Timeline of chemical element discoveries Modern discoveries Modern discoveries

| Z | Element_ | Observed_or_predicted | Isolated_widely_known | Observer | First_isolator | Notes_ |
|---|---|---|---|---|---|---|
| 72 | Hafnium | 1911 | 1922 | G. Urbain and V. Vernadsky | D. Coster and G. von Hevesy | Urbain claimed to have found the element in rare-earth residues, while Vernadsky independently found it in orthite. Neither claim was confirmed due to World War I. After the war, Coster and Hevesy found it by X-ray spectroscopic analysis in Norwegian zircon. Hafnium was the next to last element with stable isotopes to be discovered. |
| 91 | Protactinium | 1913 |  | O.H.Göhring and K. Fajans |  | The two obtained the first isotope of this element that had been predicted by Mendeleev in 1871 as a member of the natural decay of 238U. Originally isolated in 1900 by William Crookes. |
| 43 | Technetium | 1937 | 1937 | C. Perrier and E. Segrè | C. Perrier & E.Segrè | The two discovered a new element in a molybdenum sample that was used in a cyclotron, the first synthetic element to be discovered. It had been predicted by Mendeleev in 1871 as eka-manganese. |