Home SCIENCE Thallium Element The Most Toxic Metal On Earth

Thallium Element The Most Toxic Metal On Earth


Today I will tell you about the most toxic metal on earth – about thallium. In the periodic table of chemical elements thallium lies on the bottom of group 13 having an atomic number 81. Let us start off with a little bit of history. Thallium was first discovered in 1861 by an English scientist William Crookes and also simultaneously by a French chemist Claude-Auguste Lamy. It was discovered thanks to the green colour of flames, that compounds of this metal would give.

source/image: Thoisoi2 – Chemical Experiments!

Thallium was discovered when scientists studied rocks containing lead. Nowadays, it is mostly extracted from sulfidic heavy metals, such as crookesite and “gicionite” if my rendering of their names is correct. I’ve got quite old pieces of thallium for my experiment that were produced back in 1970. Since then they have been strongly oxidized and covered in dark thallium oxide. Usually to protect thallium from getting oxidized it is stored in glycerol. Do not worry, we have taken all the necessary precautionary measures.

Do not try this at home! To see the shiny surface of metallic thallium, I submerged my piece of thallium in concentrated nitric acid where it slowly began to dissolve forming nitrites of this metal. Thallium’s oxides have been washed away, the metal looks shiny with bluish shades. Without its oxides this metal can easily be confused with tin or other safe metals that is why thallium is quite treacherous.


It can easily be melt down because its melting point is just 304 degrees Celsius. Molten thallium oxidizes very quickly when exposed to air covering in dark thallium oxide layer. This sets it apart from other metals belonging to group 13. For instance chemical activity of metals starting from aluminium and finishing with indium steadily decreases. Indium doesn’t even oxidise when it is exposed to air and remains shiny.Do not repeat the experiments shown in this video!