Science / Periodic Table of Elements / Meitnerium (Mt): Atomic number: 109, Atomic mass: 265.9 g.mol -1, Electronegativity: unknown, Density: unknown, Melting point: unknown, Boiling point: unknown, Vanderwaals radius: unknown, Ionic radius: unknown, Isotopes: 1, Discovered by: Heavy Ion Research Laboratory in 1982. Meitnerium is an artificially produced radioactive element. None of meitnerium's chemistry has been researched, but it should resemble other elements of group 9, like iridium. Applications: Meitnerium does not have any known application and little is known about it. Meitnerium in the environment: Meitnerium is not found free in the environment, since it is a synthetic element.