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Lawrencium is a synthetic chemical element; it has symbol Lr (formerly Lw) and atomic number 103. It is named in honor of Ernest Lawrence, inventor of the cyclotron, a device that was used to discover many artificial radioactive elements. A radioactive metal, lawrencium is the eleventh transuranic element and the last member of the actinide series. Like all elements with atomic number over 100, lawrencium can only be produced in particle accelerators by bombarding lighter elements with charged particles. Fourteen isotopes of lawrencium are currently known; the most stable is 266Lr with half life 11 hours, but the shorter lived 260Lr (half life 2.7 minutes) is most commonly used in chemistry because it can be produced on a larger scale. Chemistry experiments confirm that lawrencium behaves as a heavier homolog to lutetium in the periodic table, and is a trivalent element. It thus could also be classified as the first of the 7th period transition metals. Its electron configuration is anomalous for its position in the periodic table, having an s2p configuration instead of the s2d configuration of its homolog lutetium. However, this does not appear to affect lawrencium's chemistry. In the 1950s, 1960s, and 1970s, many claims of the synthesis of lawrencium of varying quality were made from laboratories in the Soviet Union and the United States. The priority of the discovery and therefore the name of the element was disputed between Soviet and American scientists. The International Union of Pure and Applied Chemistry (IUPAC) initially established lawrencium as the official name for the element and gave the American team credit for the discovery; this was reevaluated in 1997, giving both teams shared credit for the discovery but not changing the element's name.

Superheavy element

In 1949, Glenn T. Seaborg, who devised the actinide concept, predicted that element 103 (lawrencium) should be the last actinide and that the |Lr(3+) ion should be about as stable as |Lu(3+) in aqueous solution. It was not until decades later that element 103 was finally conclusively synthesized and this prediction was experimentally confirmed. 1969 studies on the element showed that lawrencium reacts with chlorine to form a product that was most likely the trichloride, |LrCl3. Its volatility was found to be similar to the chlorides of curium, fermium, and nobelium and much less than that of rutherfordium chloride. In 1970, chemical studies were performed on 1500 atoms of 256Lr, comparing it with divalent (No, Ba, Ra), trivalent (Fm, Cf, Cm, Am, Ac), and tetravalent (Th, Pu) elements. It was found that lawrencium coextracted with the trivalent ions, but the short half life of 256Lr precluded a confirmation that it eluted ahead of |Md(3+) in the elution sequence. In the molecule lawrencium dihydride (|LrH2), which is predicted to be bent, the 6d orbital of lawrencium is not expected to play a role in the bonding, unlike that of lanthanum dihydride (|LaH2). |LaH2 has La–H bond distances of 2.158 Å, while |LrH2 should have shorter Lr–H bond distances of 2.042 Å due to the relativistic contraction and stabilization of the 7s and 7p orbitals involved in the bonding, in contrast to the core like 5f subshell and the mostly uninvolved 6d subshell. In general, molecular |LrH2 and LrH are expected to resemble the corresponding thallium species (thallium having a 6s26p1 valence configuration in the gas phase, like lawrencium's 7s27p1) more than the corresponding lanthanide species. The electron configurations of |Lr(+) and |Lr(2+) are expected to be 7s2 and 7s1 respectively. However, in species where all three valence electrons of lawrencium are ionized to give at least formally the |Lr(3+) cation, lawrencium is expected to behave like a typical actinide and the heavier congener of lutetium, especially because the first three ionization potentials of lawrencium are predicted to be similar to those of lutetium. Hence, unlike thallium but like lutetium, lawrencium would prefer to form |LrH3 than LrH, and LrCO is expected to be similar to the also unknown LuCO, both metals having valence configuration σ2π1 in their monocarbonyls. The pπ–dπ bond is expected to be seen in |LrCl3 just as it is for |LuCl3 and more generally all the |LnCl3. The complex anion |[Lr(C5H4SiMe3)3](−) is expected to be stable with a configuration of 6d1 for lawrencium; this 6d orbital would be its highest occupied molecular orbital. This is analogous to the electronic structure of the analogous lutetium compound.

Lawrencium has three valence electrons: the 5f electrons are in the atomic core. In 1970, it was predicted that the ground state electron configuration of lawrencium was [Rn]5f146d17s2 (ground state term symbol 2D3/2), per the Aufbau principle and conforming to the [Xe]4f145d16s2 configuration of lawrencium's lighter homolog lutetium. But the next year, calculations were published that questioned this prediction, instead expecting an anomalous [Rn]5f147s27p1 configuration. more recent studies and calculations confirm the s2p suggestion. 1974 relativistic calculations concluded that the energy difference between the two configurations was small and that it was uncertain which was the ground state. Although some alkali metal like behaviour has been predicted, adsorption experiments suggest that lawrencium is trivalent like scandium and yttrium, not monovalent like the alkali metals. A lower limit on lawrencium's second ionization energy (>13.3 eV) was experimentally found in 2021. Even though s2p is now known to be the ground state configuration of the lawrencium atom, ds2 should be a low lying excited state configuration, with an excitation energy variously calculated as 0.156 eV, 0.165 eV, or 0.626 eV. However, shorter lived isotopes are usually used in chemical experiments because 266Lr currently can only be produced as a final decay product of even heavier and harder to make elements: it was discovered in 2014 in the decay chain of 294Ts. All other known lawrencium isotopes have half lives under 5 minutes, and the shortest lived of them (251Lr) has a half life of 24.4 milliseconds. The half lives of lawrencium isotopes mostly increase smoothly from 251Lr to 266Lr, with a dip from 257Lr to 259Lr. The two heaviest and longest lived known isotopes, 264Lr and 266Lr, can only be produced at much lower yields as decay products of dubnium, whose progenitors are isotopes of moscovium and tennessine. Both 256Lr and 260Lr have half lives too short to allow a complete chemical purification process. Early experiments with 256Lr therefore used rapid solvent extraction, with the chelating agent thenoyltrifluoroacetone (TTA) dissolved in methyl isobutyl ketone (MIBK) as the organic phase, and with the aqueous phase being buffered acetate solutions. Ions of different charge (+2, +3, or +4) will then extract into the organic phase under different pH ranges, but this method will not separate the trivalent actinides and thus 256Lr must be identified by its emitted 8.24 MeV alpha particles. More recent methods have allowed rapid selective elution with α HIB to take place in enough time to separate out the longer lived isotope 260Lr, which can be removed from the catcher foil with 0.05 M hydrochloric acid.