All practice pages/Interatomic theory/Elements
Element 90, an actinide
Named after the Norse god of thunder, far more abundant than uranium, and a possible fuel for future nuclear reactors.
Period 7, in the actinide row set below the main table. The other actinides are tinted, and every cell opens its own article.
Thorium has 90 electrons, one for every proton, so the atom carries no charge. Below are the same 90 electrons written two ways.
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 6s² 6p⁶ 6d² 7s²
Short form: [Rn] 6d² 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 6d², 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.
Thorium sits in period 7 and has 7 shells. The period number counts the shells.
The outer shell holds 2 electrons. Those are the ones thorium 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.
About three times as abundant in the crust as uranium, found mostly in monazite sands in India, Brazil and elsewhere.
Jöns Jacob Berzelius identified it in 1829 in a black mineral from Norway sent to him by Morten Thrane Esmark, and named it after Thor. In 1898 Marie Curie and Gerhard Carl Schmidt each found that it was radioactive.
Thorium oxide once made gas lantern mantles glow brightly and still goes into heat-resistant ceramics, and thoriated tungsten makes welding electrodes. In a reactor thorium can be turned into uranium-233 fuel, and thorium reactors are being developed in India and China.
Weakly radioactive, and its dust is dangerous to inhale. Old camping lantern mantles and some vintage camera lenses contain thorium.