Lutetium (Lu)
Element 71 · Lanthanide · atomic mass 174.97 u · f-block, period 6
Electron shells: 2, 8, 18, 32, 9, 2
Lutetium is the hardest and densest lanthanide and the most expensive to purify. IUPAC now recommends placing it in group 3 rather than lanthanum.
PET scanners "see" using lutetium crystals that flash when a gamma ray hits them.
- Atomic number
- 71
- Atomic mass
- 174.97 u
- Electron configuration
- [Xe] 6s² 4f¹⁴ 5d¹
- Group · period · block
- f-block · 6 · f
- Oxidation states
- +3
- Electronegativity
- 1.27 (Pauling)
- Melting point
- 1,663 °C
- Boiling point
- 3,402 °C
- Density
- 9.84 g/cm³
- State at 20 °C
- Solid
- Appearance
- Silvery-white, hard metal
- Discovered
- Georges Urbain and Carl Auer von Welsbach, 1907
71 protons, and 71 electrons when neutral
IUPAC standard atomic weight
Shown in the strip below the table
What Lutetium is used for
- PET scanner detector crystals
- Petroleum cracking catalysts
- Targeted radionuclide cancer therapy
- Geological age dating
Atomic structure of Lutetium
A neutral lutetium atom has 71 protons and 71 electrons. Its most common isotope carries about 104 neutrons, which is where the mass number 175 comes from. Change the neutron count and you have a different isotope of lutetium; change the proton count and you have a different element entirely.
Those electrons fill shells from the inside out: 2, 8, 18, 32, 9, 2. In orbital notation that is [Xe] 6s² 4f¹⁴ 5d¹. As a f-block element its valence count is variable, which is why it can form compounds in several oxidation states.
3D electron orbitals
See where Lutetium's electrons actually are — a cloud of 26,000 points sampled from the probability density |ψ|², not a cartoon of a lobe.
Where Lutetium sits in the periodic table
Discovery and naming
Lutetium was discovered by Georges Urbain and Carl Auer von Welsbach in 1907. Its name comes from Lutetia, the Roman name for Paris.
Keep exploring
Atomic weight from IUPAC/CIAAW; physical properties from PubChem (US National Library of Medicine). Values that have never been measured are shown as “not measured” rather than estimated.
Related Calculators
Frequently Asked Questions
What is the atomic mass of Lutetium?
The standard atomic weight of Lutetium is 174.97 u, as published by IUPAC's Commission on Isotopic Abundances and Atomic Weights.
How many protons, neutrons and electrons does Lutetium have?
Lutetium has 71 protons, because the atomic number is the proton count and that is what makes an atom Lutetium at all. A neutral Lutetium atom has the same number of electrons, 71. The neutron count varies by isotope; the most common one has about 104, since 175 − 71 = 104.
What is the electron configuration of Lutetium?
The electron configuration of Lutetium is [Xe] 6s² 4f¹⁴ 5d¹. Its electrons are arranged 2, 8, 18, 32, 9, 2 across 6 shells.
Is Lutetium a metal?
Yes. Lutetium is classified as a lanthanide, on the metallic side of the table.
What group and period is Lutetium in?
Lutetium sits in the f-block strip below the main table, in period 6, among the lanthanides. Elements in that strip are not given a group number in the standard 18-column layout.
What is the charge of Lutetium?
Lutetium most commonly forms a 3+ ion. Like most transition metals it has several accessible oxidation states, so the charge depends on the compound.
What is the melting point of Lutetium?
Lutetium melts at 1,663 °C and boils at 3,402 °C. That puts it in the solids at everyday temperatures.
What is Lutetium used for?
PET scanner detector crystals, Petroleum cracking catalysts, Targeted radionuclide cancer therapy, Geological age dating. Lutetium is the hardest and densest lanthanide and the most expensive to purify.
Who discovered Lutetium, and where does its name come from?
Lutetium (Lu) was discovered by Georges Urbain and Carl Auer von Welsbach in 1907. The name comes from Lutetia, the Roman name for Paris.