Unsepttrium

Unsepttrium (/ˌuːnsɛptriəm/), also known as dvi-francium or element 173, is a possible chemical element which has not been observed to occur naturally, nor has it yet been made. Due to instabilities, it is not known if this element is possible, as the instabilities may hint that the periodic table ends soon after the island of stability at unbihexium; however, if possible, it is likely the heaviest possible neutral element. Its atomic number is 173 and its atomic symbol is Ust.

Unsepttrium,  ₁₇₃Ust

General properties
Unsepttrium in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson Template:Periodic table (32 columns, micro)/119+ Uue ↑ Ust ↓ (Bbs) unseptbium ← unsepttrium → unseptquadium
Atomic number (Z)	173
Group	n/a
Period	period 9
Block	s-block
Electrons per shell	2, 8, 18, 32, 50, 33, 18, 8, 4 (predicted)
Physical properties
Phase at STP	Ust:
Atomic properties
Oxidation states
Other properties
Natural occurrence	Ust:
Main isotopes of unsepttrium
Iso­tope Abun­dance Half-life (t1/2) Decay mode Pro­duct 512Ust syn

The name unsepttrium is a temporary IUPAC systematic element name.

Significance

Although Richard Feynman noted that a simplistic interpretation of the relativistic Dirac equation runs into problems with electron orbitals at Z > 1/α = 137, suggesting that neutral atoms cannot exist beyond untriseptium, and that a periodic table of elements based on electron orbitals breaks down at this point, a more thorough analysis calculates the limit to be Z ≈ 173, meaning that neutral atoms most likely cannot exist with atomic number greater than 173. This makes unsepttrium theoretically the heaviest neutral element possible.

Unsepttrium Media

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  Pekka Pyykkö's 172-element (extended) periodic table.

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  Kulsha's first suggested form

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  Kulsha's second suggested form

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  Energy eigenvalues (in eV) for the outermost electrons of elements with Z = 100 through 172, predicted using Dirac–Fock calculations. The − and + signs refer to orbitals with decreased or increased azimuthal quantum number from spin–orbit splitting respectively: p− is p1/2, p+ is p3/2, d− is d3/2, d+ is d5/2, f− is f5/2, f+ is f7/2, g− is g7/2, and g+ is g9/2.

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  Energy eigenvalues for the 1s, 2s, 2p1/2 and 2p3/2 shells from solutions of the Dirac equation (taking into account the finite size of the nucleus) for Z = 135–175 (–·–), for the Thomas-Fermi potential (—) and for Z = 160–170 with the self-consistent potential (---).

Related pages

• untriseptium