I am confused as to why thallium is toxic, while the other members of group 13 are safe? (Quotes are from Wikipedia) Boron - "Elemental boron [is] non-toxic to humans and animals" Aluminum - "... [has] extremely low acute toxicity..." Gallium - "...metallic gallium is not considered toxic..." Indium - "...is not a toxic hazard." Thallium - "Thallium and its compounds are extremely toxic" Why is this the case? It seems that I can touch boron, aluminum, gallium and indium with my bare hands, but not thallium. I don't understand this. Thanks.