Moscovium

Moscovium, element 115, is a post-transition metal predicted to occupy Group 15 below bismuth, with the electron configuration [Rn] 5f14 6d10 7s2 7p3. Its three 7p valence electrons are split by strong relativistic spin-orbit coupling into two distinct subshells, which is expected to give moscovium a very different chemistry from bismuth despite their formal relationship as homologs. The most stable confirmed isotope, Mc-290, has a half-life of about 650 milliseconds. Moscovium is notable primarily for its role as a stepping stone: when it decays by alpha emission, it produces nihonium-286, giving researchers a secondary route to study element 113.

Moscovium is investigated to understand the nuclear structure of odd-proton superheavy nuclei and to map the alpha-decay systematics that connect elements 115, 113, and their daughters down the decay chain. Each moscovium synthesis run also generates nihonium atoms, making element 115 experiments doubly valuable. Theoretical chemists use moscovium as a benchmark for testing relativistic calculations of 7p-block chemistry, where spin-orbit effects are expected to split chemical behavior in ways with no analogy in the lighter pnictogen elements.

Moscovium was first synthesized in February 2003 at JINR Dubna by Yuri Oganessian and his team in collaboration with scientists from Lawrence Livermore National Laboratory. The experiment bombarded americium-243 targets with calcium-48 beams, producing four atoms of element 115 that were identified through their decay chains. Additional experiments at JINR, GSI, and other facilities over the following decade confirmed and extended the nuclear data. IUPAC and IUPAP formally recognized the discovery in 2015, crediting the Dubna-Livermore collaboration. The name moscovium, honoring Moscow Oblast, the Russian administrative region where JINR is located, was proposed and approved along with the symbol Mc by IUPAC in November 2016.

Moscovium is entirely artificial. No geological, cosmological, or biological process produces or preserves element 115. Its creation requires the precise collision of calcium-48 ions with americium-243 nuclei inside a heavy-ion accelerator, and even under optimal conditions the synthesis cross-section is measured in picobarns, meaning the element is assembled at a rate of atoms per day at best.

No compounds of moscovium have been prepared or isolated. Relativistic quantum chemical calculations predict that the three 7p electrons of moscovium are split into a j = 1/2 pair and a j = 3/2 singlet, fundamentally altering the bonding geometry compared to bismuth. Theoretical work suggests that Mc+ might be more stable than Mc3+, contrary to the trend in lighter pnictogens, and that moscovium monohalides such as McF could exist as stable gas-phase molecules if atom-at-a-time chemistry experiments are ever performed.

• When moscovium decays, it emits an alpha particle and becomes nihonium, meaning every moscovium experiment also creates element 113 — two new elements produced in a single nuclear reaction sequence.
• The calcium-48 beam used to synthesize moscovium is the same projectile that cracked open the superheavy element frontier for the Dubna team, enabling the discoveries of elements 113 through 118 in quick succession.
• Moscovium was made using americium-243, an isotope that does not occur naturally and must itself be produced in nuclear reactors from plutonium-241 over years of neutron irradiation, making the target material nearly as exotic as the element it helps create.
• Element 115 gained brief internet notoriety in the 1980s and 1990s when Bob Lazar claimed it powered alien spacecraft at Area 51 — decades before it was officially synthesized or named, when it was still the unverified unknown element ununpentium.
• The spin-orbit splitting of moscovium's 7p electrons is so large that theoretical chemists treat the two resulting sub-levels almost as separate orbitals, a quantum relativistic effect that has no counterpart anywhere in the chemistry of second- or third-period elements.