Among halogens, only Astatine is a radioactive element.
Astatine is a highly radioactive element, and it is the heaviest known halogen. Its chemical properties are believed to be similar to those of iodine. The total amount of astatine in the earth’s crust at any particular time is less than 30 grams, and only a few micrograms have ever been artificially produced. This, together with its short lifetime, leaves no reason for considering the effects of astatine on human health. Astatine is the least reactive and has the most metallic properties of any element in the halogen group.
- Atomic number (number of protons in the nucleus): 85
- Atomic symbol (on the periodic table of elements): At
- Atomic weight (average mass of the atom): 210
- Density: approximately 4 ounces per cubic inch