Einsteinium (Es)
Actinide · f-block · period 7
Silvery radioactive metal that glows blue; visibly damages its own crystal structure.
Einsteinium (symbol Es) is chemical element number 99, a actinide in the actinide series (f-block), period 7 of the periodic table. Its standard atomic weight is (252) and its electron configuration is [Rn] 5f11 7s2. At room temperature it is a solid, and it is radioactive. Found in the fallout of the first hydrogen bomb test and named after Albert Einstein.
Properties
| Atomic number | 99 |
|---|---|
| Atomic mass | (252) |
| Category | Actinide |
| Block | f-block |
| Group · Period | f-block series · 7 |
| Electron configuration | [Rn] 5f11 7s2 |
| Electrons per shell | 2, 8, 18, 32, 29, 8, 2 |
| State at 25 °C | solid |
| Melting point | 1133 K |
| Boiling point | 1269 K |
| Density | 8.84 g/cm³ |
| Electronegativity (Pauling) | 1.3 |
| Radioactive | Yes — no stable isotope |
| Origin | synthetic |
| Discovered | 1952 · Ghiorso et al. |
Key facts about Einsteinium
- Found in the fallout of the first hydrogen bomb test and named after Albert Einstein.
- So radioactive it glows in the dark and heats itself to a visible glow.
- Its intense radiation tears apart its own chemical bonds as fast as they form.
- Only about a milligram is produced worldwide per year.
What Einsteinium is used for
Research only — it was used as the target to discover mendelevium.
Where it sits in the periodic table
Einsteinium is in the actinide series, period 7, of the f-block. Its electron configuration [Rn] 5f11 7s2 means its outermost shell holds 2 electrons, which is what places it here and explains much of its chemistry. See Einsteinium on the interactive table →
Einsteinium — frequently asked questions
What is Einsteinium used for?
Research only — it was used as the target to discover mendelevium.
Is Einsteinium radioactive?
Yes. Einsteinium has no stable isotope, so every form of it is radioactive.
What is the electron configuration of Einsteinium?
Einsteinium has the electron configuration [Rn] 5f11 7s2, which is 2, 8, 18, 32, 29, 8, 2 electrons per shell.
What group and period is Einsteinium in?
Einsteinium is in the actinide series (f-block), period 7, in the f-block. Its outer shell holds 2 electrons.
Who discovered Einsteinium?
Einsteinium was discovered in 1952 by Ghiorso et al..