Atomic number 103

Lawrencium

Lr
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Shells Orbitals 5f 7s 7p

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103 electrons in 7 shells: 2, 8, 18, 32, 32, 8, 3.

Shells are a teaching model: an electron does not travel on a ring at a fixed distance.

Category: Actinide
Period: 7
Block: d
Atomic mass: 266.120 Da (longest-lived isotope, estimated)
Electron configuration: [Rn] 5f¹⁴ 7s² 7p¹
Phase at 25 °C: solid
Melting point: 1627 °C
Electronegativity (Pauling): 1.3
Discovered: March 1961, Albert Ghiorso, Torbjørn Sikkeland, Almon E. Larsh and Robert M. Latimer

Neighbours in the table

No Rf

Boron ions fired at a speck of californium produced element 103 in March 1961. The work took place in California, at Berkeley’s Lawrence Radiation Laboratory, where Albert Ghiorso, Torbjørn Sikkeland, Almon E. Larsh and Robert M. Latimer ran a linear accelerator, in Jefferson Lab’s account. The californium weighed three micrograms, three millionths of a gram, by Jefferson Lab’s figure. It was a blend of californium-249, -250, -251 and -252, struck by boron-10 or boron-11, in Los Alamos’s description. Several isotopes formed, and which one the group actually detected is still unclear, Jefferson Lab adds.

The new element was named after Ernest O. Lawrence, inventor of the cyclotron, according to Los Alamos. PubChem gives the mass of its longest-lived isotope, lawrencium-266, 266.120 Da.

Lawrencium’s configuration is [Rn] 5f¹⁴ 7s² 7p¹ in the Periodic-Table-JSON dataset, with the last electron in a 7p orbital. It puts 14 electrons in the 5f subshell. Its oxidation state, the charge an atom would carry if all its bonds were ionic, is +3 in Jefferson Lab’s and Los Alamos’s data.

Where it is found

Lawrencium has no abundance in the Earth’s crust or in seawater. The total ever produced is tiny, Jefferson Lab reports.

The 1961 atoms were caught in flight. Nuclei formed in the target recoiled into helium and ended up on a thin copper tape, according to Los Alamos. The tape then moved its catch in front of a row of solid-state detectors. These recorded alpha particles, helium nuclei thrown out by a decaying nucleus, with an energy of 8.6 MeV (million electron volts). The signal had a half-life, the time for half of a sample to decay, of 8 seconds.

Longer-lived isotopes followed. Workers at the Dubna Laboratory found lawrencium-256 in 1965, lasting 35 seconds in Los Alamos’s figure and 27.9 seconds in the Atomic Mass Data Center’s. The Data Center dates the first lawrencium-262 to 1987 and lawrencium-266 to 2014.

Why it matters

The 8-second emitter of 1961 was first assigned to lawrencium-257. Several lawrencium isotopes had formed in the target, and which one the Berkeley team detected was unclear, in Jefferson Lab’s account. In 1967 Flerov and colleagues at the Dubna Laboratory reported that they could not find an alpha emitter with that half-life, Los Alamos records. The assignment was then changed to lawrencium-258 or lawrencium-259.

Lawrencium-256 was the isotope used to probe its chemistry. Its decays are 85 per cent alpha emission and 15 per cent positron emission, in which the nucleus throws out a positive electron, in the Data Center’s evaluation. Under 0.03 per cent are spontaneous fission, the nucleus splitting unprompted. In 1968 a Berkeley team used a few of its atoms to test how lawrencium ions behave in solution, Los Alamos reports. Working very fast, they moved the ions from a buffered water solution into an organic solvent, each extraction lasting about 30 seconds.

Lawrencium behaves differently from nobelium, element 102, whose ions are 2+, and more like the 3+ elements earlier in the actinide series, according to Los Alamos. Beyond such experiments the element has no uses outside basic research, because so little of it has ever been made, Jefferson Lab explains.

Properties

Properties of lawrencium Standard atomic weights from IUPAC/CIAAW (abridged, 2024); other values from PubChem's periodic table, kelvin converted to °C.
Property	Value	Unit	Source
Atomic number	103
Atomic mass	266.120 Da	Da	PubChem, longest-lived isotope, estimated
Melting point	1627 °C	°C	Los Alamos: 1627 °C
Electronegativity (Pauling)	1.3
Electron configuration	1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s² 4f¹⁴ 5d¹⁰ 6p⁶ 7s² 5f¹⁴ 7p¹
Phase at 25 °C	solid

This element has no standard atomic weight; the atomic mass shown is that of its longest-lived isotope, as PubChem gives it.

That mass is an estimate by the IAEA's Atomic Mass Data Center, not a measurement.

Safety

Lawrencium has no stable isotope, according to Jefferson Lab, and Haz-Map, in PubChem’s safety record, lists it as a radiation hazard: its decaying atoms give off ionising radiation. There is no everyday form of the element, since only tiny amounts have ever been made. What is known of its hazards is gathered in the PubChem Laboratory Chemical Safety Summary for lawrencium.

Questions

Who is lawrencium named after?

Lawrencium honours Ernest O. Lawrence, the inventor of the cyclotron, according to Los Alamos. The element itself was first made in March 1961 at Berkeley's Lawrence Radiation Laboratory in California, known today as the Lawrence Berkeley Laboratory, Jefferson Lab records.

What is the most stable isotope of lawrencium?

Lawrencium-262 lasts about 4 hours in the evaluation of the International Atomic Energy Agency (IAEA) and in Jefferson Lab's, which calls it the most stable isotope. It decays by electron capture, the nucleus absorbing an electron, to nobelium-262, by alpha emission to mendelevium-258, or by spontaneous fission, which IAEA puts at 10 per cent and the Atomic Mass Data Center below 10. Lawrencium-266 lasts longer: about 22 hours for the Data Center and 11 hours for IAEA, by fission alone.

What is the electron configuration of lawrencium?

Lawrencium's configuration is [Rn] 5f¹⁴ 7s² 7p¹ in the Periodic-Table-JSON dataset, with shells of 2, 8, 18, 32, 32, 8 and 3 electrons. The atom's lowest-energy level is ²P°_1/2 and its first ionisation energy 4.96 electronvolts, according to NIST, the US National Institute of Standards and Technology.

What is lawrencium used for?

Nothing outside basic scientific research. The total amount of lawrencium ever produced is tiny, Jefferson Lab explains, which leaves no room for any practical use. In 1968 a Berkeley team used a few atoms of lawrencium-256 to study how its ions behave, moving them from water into an organic solvent in about 30 seconds each, Los Alamos reports.