All practice pages/Interatomic theory/Elements
Element 91, an actinide
A rare, highly radioactive metal whose name means before actinium, the element it decays into.
Period 7, in the actinide row set below the main table. The other actinides are tinted, and every cell opens its own article.
Protactinium has 91 electrons, one for every proton, so the atom carries no charge. Below are the same 91 electrons written two ways.
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 5f² 6s² 6p⁶ 6d¹ 7s²
Short form: [Rn] 5f² 6d¹ 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 5f² 6d¹, 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.
Protactinium sits in period 7 and has 7 shells. The period number counts the shells.
The outer shell holds 2 electrons. Those are the ones protactinium 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.
One of the rarest natural elements, present in uranium ores at about a third of a gram per ton of uranium.
Kasimir Fajans and Oswald Göhring found a short-lived isotope in 1913 and called it brevium. In 1917 and 1918 Otto Hahn and Lise Meitner, and separately Frederick Soddy and John Cranston, found the long-lived isotope. It was named protoactinium, before actinium, which was shortened to protactinium in 1949.
None outside research. The ratio of protactinium-231 to thorium-230 in ocean sediments helps date them and trace ocean currents of the past.
Highly radioactive and toxic.