Lu Lutetium

Quick answerLutetium (Lu) is a lanthanide with atomic number 71 and an atomic mass of 174.97 (2023), in period 6. It was discovered by Georges Urbain in 1907. It is used for PET scan detectors and cancer therapy. Its electron configuration is [Xe] 4f14 5d1 6s2.

Lutetium is the hardest, densest lanthanide, and its crystals detect cancers in PET scanners used by hospitals.

Key facts

Symbol	Lu
Atomic number	71
Atomic mass	174.97 (IUPAC standard atomic weight, 2023)
Category	lanthanide
Group	— (f-block element, no group number)
Period	6
Block	f-block
Electron configuration	[Xe] 4f14 5d1 6s2
Discovered	Georges Urbain, 1907
Uses	PET scan detectors, cancer therapy, catalysts, lasers, high-refractive glass

Quick quiz

Three questions from the facts on this page. No sign-up, no score is saved.

1. What is the chemical symbol of Lutetium?

Lu Ce La Pr

2. What is the atomic number of Lutetium?

73 72 70 71

3. Which category does Lutetium belong to?

alkali metal halogen lanthanide noble gas

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Keep exploring

• Periodic table — all 118 elements
• Promethium (Pm) — another lanthanide, atomic number 61
• Samarium (Sm) — another lanthanide, atomic number 62
• Europium (Eu) — another lanthanide, atomic number 63
• Gadolinium (Gd) — another lanthanide, atomic number 64
• Terbium (Tb) — another lanthanide, atomic number 65
• Dysprosium (Dy) — another lanthanide, atomic number 66
• Holmium (Ho) — another lanthanide, atomic number 67
• Erbium (Er) — another lanthanide, atomic number 68
• Thulium (Tm) — another lanthanide, atomic number 69
• Ytterbium (Yb) — another lanthanide, atomic number 70
• All lanthanide elements — on the periodic table

Sources & last updated

• CIAAW — Standard Atomic Weights
• PubChem Periodic Table
• Wikipedia — Timeline of chemical element discoveries
• Wikipedia — Lutetium

Last updated: 2026-11-12. Figures are shown with their year; where sources disagree, the value is left out rather than estimated.