Gadolinium (Gd)
“The metal whose magnetism switches off just above room temperature — and the injection that makes tumours light up on an MRI scan.”
How its electrons are arranged
Computed from the aufbau principle, with known real-world exceptions applied automatically.
Characteristics
- Electron configuration [Xe] 4f⁷ 5d¹ 6s² — a famous exception to plain Aufbau filling: instead of the expected 4f⁸ 6s², gadolinium keeps a stable half-filled 4f⁷ shell and parks its extra electron in 5d.
- Cooled below about 20 °C it turns ferromagnetic; warmed a few degrees above room temperature that order dissolves into strong paramagnetism — its Curie point is the closest of any element to everyday temperatures.
- The isotope gadolinium-157 swallows slow neutrons more greedily than any other stable nuclide in nature — precisely why nuclear engineers keep it close.
- Free Gd³⁺ ions are toxic to the human body, so medicine only ever injects gadolinium wrapped inside claw-shaped chelate molecules the kidneys can safely flush out.
A silvery-white, ductile metal that keeps a reasonably bright surface compared with the more reactive lanthanides. It is noticeably heavy for a rare earth, and freshly cut pieces gleam before slowly dulling in air.
Where you meet it
✦ Uses
- MRI contrast dye: a gadolinium chelate injected into a vein makes tumours, blood vessels and inflamed tissue glow brightly on the scan.
- Neutron control in nuclear reactors — gadolinium oxide control rods and burnable poisons that tame the chain reaction, plus emergency shutdown chemicals.
- Phosphors and scintillators that convert X-rays into visible light in some radiography detector screens.
- Magnetocaloric research alloys — prototype magnetic refrigerators that chill by magnetism, since gadolinium warms and cools sharply in changing fields.
◍ Everyday examples
- A patient sent for a contrast MRI at a city hospital almost certainly owes the bright, readable image to gadolinium.
- Older X-ray machines’ intensifying screens and modern detector plates turned invisible X-rays into light using gadolinium-family phosphors.
History & name
In 1880 the Swiss chemist Jean Charles Galissard de Marignac, working in Geneva, noticed unexplained lines while examining rare-earth material from the mineral gadolinite; six years later, in 1886, the French chemist Lecoq de Boisbaudran isolated the metal itself. Both honoured the mineral in the element’s name — and gadolinite itself had been named in 1800 after Johan Gadolin, the Finnish pioneer of rare-earth chemistry. Gadolinium therefore carries a scientist’s name, twice removed.