Oganesson at a glance
- Atomic number
- 118
- Symbol
- Og
- Atomic mass
- 294 u
- Category
- Noble gas
- Group / period
- 18 / 7
- Electron configuration
- [Rn] 5f 14 6d 10 7s 2 7p 6
- State at 25 °C
- Unknown
- Melting point
- n/a
- Boiling point
- n/a
- Density
- 4.9 g/cm³
- Electronegativity
- n/a
- 1st ionization energy
- 860 kJ/mol
- Oxidation states
- n/a
- Discovered
- 2002
Atomic structure
A neutral oganesson atom has 118 protons and 118 electrons, and its most common isotope carries about 176 neutrons. One atom weighs about 4.88 × 10⁻²⁵ kg, so a mole of oganesson (6.022 × 10²³ atoms) weighs 294 g. That nucleus holds 1.49 neutrons for every proton, typical of heavy nuclei, which need extra neutrons to hold together against the protons' repulsion. The electrons fill 7 shells (K 2, L 8, M 18, N 32, O 32, P 18, Q 8), which gives the configuration [Rn] 5f 14 6d 10 7s 2 7p 6. Its outer shell is full, which is why oganesson hardly reacts with anything. Every isotope is radioactive and short-lived; only a handful of atoms have ever been made, one at a time.
Physical properties
So little oganesson has ever existed at once that its melting point, boiling point and even its state at room temperature are unknown. Its density is 4.9 g/cm³ (predicted), 4.9 times as dense as water.
Chemical behaviour
It has no measured electronegativity, because it almost never forms bonds. Pulling off its outermost electron takes 860 kJ/mol (predicted), less than Radon above it (1037 kJ/mol). Group 18 also holds Helium, Neon, Argon, Krypton, Xenon and Radon, which share its outer-shell pattern. Its Lewis symbol is Og surrounded by 8 dots. Handle with care: as a pure element it is radioactive.
Where it comes from
It does not occur in nature in useful amounts; it is made in nuclear reactors or particle accelerators. It was first made at Dubna, with Lawrence Livermore by fusing californium-249 with calcium-48. Its longest-lived known isotope is Og-294, under a millisecond. It was first identified in 2002, making it the 115th element to be discovered (counting the 11 known since antiquity together).