What chemical element, atomic number 99, is named after Albert Einstein?

The chemical element with atomic number 99, named after Albert Einstein, is einsteinium. Its chemical symbol is Es.

Einsteinium is a synthetic, radioactive element in the actinide series and is the seventh transuranium element. It was first identified in debris from the 1952 Ivy Mike thermonuclear test, although the discovery remained classified during the early Cold War. The element was later produced in laboratories by irradiating heavy elements such as plutonium or californium.

The Berkeley team that received recognition for the discovery proposed names honoring Einstein and Enrico Fermi. Element 99 became einsteinium, while element 100 became fermium. The names were publicly announced at the first Geneva Atomic Conference in 1955. Einstein himself had no role in discovering or studying the element.

A frequent mix-up is with fermium, which is also named for a famous physicist and sits immediately after einsteinium in the periodic table. Einsteinium has no practical everyday use: its scarcity, intense radioactivity, and short-lived isotopes make it primarily useful for nuclear and chemical research.