the symbol and atomic number of the heaviest halogen are
Astatine (/ËÃ¦stÉtiËn/ AS-tÉ-teen or /ËÃ¦stÉtÉªn/ AS-tÉ-tin) is a radioactive chemical element with the symbol At and atomic number 85. It occurs on the Earth only as the result of decay of heavier elements, and decays away rapidly, so much less is known about this element than its upper neighbors in the periodic table.