Radon (Rn). Diagram of the nuclear composition,electron configuration,chemical data,and valence (outer electron) orbitals of an atom of radon-222 (atomic number: 86),the most stable isotope of this element. The nucleus consists of 86 protons (red) and 136 neutrons (orange). 86 electrons (white) successively occupy available electron shells (rings). Radon is a noble gas in group 18,period 6,and the p-block of the periodic table. It is the only known radioactive gas. Radon-222,produced from the decay chain of uranium or thorium ores,has a half-life of just under 4 days,emitting an alpha particle from its unstable nucleus to form polonium-218 |