ACTINIDES

The Actinides are a set of 15 highly radioactive elements, only 5 of which can be found in nature. We don't recommend the finding thing: Chernobyl. Their atomic numbers range from 89 to 103, which means rather than living in the main body of the Periodic Table, they get their own row, below. Like that one entitled sibling who gets the en-suite. Uranium92 was the heaviest element known to woman: until 1940, when Neptunium was discovered.

You've heard of "Finding a Needle in a Haystack". Now get ready for: "Finding Elements which Don't Occur in Nature". Uranium was discovered in 1789 (Klaproth), and Thorium in 1829 (Berzelius), but most Actinides were (wo)man-made in a lab in the 1900s, when the Industrial Revolution made new technologies available.