Periodic table › Einsteinium
Einsteinium — Es
Actinoid · Group Actinoid (f-block) · Period 7
Open the 3D atom, orbital and crystal lab →1. Identity and classification
Dense, silvery, radioactive f-block metal that tarnishes rapidly in air
- Name and symbol
- Einsteinium (Einsteinium) · Es
- Atomic number
- 99
- Relative atomic weight / mass number
- [252]
- Group · period · block
- Actinoid (f-block) · 7 · f
- Category
- Actinoid
- State near room temperature
- Solid
- Stable isotopes
- No stable isotopes
- CAS number
- 7429-92-7
Square brackets [A] indicate a representative isotope mass number, not an average atomic weight. Neutron counts differ between isotopes.
2. Atomic structure and electron configuration
- Protons · electrons in a neutral atom
- 99 · 99
- Neutrons in reference isotope
- 153 (252Es)
- Full electron configuration
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁶ 5f¹¹ 7s²- Abbreviated configuration
[Rn]7s² 5f¹¹- Electrons per shell
- 2, 8, 18, 32, 29, 8, 2
- Listed oxidation states
- +3
- Electronegativity
- 1.3 (Pauling)
- First ionization energy
- 619.436 kJ/mol · 6.42 eV
- Electron affinity
- Not established
- Covalent radius
- 165 pm
- van der Waals radius
- 245 pm
Configurations of superheavy elements may include theoretical predictions. Different definitions of atomic radius are not interchangeable.
3. Physical and thermal properties
- Density
- Not established
- Melting point
- 1133 K · 859.85 °C · 1579.73 °F
- Boiling point
- Not established
- Crystal structure
- FCC
- Specific heat
- Not established
- Thermal conductivity
- 10 W/(m·K)
- Enthalpy of fusion
- 9.4 kJ/mol
- Enthalpy of vaporization
- 133 kJ/mol
- Magnetic ordering
- Paramagnetic
- Mohs hardness
- Not established
- Speed of sound
- Not established
Density and structure depend on temperature, pressure and allotrope. 25°C is a room-temperature reference, not STP. Unestablished values are not zero.
4. Chemical behavior and compounds
The +3 state is common in this series, with important element-specific exceptions.
Selected compounds: EsO / Es₂O₃ (Oxide) · EsClₙ (Chloride) · EsFₙ (Fluoride)
Reaction reference
Many members oxidize in air; behavior depends on the element and oxidation state.
Water reactivity varies across this series and with surface conditions.
5. Isotopes
| Isotope | Status | Natural abundance | Half-life |
|---|---|---|---|
| 252Es | Radioactive | — | 471.7 d |
Half-life units: s seconds, m minutes, h hours, d days, Y years. A dash means no natural-abundance value is given, not zero. Listed records are selected ground states; metastable states are distinct.
6. Discovery and occurrence
- Discovery
- 1952 CE
- Scientists associated with discovery
- Albert Ghiorso & Lawrence Berkeley / Los Alamos teams
- Location
- USA (Ivy Mike nuclear test debris)
- Origin
- Synthetic
- Listed crustal abundance
- 0 ppm
Minerals and naming reference
Synthesized in high-flux nuclear reactors (milligram quantities)
Named from scientific/historical roots associated with Einsteinium (Es), discovered or characterized by Albert Ghiorso & Lawrence Berkeley / Los Alamos teams.
7. Applications
Target for synthesizing Mendelevium (Z=101) and probing relativistic 5f electron behavior; ²⁵⁴Es used as calibration marker on Surveyor 5 lunar lander
Detailed applications by field
- everyday
- Target for synthesizing Mendelevium (Z=101) and probing relativistic 5f electron behavior; ²⁵⁴Es used as calibration marker on Surveyor 5 lunar lander
- industry
- Used in actinoid processing, specialized alloys, and chemical manufacturing (Target for synthesizing Mendelevium (Z=101) and probing relativistic 5f electron behavior; ²⁵⁴Es used as calibration marker on Surveyor 5 lunar lander).
- electronics
- Applied in electronic components, semiconductors, or functional coatings where Einsteinium's electronic structure ([Rn] 5f¹¹ 7s²) provides target conductivity.
- medicine
- Restricted to controlled nuclear medicine or fundamental radiochemical research.
- energy
- Utilized in power generation, battery materials, catalysts, or nuclear technology involving Einsteinium.
- aerospace
- High-performance materials, structural alloys, or space instrumentation utilizing Einsteinium.
- agriculture
- Not used in agriculture due to radioactivity or heavy-metal toxicity.
- science
- Spectroscopic standard, crystallography, and quantum chemistry studies of Period 7 f-block elements.
8. Biological role and safety
Hazard depends on the isotope, chemical form, dose and exposure route.
Elemental substances, ions, compounds and radioisotopes can have different health effects. This is an educational reference; laboratory work requires the material safety data sheet and trained supervision.
Biological role reference
Classified as highly radioactive / synthetic in human and biological systems.