All isotopes of francium decay into astatine, radium, or radon. The isotopes of francium decay quickly into astatine, radium, and radon. Francium is a highly radioactive metal that decays into astatine, radium, and radon. Promethium, polonium, astatine and radon are radioactive, and therefore present radioactive hazards. Technetium, promethium, astatine, neptunium, and plutonium were discovered through synthesis before being found in nature. There are no stable isotopes of astatine. Unlike its lighter congener iodine, evidence for diatomic astatine is sparse and inconclusive. The inclusion of antimony, polonium, and astatine as metalloids has been questioned. The halogens form homonuclear diatomic molecules (not proven for astatine). Five elements are less frequently so classified&colon; carbon, aluminium, selenium, polonium, and astatine. All halogens have been observed as diatomic molecules, except for astatine, which is uncertain. These values exceed those of astatine and the lighter halogens, following periodic trends. The status of polonium and astatine is not settled. Astatine-218 was the first astatine isotope discovered in nature. No astatine fluorides have been discovered yet.