In 1871, Dimitri Mendeleev presented his periodic table to the world. Many of the current 118 elements were missing, and he left placeholders for those yet to be discovered. Each element has a unique story of scientific discovery.

This week on Reactions, the American Chemical Society is honoring Women's History Month during this International Year of the Periodic Table. And they are sharing the story of two of chemistry's most brilliant and bold women, their paths to elemental discovery and how they changed the world as we know it.