Oganesson

Oganesson (Og), element 118, is the heaviest element on the periodic table today, with a predicted density of about 4.95 g/cm^3 and theoretical placement in the noble-gas group. It can only be made by bombarding a californium target with calcium-48 in a heavy-ion accelerator; a single experiment observes only a few atoms, and every known isotope has a millisecond half-life. It does not occur in nature and cannot be accumulated into a weighable amount, so it has no industrial or civilian use. It exists only as an object of nuclear physics and theoretical chemistry research, used to test the island-of-stability hypothesis in the superheavy region.

Oganesson compounds have never been synthesized and are almost impossible to synthesize. Theoretical calculations predict that relativistic effects may make it less inert than other noble gases, possibly even a solid rather than a gas at room temperature, but these remain paper predictions. Today oganesson exists only as single atoms inside targets and detector systems, forms no separable compound, and enters no product.