99[252]EsEinsteinium
Einsteinium (Es) — element 99actinide · period 7
Einsteinium is a chemical element with the symbol Es and atomic number 99. It is an actinide in period 7 of the periodic table (the f-block), with a standard atomic mass of [252] u. At room temperature (25 °C) einsteinium is a solid.
💡 Known for: Named after Albert Einstein; it was discovered in the debris of the first hydrogen bomb test in 1952.
# Einsteinium properties
| Symbol | Es |
|---|---|
| Atomic number | 99 |
| Atomic mass | [252] u |
| Category | actinide |
| Group | — (f-block, no group number) |
| Period | 7 |
| Block | f-block |
| Electron configuration | [Rn] 5f¹¹ 7s² |
| Full configuration | 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 5f¹¹ 6s² 6p⁶ 7s² |
| Electrons per shell | 2, 8, 18, 32, 29, 8, 2 |
| Protons / electrons | 99 / 99 |
| State at 25 °C | solid |
| Melting point | 1133 K (859.9 °C, 1579.7 °F) |
| Boiling point | 1269 K (995.9 °C, 1824.5 °F) |
| Density | 8.84 g/cm³ |
| Electronegativity (Pauling) | 1.3 |
| First ionization energy | 6.42 eV |
| Atomic radius | — |
| Discovered | 1952 |
# Electron configuration of einsteinium
The electron configuration of einsteinium is [Rn] 5f¹¹ 7s², written out in full as 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 5f¹¹ 6s² 6p⁶ 7s². Its 99 electrons fill 7 shells as 2, 8, 18, 32, 29, 8, 2, so the outermost shell holds 2 electrons.
# Related elements
CfCaliforniumprevious elementFmFermiumnext elementAcActiniumactinideThThoriumactinidePaProtactiniumactinideUUraniumactinideNpNeptuniumactinidePuPlutoniumactinideAmAmericiumactinideCmCuriumactinide
# Einsteinium FAQ
What is the atomic number of einsteinium?
The atomic number of einsteinium is 99: every einsteinium atom has 99 protons in its nucleus. Its symbol is Es.
What is the atomic mass of einsteinium?
The standard atomic mass of einsteinium is [252] u (the mass number of its longest-lived isotope, since it has no stable isotopes).
What is the electron configuration of einsteinium?
Einsteinium's electron configuration is [Rn] 5f¹¹ 7s² (1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 5f¹¹ 6s² 6p⁶ 7s²), with 2, 8, 18, 32, 29, 8, 2 electrons per shell.
Is einsteinium a metal?
Yes. Einsteinium is an actinide, one of the metals.
What is the melting point of einsteinium?
Einsteinium melts at 1133 K (859.9 °C, 1579.7 °F) and boils at 1269 K (995.9 °C, 1824.5 °F).
What is einsteinium used for / known for?
Named after Albert Einstein; it was discovered in the debris of the first hydrogen bomb test in 1952.