All practice pages/Interatomic theory/Elements
Element 101, an actinide
The first element made and identified one atom at a time, and an American tribute to Dmitri Mendeleev in the middle of the Cold War.
Period 7, in the actinide row set below the main table. The other actinides are tinted, and every cell opens its own article.
Mendelevium has 101 electrons, one for every proton, so the atom carries no charge. Below are the same 101 electrons written two ways.
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 5f¹³ 6s² 6p⁶ 7s²
Short form: [Rn] 5f¹³ 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 5f¹³, 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.
Mendelevium sits in period 7 and has 7 shells. The period number counts the shells.
The outer shell holds 2 electrons. Those are the ones mendelevium 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 atoms at a time in particle accelerators.
Albert Ghiorso, Bernard Harvey, Gregory Choppin, Stanley Thompson and Glenn Seaborg made it in 1955 at Berkeley by bombarding einsteinium with alpha particles, identifying it from just 17 atoms. Naming it after the Russian creator of the periodic table during the Cold War was a notable gesture.
Research only.
Radioactive; it has only ever existed a few atoms at a time.