Lr Lawrencium

Quick answerLawrencium (Lr) is an actinide with atomic number 103 and a mass number of 266 (the most stable isotope), in period 7. It was discovered by Albert Ghiorso and colleagues in 1961. It is used for actinide research and studying relativistic effects. Its electron configuration is [Rn] 5f14 7s2 7p1.

Lawrencium is a synthetic actinide named for the inventor of the cyclotron, made a few atoms at a time.

Key facts

Symbol	Lr
Atomic number	103
Atomic mass	[266] — mass number of the most stable isotope
Category	actinide
Group	— (f-block element, no group number)
Period	7
Block	f-block
Electron configuration	[Rn] 5f14 7s2 7p1
Discovered	Albert Ghiorso and colleagues, 1961
Uses	actinide research, studying relativistic effects

Quick quiz

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

1. What is the chemical symbol of Lawrencium?

Ac Pa Th Lr

2. What is the atomic number of Lawrencium?

104 105 103 102

3. Which category does Lawrencium belong to?

actinide alkali metal noble gas halogen

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Keep exploring

• Periodic table — all 118 elements
• Neptunium (Np) — another actinide, atomic number 93
• Plutonium (Pu) — another actinide, atomic number 94
• Americium (Am) — another actinide, atomic number 95
• Curium (Cm) — another actinide, atomic number 96
• Berkelium (Bk) — another actinide, atomic number 97
• Californium (Cf) — another actinide, atomic number 98
• Einsteinium (Es) — another actinide, atomic number 99
• Fermium (Fm) — another actinide, atomic number 100
• Mendelevium (Md) — another actinide, atomic number 101
• Nobelium (No) — another actinide, atomic number 102
• All actinide elements — on the periodic table

Sources & last updated

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

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