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Unseptbium, ₀₀Usb

Unseptbium 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 Og ↑ Usb ↓ — unseptunium ← unseptbium → unsepttrium
Electrons per shell	2, 8, 18, 32, 50, 32, 18, 8, 4 (predicted)
Atomic properties
Oxidation states	Template:Infobox element/symbol-to-oxidation-state: Symbol "Usb" not known
Isotopes of unseptbium v e
Template:infobox unseptbium isotopes does not exist
Category: Unseptbium view talk edit | references

Unseptbium (/ˌuːnsɛptbaɪəm/), also called eka-oganesson, dvi-radon, or element 172, is a possible chemical element which has never been found naturally, and there have never been any attempts to synthesise 172. It is not known if this element is possible, as the radioactive instabilities may show that the periodic table ends soon after the island of stability at unbihexium;^[1] but it is likely the second heaviest possible neutral element. Its atomic number is 172, and its atomic symbol is Usb.

The name Unseptbium is a temporary systematic placeholder name made by IUPAC^[2]

Its extreme instability is attributed to its dense nucleus containing 172 protons; it would undergo quick fission in a fraction of a picosecond, smaller than its upper counterpart Oganesson. It falls way outside of the theorised island of stability. It is also theorised that if stable, it can display high record oxidation states.^[3] It also had been predicted to have ranges of somewhat stable isotopes, namely Unseptbium-465 to Unseptbium-486 as the low neutron band, and Unseptbium-563 to Unseptbium-582. However, the most theoretically stable Unseptbium could get is if it has 318 Neutrons, also known as Unseptbium-490. This isotope would theoretically feature a completely closed spherical neutron shell, possessing a significantly higher barrier against spontaneous fission compared to its immediate neighbours, Unseptbium-489 and Unseptbium-490, as stated in arXiv reports.

1. ↑ Seaborg, Glenn T. (c. 2006). "transuranium element (chemical element)". Encyclopædia Britannica. Retrieved 2010-03-16.
2. ↑ "Element names >100". iupac.qmul.ac.uk. Retrieved 2026-06-13.
3. ↑ Pyykkö, Pekka (2010-12-08). "A suggested periodic table up to Z ≤ 172, based on Dirac–Fock calculations on atoms and ions". Physical Chemistry Chemical Physics. 13 (1): 161–168. doi:10.1039/C0CP01575J. ISSN 1463-9084.