Radium (Ra)
“The element that glows in the dark — it won Marie Curie two Nobel Prizes and lit a generation’s watch dials, then taught the world radioactivity’s price.”
How its electrons are arranged
Computed from the aufbau principle, with known real-world exceptions applied automatically.
The notes
Characteristics
- Electron configuration [Rn] 7s² — period 7, group 2, s-block, two valence electrons: an alkaline earth metal whose Ra²⁺ chemistry mimics barium and calcium so faithfully that the body lays it into bone in calcium’s place.
- Radium-226, half-life 1600 years, fires alpha particles and gamma rays; one gram of it once defined the curie, the classic unit of radioactivity — early researchers literally measured everything against radium.
- Its decay breathes out radon: a sealed radium source quietly accumulates the noble gas inside — the very pathway by which radon was caught in 1900.
- A sample never sleeps: decay energy keeps it faintly warmer than its surroundings and its salts glow for centuries, while the radiation wrecks whatever container or tissue holds it — Marie Curie’s notebooks are still radioactive in lead-lined boxes today.
A silvery-white metal when freshly cut, it blackens within moments in air — but the world came to know radium through its salts, which glow an eerie pale blue-green in the dark as their radiation excites the surrounding air and crystal. A sealed vial seems to hold trapped moonlight.
Where you meet it
✦ Uses
- Luminous paint: radium mixed with zinc sulfide brushed the glow onto watch, clock and aircraft dials from the 1910s — until the slow deaths of the dial-painting “radium girls” spelled the beginning of the end of the trade.
- Early cancer therapy: sealed radium needles and tubes were implanted beside tumours — “Curie therapy”, the ancestor of modern brachytherapy — before cobalt-60 took over the job.
- Historic quack medicine: tonics like Radithor, “certified radioactive water”, sold glowing health until the 1932 death of steel heir Eben Byers forced regulation.
- Modern medicine’s careful return: the isotope radium-223 (trade name Xofigo) is an approved drug that mimics calcium to home in on prostate-cancer bone metastases, turning the old poison into precision therapy.
◍ Everyday examples
- A grandparent’s glow-in-the-dark watch from the 1950s may still faintly shine — antique dealers warn collectors never to open the dial.
- Marie Curie’s century-old laboratory notebooks are stored in lead boxes at the French national library; readers must sign a health waiver.
- Every uranium ore carries radium through the decay chain — and the Curies’ tonnes-to-a-tenth-of-a-gram shed story is retold in Bangladeshi classrooms whenever radioactivity is taught.
History & name
In December 1898, five months after polonium, Marie and Pierre Curie coaxed a second new element out of the same Bohemian pitchblende — one whose radioactivity, gram for gram, was about a million times that of uranium. They named it radium, “the ray element”, from the Latin radius. To prove it was real, Marie then spent four years in a leaky borrowed shed, boiling tonnes of ore residue in great cauldrons until, in 1902, she held a tenth of a gram of radium chloride — work that helped earn the 1903 Physics Nobel, and after she isolated the pure metal in 1910, the 1911 Chemistry Nobel. A 1920s craze followed, putting radium into luminous paint and quack tonics — until dying factory girls forced the world to respect radioactivity.