Einsteinium

Discovered in the fallout of the first hydrogen bomb, and named for Albert Einstein.

At a glance

Symbol: Es
Atomic number: 99
Mass number of its longest-lived isotope: [252]
Group: none; it sits in the actinide row below the table
Period: 7
Family: actinide
Electron configuration: [Rn] 5f¹¹ 7s²
Electronegativity: 1.30
Common ions: Es³⁺
Isotopes: none are stable; ²⁵²Es lasts longest, about 470 days

On the table

Period 7, in the actinide row set below the main table. The other actinides are tinted, and every cell opens its own article.

Electrons and bonding

Radioactive, like every actinide. It gives up electrons to form positive ions.

Properties

State at 25 °C: solid
What it looks like: silvery, radioactive metal that glows in the dark
Melting point: 860 °C
Boiling point: not known
Density: not measured

Where it is found

Not found in nature; made a few milligrams at a time in high-flux reactors.

Discovery and name

A team led by Albert Ghiorso found it in 1952 in debris from Ivy Mike, the first hydrogen bomb test, on Enewetak Atoll in the Pacific. The discovery stayed secret until 1955, when the element was named after Albert Einstein, who had died that year.

What it is used for

Research only. Einsteinium-253 was the target used to make the first atoms of mendelevium in 1955.

In compounds

Es₂O₃einsteinium oxideEsCl₃einsteinium chloride

Handle with care

So radioactive that its own radiation heats its samples and wrecks their crystal structure.