<Dl> <Dd> <Ul> <Li> Bismuth has the longest half life of any naturally occurring element; its only primordial isotope, bismuth - 209, was found in 2003 to be slightly radioactive, decaying via alpha decay with a half life more than a billion times the estimated age of the universe . Prior to this discovery, bismuth - 209 was thought to be the heaviest naturally occurring stable isotope; this distinction now belongs to lead - 208 . </Li> </Ul> </Dd> </Dl> <Dd> <Ul> <Li> Bismuth has the longest half life of any naturally occurring element; its only primordial isotope, bismuth - 209, was found in 2003 to be slightly radioactive, decaying via alpha decay with a half life more than a billion times the estimated age of the universe . Prior to this discovery, bismuth - 209 was thought to be the heaviest naturally occurring stable isotope; this distinction now belongs to lead - 208 . </Li> </Ul> </Dd> <Ul> <Li> Bismuth has the longest half life of any naturally occurring element; its only primordial isotope, bismuth - 209, was found in 2003 to be slightly radioactive, decaying via alpha decay with a half life more than a billion times the estimated age of the universe . Prior to this discovery, bismuth - 209 was thought to be the heaviest naturally occurring stable isotope; this distinction now belongs to lead - 208 . </Li> </Ul> <Li> Bismuth has the longest half life of any naturally occurring element; its only primordial isotope, bismuth - 209, was found in 2003 to be slightly radioactive, decaying via alpha decay with a half life more than a billion times the estimated age of the universe . Prior to this discovery, bismuth - 209 was thought to be the heaviest naturally occurring stable isotope; this distinction now belongs to lead - 208 . </Li>

Who classified the elements first time in three groups metal non metal metalloids