Timeline of chemical element discoveries Modern discoveries Modern discoveries

| Z | Element_ | Observed_or_predicted | Isolated_widely_known | Observer | First_isolator | Notes_ |
|---|---|---|---|---|---|---|
| 98 | Californium | 1950 |  | S. G. Thompson, K. Street,Jr., A. Ghiorso and G. T. Seaborg (University of California, Berkeley) |  | Bombardment of curium with alpha particles. |
| 99 | Einsteinium | 1952 | 1952 | A. Ghiorso et al. (Argonne Laboratory, Los Alamos Laboratory and University of California, Berkeley) |  | Formed in the first thermonuclear explosion in November 1952, by irradiation of uranium with neutrons; kept secret for several years. |
| 100 | Fermium | 1952 |  | A. Ghiorso et al. (Argonne Laboratory, Los Alamos Laboratory and University of California, Berkeley) |  | Formed in the first thermonuclear explosion in November 1952, by irradiation of uranium with neutrons; kept secret for several years. |
| 101 | Mendelevium | 1955 |  | A. Ghiorso, G. Harvey, R. Choppin, S. G. Thompson and G. T. Seaborg |  | Prepared by bombardment of einsteinium with helium. |