A radioactive element, discovered in 1952 by A. Ghiorso and colleagues in residue from a thermonuclear explosion; a member of the ACTINIDE SERIES.

Weighable amounts have since been prepared by neutron bombardment of plutonium.

Basic Properties
Symbol: Es
Atomic number: 99
Atomic weight: {252}
Group name: Actinoid
Period in periodic table: 7 (actinoid)
Block in periodic table: f-block
Ground state electron configuration: Rn.5f¹¹.7s²

Physical Properties
Standard state: solid at 298 K
Colour: unknown, but probably metallic and silvery white or grey in appearance
Molar volume (/cm3): 28.52
Melting point (/K): 1133 or 860 °C (1580°F)