Lawrencium (Lr)

Lawrencium breaks the pattern every other actinide follows: its outermost electron sits in a 7p orbital rather than the expected 6d, because relativistic effects have pulled the 7p level below the 6d one. That was predicted for decades and confirmed in 2015, when a Japanese team measured lawrencium's first ionisation energy — the lowest of any actinide, and low enough to settle the question — using just a few atoms at a time. It is the last actinide, and on IUPAC's 2021 recommendation it belongs in group 3 alongside lutetium.

Properties

Atomic number

103

Symbol

Lr

Mass number of most stable isotope

[266]

Category

Actinide

Period

7

Block

p-block

Electron configuration

[Rn] 7s² 5f¹⁴ 7p¹

Electrons per shell

2, 8, 18, 32, 32, 8, 3

Oxidation states

+3

Discovered

1961 by Albert Ghiorso and colleagues at Berkeley, with confirming work at Dubna

Electron configuration

Full

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f¹⁴ 7p¹

Noble gas shorthand

[Rn] 7s² 5f¹⁴ 7p¹

Shells

K: 2 · L: 8 · M: 18 · N: 32 · O: 32 · P: 8 · Q: 3

What it is used for

• Research only; no application outside the laboratory

Hazards

• Intensely radioactive; exists only as individual atoms in an accelerator

Anomalous electron configuration: [Rn] 7s² 5f¹⁴ 7p¹ rather than the 6d¹ that periodic position predicts, and that many older tables still print. Melting point, boiling point, density and electronegativity are omitted: no measured values exist. The mass given is the mass number of lawrencium-266, the longest-lived at about 11 hours.

Several physical properties are not listed for lawrencium because no bulk sample has ever existed. Only a handful of atoms have been produced, often with half-lives measured in seconds, so published melting points and densities for elements in this range are calculations rather than measurements. They are omitted rather than presented as observed values.

Neighbours in the table