Timeline of chemical element discoveries Modern discoveries Modern discoveries

| Z | Element_ | Observed_or_predicted | Isolated_widely_known | Observer | First_isolator | Notes_ |
|---|---|---|---|---|---|---|
| 87 | Francium | 1939 |  | M. Perey |  | Perey discovered it as a decay product of 227Ac. Francium is the last element to be discovered in nature, rather than synthesized in the lab, although some of the synthetic elements that were discovered later (plutonium, neptunium, astatine) were eventually found in trace amounts in nature as well. |
| 85 | Astatine | 1940 |  | R. Corson, R. Mackenzie and E. Segrè |  | Obtained by bombarding bismuth with alpha particles. Later determined to occur naturally in minuscule quantities (<25 grams in earth`s crust). |
| 93 | Neptunium | 1940 |  | E.M. McMillan and H. Abelson |  | Obtained by irradiating uranium with neutrons, it is the first transuranium element discovered. |
| 94 | Plutonium | 1940–1941 |  | Glenn T. Seaborg, Arthur C. Wahl, W. Kennedy and E.M. McMillan |  | Prepared by bombardment of uranium with deuterons. |
| 95 | Americium | 1944 |  | G. T. Seaborg, A. James, O. Morgan and A. Ghiorso |  | Prepared by irradiating plutonium with neutrons during the Manhattan Project. |