Francium
Although chemists knew the element number 87 in the periodic table should exist, it was a long time before it was discovered.  In the early 1900s, nearly all boxes on the periodic table had been filled. Chemists knew that one element had been found to fit into each box. Francium was discovered in 1939 by a French chemist called Marguerite Perey. She named it after her home country, France.