Lanthanum (La)
“It hid inside “cerium” for years — now lanthanum glass sharpens camera lenses and its alloy stores hydrogen inside rechargeable batteries.”
How its electrons are arranged
Computed from the aufbau principle, with known real-world exceptions applied automatically.
Characteristics
- Electron configuration [Xe] 5d¹ 6s² — the 4f sub-shell is still completely empty; a textbook exception, since plain aufbau order would wrongly predict 4f¹ 6s².
- The metal tarnishes within minutes, burns readily once lit, and reacts with hot water to release hydrogen and form lanthanum hydroxide.
- Its chemistry is almost entirely the colourless La³⁺ ion; having no 4f electrons at all, its compounds lack the colourful f–f transitions of its lanthanide cousins.
- Surprisingly common for a “rare earth” — about three times as abundant as lead in the Earth’s crust, yet scattered so thinly that extraction was long a struggle.
A soft, silvery-white metal, easy to cut and dent, that keeps its polish only briefly — a freshly cut face clouds over within minutes as air attacks it. It is the first of the fifteen lanthanides and behaves like a typical reactive rare-earth metal, stored under oil in the laboratory.
Where you meet it
✦ Uses
- Lanthanum oxide in extra-clear, high-refractive-index camera and telescope lens glass — the glass that lets a smartphone or DSLR capture sharp, undistorted pictures.
- LaNi₅ hydrogen-storage alloy in the negative electrode of NiMH rechargeable batteries — the AAs in cameras and the big packs in hybrid cars.
- Lanthanum carbonate (Fosrenol) chewed with meals by kidney-dialysis patients, binding the excess phosphate their failed kidneys can no longer remove.
- Petroleum refining: lanthanum exchanged into the zeolite catalysts of FCC units that crack heavy crude into petrol, diesel and LPG.
◍ Everyday examples
- A NiMH rechargeable AA battery running a camera flash or a toy at home carries lanthanum-rich alloy in its negative electrode.
- The crisp, colour-true image from a good pair of binoculars or a DSLR lens usually passes through glass containing a few percent of lanthanum oxide.
- The petrol and diesel sold at Bangladeshi filling stations were cracked in FCC units whose lanthanum-bearing zeolite catalysts did the chemistry.
History & name
By 1838 the Swedish chemist Carl Gustaf Mosander had begun to suspect that the recently discovered element cerium was not pure. Heating cerium nitrate and picking apart the residue, he extracted a new oxide in 1839 — a whole new element had been hiding inside cerium all along. He named it lanthanum, from the Greek lanthanein, “to lie hidden”. The trick soon became a habit: hidden impurities kept surrendering more new elements, and lanthanum opened the door to the entire lanthanide family.