Periodic table: new version warns of elements that are endangered

It is amazing to think that everything around us is made up from just 90 building blocks – the naturally occurring chemical elements. Dmitri Mendeleev put the 63 of these known at the time into order and published his first version of what we now recognise as the periodic table in 1869. In that year, the American civil war was just over, Germany was about to be unified, Tolstoy published War and Peace, and the Suez Canal was opened.