Unknown propertiesElement 118 · p-block

Oganesson (Og)

Oganesson (Og), element 118, is a synthetic superheavy element whose chemical properties have not been measured; its most stable known isotope has mass number 294. Only a few atoms have ever been made, so its bulk properties are predictions.

118OgOganesson[294]

Atomic number

118

protons

Atomic weight

[294]

most stable isotope

Melting point

—

Boiling point

—

Density

7 g/cm³

predicted

Electronegativity

—

Pauling scale

State at 25 °C

Unknown

Discovered

2002

Russia (Dubna)

Oganesson at a glance

Identity

Symbol	Og
Atomic number (Z)	118
Atomic weight	[294] mass number of the most stable isotope
Category	Unknown properties
Group	18 — noble gases
Period	7
Block	p-block
CAS number	54144-19-3

Atomic properties

Electron configuration	[Rn] 5f¹⁴ 6d¹⁰ 7s² 7p⁶ Full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 5f¹⁴ 6s² 6p⁶ 6d¹⁰ 7s² 7p⁶
Electrons per shell	2, 8, 18, 32, 32, 18, 8
Electron affinity	0.056 eV
Covalent radius	157 pm

Physical properties

State at 25 °C	Unknown
Density	7 g/cm³ (predicted)

Isotopes & abundance

Natural occurrence	Synthetic
Radioactive	Yes
Most stable isotope	²⁹⁴Og — half-life 0.7 ms
Known isotopes	3

Atomic weights: CIAAW Abridged Standard Atomic Weights 2024. Other properties: standard reference compilations, checked October 2026; predicted values are marked.

Oganesson electron configuration

Oganesson has 118 electrons. Written in short form, its ground-state configuration is [Rn] 5f¹⁴ 6d¹⁰ 7s² 7p⁶ — the electrons of the noble gas radon, plus 5f¹⁴ 6d¹⁰ 7s² 7p⁶.Written out in full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 5f¹⁴ 6s² 6p⁶ 6d¹⁰ 7s² 7p⁶.

As a member of group 18 it has 8 valence electrons in its outer shell (shell 7), which largely decide its chemistry.

5f↑↓↑↓↑↓↑↓↑↓↑↓↑↓

6d↑↓↑↓↑↓↑↓↑↓

7s↑↓

7p↑↓↑↓↑↓

Discovery and name

Discovered

2002 — Joint Institute for Nuclear Research with Lawrence Livermore National Laboratory · Russia (Dubna).

Name

Yuri Oganessian, pioneer of superheavy-element research.

Known for

The heaviest known element; only about five atoms have been detected. Although it sits in group 18, calculations predict a solid that is more reactive than the other noble gases.

Isotopes of oganesson

Oganesson has no stable isotopes and does not occur naturally in significant amounts. Its longest-lived known isotope is:

Isotope	Protons	Neutrons	Half-life
²⁹⁴Og	118	176	0.7 ms

3 isotopes of oganesson are known in our data set (half-lives as published in nuclear data tables).

Oganesson compared with group 18

The other elements in group 18 (noble gases), from top to bottom of the table:

Element	Z	Atomic weight	Melting point	Boiling point	Density	Electronegativity
Helium	2	4.0026	—	-269 °C	0.1786 g/L	—
Neon	10	20.180	-249 °C	-246 °C	0.9002 g/L	—
Argon	18	39.95	-189 °C	-186 °C	1.784 g/L	—
Krypton	36	83.798	-157 °C	-153 °C	3.749 g/L	3
Xenon	54	131.29	-112 °C	-108 °C	5.894 g/L	2.6
Radon	86	[222]	-71 °C	-62 °C	9.73 g/L	2.2
Oganesson	118	[294]	—	—	7 g/cm³ (pred.)	—

Frequently asked questions

4 answers

What is the atomic mass of oganesson?

Oganesson has no stable isotopes, so it has no standard atomic weight. Periodic tables show [294], the mass number of its most stable known isotope.

How many protons, neutrons and electrons does oganesson have?

A neutral oganesson atom has 118 protons and 118 electrons. Its most stable isotope, oganesson-294, has 176 neutrons.

What is the electron configuration of oganesson?

[Rn] 5f¹⁴ 6d¹⁰ 7s² 7p⁶ (in full: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 5f¹⁴ 6s² 6p⁶ 6d¹⁰ 7s² 7p⁶).

Who discovered oganesson?

2002 — Joint Institute for Nuclear Research with Lawrence Livermore National Laboratory (Russia (Dubna)).