Astatine (atomic number 85) is what happens in nature when that naughty radioactive misfit of the actinide series, uranium, decays. The least unstable naturally occurring isotope is 219, with a half life of 0.9 minutes, though that of the artificially created 210 is 8.3 hours. Shell structure is; ground state configuration is Xe.4f14.5d10.6s2.6p5
Fat chance any visible amount will ever be created, making astatine one of the kung-fu space ninjas of the chemical world, leaving chemists puzzling and making half-assed guesses about its chemical properties in its non-existent wake.