Lawrencium (Lr)
“The actinide series’ grand finale — named for cyclotron inventor Ernest Lawrence, and its electron arrangement openly breaks the aufbau rule.”
How its electrons are arranged
Computed from the aufbau principle, with known real-world exceptions applied automatically.
Characteristics
- A synthetic actinide and the heaviest member of its series; its longest-lived isotopes, such as Lr-262, decay away within a few hours.
- Breaks the aufbau rule: instead of the expected [Rn]5f¹⁴6d¹7s², the ground-state atom is [Rn]5f¹⁴7s²7p¹ — the final electron leaps into a 7p orbital.
- Its first ionization energy was measured only in 2015 at about 4.96 eV, experimentally confirming that strange 7p¹ arrangement.
- Usually trivalent (Lr³⁺) in solution like its actinide cousins, and made only atom-at-a-time by fusing light ions into californium targets.
No visible sample of lawrencium exists — only short-lived atoms made in accelerators, a few at a time. It is expected to be a silvery, intensely radioactive metal that closes the actinide row, though its appearance is inferred from its actinide relatives rather than ever observed.
Where you meet it
✦ Uses
- Closing the actinide chapter: Lr’s chemistry tests whether the f-block truly ends at element 103 and a new d-block row begins.
- Fundamental atomic physics — the landmark 2015 ionization-energy measurement put relativistic atomic calculations to the test at the table’s edge.
- A stepping stone in decay chains: Lr isotopes appear in the alpha-decay ladders of heavier elements, helping laboratories identify them.
◍ Everyday examples
- The cyclotron — Lawrence’s machine — appears in higher-secondary physics discussions, and element 103 carries its inventor’s name.
- Lawrencium’s rule-breaking configuration features in advanced chemistry lessons about why periodic trends sometimes fail at the table’s edge.
History & name
On 14 February 1961, Albert Ghiorso, Torbjørn Sikkeland, Almon Larsh and Robert Latimer at Berkeley’s Lawrence Radiation Laboratory bombarded a californium target with boron-10 and boron-11 ions from the HILAC accelerator and detected isotopes of element 103. It was named lawrencium after Ernest O. Lawrence, inventor of the cyclotron and founder of that very laboratory. As late as 2015, a Japanese collaboration finally measured lawrencium’s first ionization energy — the last element on the table to give up that secret.