ElementsWhat is einsteinium?
Einsteinium is a radioactive metal first found in the debris of the first hydrogen bomb test in 1952.
What is einsteinium used for?
Research only.
Where the name comes from
In honour of Albert Einstein.
Key facts
- Symbol
- Es
- Atomic number
- 99
- Atomic mass
- 252.0830 u
- Family
- Actinide
- Period
- 7
- Group
- none (f-block)
- Block
- f
- State at room temperature
- Solid
- Melting point
- 859.9 °C (1,133 K, 1,580 °F)
- Boiling point
- not measured
- Density
- not measured
- Electrons per shell
- 2, 8, 18, 32, 29, 8, 2
- Electron configuration
- [Rn]7s2 5f11
- Common oxidation states
- +3
- Electronegativity (Pauling)
- 1.3
- First ionisation energy
- 6.42 eV
- Electron affinity
- no value
- Atomic radius (van der Waals)
- 245 pm
- Discovered
- 1952
Place in the periodic table
Einsteinium is element number 99. It sits in period 7 (row 7) of the periodic table, in the separate row of actinides drawn below the main table, and belongs to the f-block. Just before it comes californium (98), and just after it comes fermium (100).
Family: Actinides.
Physical properties
At room temperature einsteinium is a solid. Its melting point is about 859.9 °C. Its boiling point has not been measured reliably.
Inside the atom
An atom of einsteinium has 99 protons in its nucleus and, when neutral, 99 electrons around it. The electrons are arranged in 7 shells: 2, 8, 18, 32, 29, 8, 2. The outermost shell holds 2 electrons. Written in full, the electron configuration is [Rn]7s2 5f11.
Its electronegativity on the Pauling scale is 1.3. This number shows how strongly an atom pulls shared electrons towards itself: fluorine, the strongest, is 3.98. Removing one electron from an atom takes 6.42 electronvolts (about 619 kilojoules per mole). One mole of einsteinium weighs 252.0830 grams, so a single gram contains about 2.39 × 1021 atoms.
The ring picture is a simple model that only counts the electrons in each shell. Real atoms do not look like this.
Next steps
- Work out the weight of a compound that contains einsteinium with the molar mass calculator.
- Compare it with every other element in the sortable list.
- Test yourself with the symbol quiz.
Figures on this page are from PubChem (U.S. National Library of Medicine), as downloaded on 11 November 2026. See About and data sources.