All practice pages/Interatomic theory/Elements
Element 99, an actinide
Discovered in the fallout of the first hydrogen bomb, and named for Albert Einstein.
Period 7, in the actinide row set below the main table. The other actinides are tinted, and every cell opens its own article.
Einsteinium has 99 electrons, one for every proton, so the atom carries no charge. Below are the same 99 electrons written two ways.
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 5f¹¹ 6s² 6p⁶ 7s²
Short form: [Rn] 5f¹¹ 7s², where [Rn] stands for the 86 electrons radon already has.
That list runs by shell. In the order the subshells fill it reads [Rn] 7s² 5f¹¹, because a subshell fills by its energy, not by its shell number.
The simple form counts electrons shell by shell. The orbital form says which subshell each one sits in: s holds 2, p holds 6, d holds 10 and f holds 14. Shell 4 here is 4s² 4p⁶ 4d¹⁰ 4f¹⁴, and 2 + 6 + 10 + 14 is 32.
Einsteinium sits in period 7 and has 7 shells. The period number counts the shells.
The outer shell holds 2 electrons. Those are the ones einsteinium can lose, gain or share, so they are the ones that decide what it bonds with.
Radioactive, like every actinide. It gives up electrons to form positive ions.
Not found in nature; made a few milligrams at a time in high-flux reactors.
A team led by Albert Ghiorso found it in 1952 in debris from Ivy Mike, the first hydrogen bomb test, on Enewetak Atoll in the Pacific. The discovery stayed secret until 1955, when the element was named after Albert Einstein, who had died that year.
Research only. Einsteinium-253 was the target used to make the first atoms of mendelevium in 1955.
So radioactive that its own radiation heats its samples and wrecks their crystal structure.