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Einsteinium

Element 99 · Actinide

Specimen

Atomic number
99
Atomic mass
[252]
State at room temperature
Solid
Melting point
859.9 °C
Boiling point
Unknown
Density
Unknown
Discovered
1952

Mass number of the longest-lived isotope, from IUPAC.1 Other physical data from PubChem.2

Can I eat it?

In food and water
Radioactive. All einsteinium is radioactive. Reactors make it in milligram amounts only. Its radiation is the main danger. 3

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The atom

Es
ShellElectrons
1 (K) 2
2 (L) 8
3 (M) 18
4 (N) 32
5 (O) 29
6 (P) 8
7 (Q) outermost 2
Total99

Configuration [Rn] 5f¹¹ 7s²

5f ↑ ↓ ↑ ↓ ↑ ↓ ↑ ↓ ↑ ↑ ↑
7s ↑ ↓
A shell diagram: each ring is an electron shell and each dot is one electron. The nucleus holds 99 protons. The outermost shell is shown in red. Electrons do not travel on rings: they fill orbitals, regions where an electron is likely to be found. The boxes are those orbitals for the electrons outside the Rn core, with one arrow per electron.

Related elements

Actinides
Ac Actinium Th Thorium Pa Protactinium U Uranium Np Neptunium Pu Plutonium Am Americium Cm Curium Bk Berkelium Cf Californium Fm Fermium Md Mendelevium No Nobelium Lr Lawrencium

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Sources

  1. 1

    IUPAC Commission on Isotopic Abundances and Atomic Weights (CIAAW), 2024. Radioactive Elements .

    Mass number and half-life of the longest-lived isotope of the 34 elements with no standard atomic weight.

  2. 2

    National Center for Biotechnology Information (PubChem), 2026. Periodic Table of Elements .

    Electron configuration, melting and boiling points, density and discovery year for all 118 elements.

  3. 3

    Royal Society of Chemistry, Periodic Table, 2026. Einsteinium - Element information, properties and uses .

    Reference page; its Biological role and Natural abundance sections are quoted.

    • Einsteinium has no known biological role. It is toxic due to its radioactivity. Natural abundance Einsteinium can be obtained in milligram quantities from the neutron bombardment of plutonium in a nuclear reactor.