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General Chemistry

Einsteinium

Definition and meaning of Einsteinium in chemistry.
Einsteinium is a highly radioactive synthetic element with the symbol Es and atomic number 99. It belongs to the actinide series on the bottom row of the periodic table. Scientists named this metal in honor of the physicist Albert Einstein.
Einsteinium element card: symbol Es, atomic number 99, atomic mass [252], electron configuration [Rn] 5f¹¹ 7s², oxidation states +3, Actinide, f-block, period 7, solid at room temperature.

In more detail

Einsteinium is a soft, silvery metal that evaporates much more easily than other actinide elements. It was first discovered in the radioactive debris of the first thermonuclear bomb explosion in 1952. Today, scientists produce it in tiny amounts by bombarding lighter elements with neutrons.

The element is highly unstable, meaning its isotopes decay very quickly into lighter elements. Einsteinium typically forms a +3 oxidation state in water-based solutions and solid compounds. However, studying the chemistry of einsteinium is extremely difficult for researchers.

The intense radiation released by the metal quickly breaks any chemical bonds it forms. This radiation also damages the metal’s crystal structure and heats it up. The heat is so high that the metal glows with a bright light in the dark.

Students often assume that we know all the basic physical properties of einsteinium. In reality, the rapid self-destruction of the metal makes it impossible to measure its melting point. Because of this heat, the metal can melt itself under its own intense radioactivity.

Only tiny quantities, measured in micrograms, are produced for research each year. This low production makes it one of the rarest materials on our planet.

Key facts

Field
General Chemistry
Symbol
Es
Atomic number
99
Atomic mass
[252] u
Category
Actinide
State at room temperature
Solid
Example
Scientists used the isotope einsteinium-253 as a target material to discover the element mendelevium. They placed a tiny sample of einsteinium inside a particle accelerator and shot alpha particles at it. The nuclear collision added protons to the target, creating the first atoms of mendelevium. This famous experiment showed how researchers can use heavy synthetic elements to make even heavier elements.

Frequently asked questions

Why does einsteinium glow in the dark?

It releases high-energy radiation that continuously heats the metal and excites the surrounding air molecules. This process produces a visible glow that researchers can see in dark rooms.

How was einsteinium first discovered?

Scientists found it in the radioactive ash after the first hydrogen bomb test in the Pacific Ocean. The blast created conditions that forced uranium atoms to absorb many neutrons very quickly.

Can we use einsteinium to build nuclear power plants?

No, its isotopes decay too quickly and are too rare to be used for energy. Scientists only use it as a target to create heavier elements in particle accelerators.

Related terms

Sources & references

By the Chemistry Dictionary editorial team · Reviewed July 17, 2026