Thorium (Th)
“The metal named for the Norse god of thunder — common enough in beach sands, even Bangladesh’s own, to fuel reactors for centuries if the thorium age arrives.”
How its electrons are arranged
Computed from the aufbau principle, with known real-world exceptions applied automatically.
Characteristics
- Electron configuration [Rn] 6d² 7s² — period 7, f-block actinide whose atom refuses 5f electrons entirely; in water it lives almost solely as the Th⁴⁺ ion, among the most stable +4 states of any element.
- Thorium-232, half-life 14,050 million years, outlasts the universe’s own age of 13,800 million years — which is why the primordial thorium of Earth’s birth is still here, faintly alpha-active.
- Fertile, not fissile: it swallows a neutron and transmutes through protactinium-233 into fissile uranium-233 — the heart of the thorium fuel cycle and of India’s three-stage nuclear plan.
- Three to four times as abundant in the crust as uranium; its ore mineral monazite is a dense, heavy sand that rivers and waves wash down and heap on beaches and riverbeds.
A bright silvery metal that slowly dims to grey-black in air, thorium is soft enough to cut and can be drawn into wire and sheet. Its dust can catch fire spontaneously, yet its half-life is so long that a lump of the metal is only faintly warm — a gentle giant among radioactive elements.
Where you meet it
✦ Uses
- Gas-lantern mantles: a knitted “Welsbach mantle” impregnated with about 99% thorium oxide and a pinch of cerium glows dazzling white in a bare flame — the light of the gaslight age, still sold for camping lanterns.
- Thoriated tungsten electrodes for TIG welding hold a rock-steady arc at high current — workshops still prize them even as safer replacements phase in.
- Future nuclear fuel: thorium-232 bred into uranium-233 could power reactors with more abundant ore, less long-lived waste and harder-to-weaponise material — India’s three-stage programme is built on exactly this chemistry.
- Vintage thoriated camera lenses of the 1950s–60s used thorium oxide for extra-bright glass; in collectors’ cabinets those lenses slowly turn amber-brown.
- A cautionary medical relic: the X-ray contrast medium Thorotrast, a thorium dioxide colloid injected into patients in the 1930s–50s, surfaced decades later as cancer — the episode that taught medicine its radiation lesson.
◍ Everyday examples
- The beach sands of Cox’s Bazar and Teknaf in Bangladesh carry monazite among their heavy minerals — the country’s own quietly radioactive thorium store, mapped by the Atomic Energy Commission’s surveys.
- A camping gas lantern bought in Dhaka may still hold a thorium mantle, and its white-hot glow is twentieth-century street lighting reborn.
- Documentary photographs of 1950s city streets lit by hissing gas lamps show the thorium mantle’s pale, brilliant white — an era students meet in history books.
History & name
In 1828 the great Swedish chemist Jöns Jacob Berzelius received a strange heavy black mineral unearthed on the Norwegian island of Løvøya, and from it he identified the oxide of a brand-new element, naming it thorium after Thor, the hammer-wielding Norse god of thunder. For a century it stayed a chemical curiosity — until the Curies’ 1898 radioactivity discoveries revealed thorium itself to be radioactive, and in 1901–02 Ernest Rutherford and Frederick Soddy used thorium to prove that radioactive decay is one element transmuting into another. The dream of thorium-fed reactors grew from the 1950s and lives today in India’s three-stage nuclear programme.