Einsteinium was first identified in material from a thermonuclear test and can be produced in specialized reactors. It is a radioactive research element with no assigned standard atomic weight. Its identification illustrates how chemical separation and nuclear measurements reveal an element present in extremely small amounts.
FROM ELEMENT TO APPLICATION
AN ELEMENT IN CONTEXT
How did einsteinium enable an experiment without proving its product identity?
Einsteinium target material in mendelevium discovery
FOLLOW THIS RELATIONSHIP
Identify the research input
Einsteinium served as target material in the mendelevium discovery work. This establishes its enabling role while keeping the starting element separate from the proposed product.
Explore the model (optional)
EsFORM → INTERACTION → CONSEQUENCE
Follow the explanation in either direction. These are authored steps, not a physical clock.
Optional: check your understanding
USE THE EXPLANATION
Which statement separates enabling material from identification evidence?
Atomic identity, reference properties and structure models
INTERACTIVE 3D99 visible sites
An electron censusDrag to rotate · scroll or pinch to zoom
[Rn] 5f11 7s2. Grouping electrons by principal shell connects the neutral-atom configuration to periodic-table patterns.
What this representation means
A three-dimensional counting diagram. Dots are count markers, not measured electron positions; spherical placement and spacing are arbitrary. There are no electron trajectories here. Orbitals describe quantum states.
Einsteinium was identified in material collected after the 1952 Ivy Mike thermonuclear test. Its name honors Albert Einstein, not a direct role in the discovery. The early evidence came from nuclear products and chemical separation. Decades later, a 2021 study measured a bond distance in an einsteinium complex, showing how recognizing an element can precede detailed molecular knowledge by generations of experimental work.
1952
Discovery
Scientists identify element 99 in material from the Ivy Mike test.
2021
Bond distance measured
Researchers report structural and spectroscopic measurements of an einsteinium complex.
Einsteinium is manufactured for research and does not occur as a natural resource. Only very small quantities of suitable are available to chemical studies. changes both the amount and composition of a sample, so the calendar becomes part of experimental design as well as a historical record.
Einsteinium compounds allow researchers to examine bonding near the heavy end of the actinides. A measured bond distance and spectroscopic signals provide evidence beyond its place in a periodic table. Its radioactive scarcity limits characterization, so isolated experimental findings should not be inflated into a complete catalog of bulk material properties.
Each section links its supporting references. Descriptions and diagrams were authored for this atlas. Source checks completed. Source checks dated 2026-09-06.
CITE THIS PAGE
Family labels and the group-3 layout are teaching conventions. A table position does not establish an unknown bulk property. Electronic configurations refer to neutral atoms; ions and material environments require their own account.
Read each reference property together with its units, conditions and the reference information below.
Not yet recorded: electron affinity, second ionization energy, ground-state term symbol, van der waals radius, thermal conductivity, specific heat capacity, electrical resistivity, crystal structure, lattice parameter a, space group, abundance in seawater, abundance in the universe, annual production, supply-risk listing, hazard classification, biological role, cas registry number, pubchem cid, wikidata item. These families are declared and awaiting an ingestion run against the source each names; they are listed here rather than shown as empty rows.
Physical
Intended reference: CRC Handbook of Chemistry and Physics · CRC Press
Phase at 20 °C
solid
293.15 K, 101.325 kPa
Melting point in K
1133 K
at standard pressure unless noted
Boiling point
Not recorded
101.325 kPa
Density
Not recorded
solids and liquids at 293 K; gases at 273 K and 101.325 kPa
Atomic and electronic
Intended reference: Pauling electronegativity scale · Widely tabulated; original in The Nature of the Chemical Bond
Electronegativity in Pauling
1.3 Pauling
Pauling scale
First ionization energy in kJ/mol
619 kJ/mol
gas-phase neutral atom, ground state
Covalent radius
Not recorded
single-bond covalent radius
Common oxidation states
+3
states met in ordinary compounds; not exhaustive
Occurrence and identity
Intended reference: CRC Handbook of Chemistry and Physics · CRC Press
Abundance in the crust
Not recorded
upper continental crust, mass fraction
Has stable isotopes
Noderived
Discovery year in CE
1952 CEderived
WHERE IT SITS AMONG ITS NEIGHBORS
Electronegativity across period 7
Es 1.3 Pauling · Einsteinium
Electronegativity across period 7. Exact values.
Ra
0.9
Ac
1.1
Th
1.3
Pa
1.5
U
1.38
Np
1.36
Pu
1.28
Am
1.13
Cm
1.28
Bk
1.3
Cf
1.3
Es
1.3
Fm
1.3
Md
1.3
No
1.3
Lr
1.3
The trend uses the same reference-property values as the periodic table. Elements with no recorded value are left out of the line rather than drawn at zero.
