99 · Es

Einsteinium

Identified in 1952 in debris from the Ivy Mike test, not in a cyclotron.

Identity

Atomic number: 99
Symbol: Es
Canonical name: Einsteinium
Category: actinide
Group: unassigned
Period: 7
Block: f

Series set apart from the main table. Whether group 3 is lanthanum or lutetium (actinium or lawrencium) is still discussed, so the group is left empty.

Properties

These quantities come from the Periodic Table JSON compilation. They have not yet been checked, one by one, against CIAAW atomic weights or NIST measurements. A value marked estimated is not a measurement.

Atomic mass: [252] No standard atomic weight. The number shown is the conventional mass number used in tables, not a measured mass in u.
Electron configuration: [Rn] 5f11 7s2
Electrons per shell: 2, 8, 18, 32, 29, 8, 2
Standard state: solid
Density: 8.84 g/cm³
Melting point: 1,133 K
Boiling point: 1,269 K
Electronegativity: 1.3 Pauling
First ionization energy: 619 kJ/mol
Electron affinity: -28.6 kJ/mol

Notable isotopes

This summary is not an inventory of every isotope.

Conventional mass number: 252

History

Ivy Mike debris

Identification · confirmed · 1952

Einsteinium is identified in debris from the Ivy Mike thermonuclear test, analyzed at Berkeley. This is not a cyclotron synthesis.

Evidence: Debris from the Ivy Mike test, not an accelerator.

See the element timeline

Etymology

Theme: scientist
Language: allemand
Root: Einstein
Meaning: Albert Einstein

Scientists

Albert Ghiorso

Places and institutions

Berkeley Radiation Laboratory, later Lawrence Berkeley National Laboratory

Enewetak — historical setting : Trust Territory of the Pacific Islands — present country : Marshall Islands Site of the Ivy Mike test, whose debris yielded einsteinium and fermium.