Einsteinium – facts and properties
- Symbol
- Es
- Atomic number
- 99
- Atomic mass
- 252 u
- Period
- 7
- Category
- actinide
- Electron configuration
- [Rn] 5f¹¹ 7s²
- Electronegativity
- 1.3
- Valence electrons
- 13
- State at standard conditions
- solid
- Melting point
- 860 °C
- Discovered
- 1952
Einsteinium is a man-made, radioactive metal with atomic number 99. It was found in 1952 in the fallout of "Ivy Mike", the first test of a hydrogen bomb. The discovery was kept secret at first and published only in 1955. The name recalls Albert Einstein. Only tiny amounts of einsteinium exist, and yet in 2021 a bond length in an einsteinium compound was measured for the first time.
Position in the periodic table
Occurrence and extraction
The first einsteinium did not come from a laboratory but from a nuclear weapons test. In the Ivy Mike test of November 1952 on a Pacific atoll, uranium nuclei captured many neutrons in a flash and turned into heavier elements by beta decay. Researchers in Berkeley, Argonne and Los Alamos examined filter papers that aircraft had collected from the cloud, and later coral material from the atoll. Albert Ghiorso and his team separated tiny amounts of element 99 from it. This was the isotope einsteinium-253, whose half-life is a little over twenty days.
The results stayed under wraps at first. Independently, single atoms of the element had been made in 1954 in a Berkeley cyclotron from uranium and nitrogen ions. The publication appeared in 1955, and the name honours Albert Einstein, who had died in the spring of that year.
Today einsteinium is made in the High Flux Isotope Reactor at Oak Ridge. Curium and californium are irradiated with neutrons for a long time, and californium-252 turns into einsteinium-253 along the way. The yield ranges from micrograms to a few milligrams, and the separation takes place in shielded chambers. The longest-lived isotope, einsteinium-252, has a half-life of a little over a year.
Properties and reactions
Einsteinium is in period 7 and is the eleventh actinoid, in the actinoid row between californium on its left and fermium on its right. Holmium sits above it in the lanthanoid row. The resulting electron configuration is [Rn] 5f¹¹ 7s². The electronegativity of 1.3 is an estimate, and the melting point of 860 °C was measured on tiny samples and is correspondingly uncertain. Its atomic mass is given as 252 u, the mass number of the longest-lived isotope, einsteinium-252.
In compounds plus three is the rule, as for its neighbours. Divalent einsteinium has also been detected, which fits the trend that the divalent state grows in importance towards the end of the actinoid series. Halides and an oxide have been prepared in the smallest quantities. The metal evaporates comparatively easily.
The greatest obstacle is its own radiation. The isotopes decay so fast and with so much energy that a sample heats up and loses its crystal order. Einsteinium-253 also turns into berkelium-249 by alpha decay, and einsteinium-254 into berkelium-250, so a sample keeps changing its composition. Because einsteinium would accumulate in the bones if it entered the body, work is done only in closed, shielded facilities.
Research and synthesis
Outside research there is no use, since the quantities are far too small. Einsteinium did serve as target material for the next discovery: in 1955 researchers bombarded about a billion atoms of einsteinium-253 with alpha particles and thereby made mendelevium.
In 2021 a team at Lawrence Berkeley National Laboratory achieved a breakthrough in measurement. Using X-rays on a sample of less than 250 nanograms of einsteinium-254, it determined for the first time the bond length between an einsteinium ion and the surrounding atoms of a molecule. A nanogram is a billionth of a gram. The sample came from Oak Ridge, and the experiment had to be quick, because the sample was constantly changing through decay.
Such measurements show whether the trends of the actinoids continue to the end of the series, and they give test values for computer models of the heavy elements.
Quick question
What is the atomic number of einsteinium (Es)?
FAQ
Why is einsteinium called einsteinium?
It is named after the physicist Albert Einstein, who died in 1955, the year the discovery was published. Einstein is best known for the theory of relativity.
In what circumstances was einsteinium discovered?
It was found in the fallout of the Ivy Mike test in 1952. Researchers examined filter papers and coral and separated element 99 from them. Because of secrecy, this became known only in 1955.
Does einsteinium have any application?
Only in research. It served as target material for making mendelevium, and with tiny samples one studies how the heaviest actinoids behave chemically.