Astatine comes after Iodine in group 7 of the periodic table.
Mendeleev famously left a space for it when he put his periodic table together. The Guinness Book of World Records has called Astatine the rarest element on Earth. At any one time there is less than 25g of it present.
It was first produced in 1940 at the University of California by Emilio Serge by bombarding Bismuth with Helium ions (He2+). The stalest isotope of Astatine has a half life of 8.3 hours.
Astatine is Greek for unstable!