Neutrons | Natural abundance | Stability |
|---|---|---|---|---|
| 175Lu | 71 | 104 | 97.401% | stable |
| 176Lu | 71 | 105 | 2.599% | radioactive · half-life 37.01 billion years |
39 isotopes of lutetium are known in our data set (half-lives as published in nuclear data tables).
Lutetium and its neighbours in the lanthanide series
Neighbouring elements in the same f-block series: