Palladium (Pd)
“Chemistry’s aufbau rebel — both 5s electrons have fled into 4d, leaving [Kr] 4d¹⁰ — an asteroid-named metal that soaks up 900 times its own volume of hydrogen.”
How its electrons are arranged
Computed from the aufbau principle, with known real-world exceptions applied automatically.
The notes
Characteristics
- Electron configuration [Kr] 4d¹⁰ — the famous aufbau exception: both 5s electrons have slipped into 4d, leaving 5s empty; the filled d subshell buys extra stability where the rulebook predicts [Kr] 4d⁸ 5s².
- Soaks up hydrogen like a sponge — up to about 900 times its own volume at room temperature — forming a hydride in which hydrogen atoms sit inside the metal lattice.
- The lightweight of its noble family: lowest density and lowest melting point (about 1,555 °C) of the six platinum-group metals, while air, moisture and single acids leave it unharmed.
- A gentle giant of catalysis — hydrogen molecules landing on palladium split into atoms at the surface, the first step of countless hydrogenation reactions, including the Lindlar catalyst that turns alkynes into cis-alkenes.
A light, bright silvery-white platinum-family metal that never tarnishes in air. It is the runt of its noble litter — lowest density, lowest melting point — yet so ductile that it can be beaten into leaf thinner than a soap bubble’s film.
Where you meet it
✦ Uses
- Catalytic converters of petrol cars — palladium oxidises carbon monoxide and unburnt hydrocarbons, making motoring the metal’s biggest single customer.
- Dental crowns and bridges — strong, light palladium-silver “white alloys” have filled millions of mouths worldwide.
- Multilayer ceramic capacitors in electronics — a single smartphone carries hundreds, many with palladium or silver-palladium electrodes.
- Hydrogen purification membranes — hydrogen atoms diffuse through hot palladium foil but no other gas can pass, yielding ultra-pure gas; jewellers also sell it as a featherweight platinum alternative.
◍ Everyday examples
- Dental clinics in any Bangladeshi town — white-gold dental castings are very often palladium alloys.
- The smartphone in a student’s pocket hides hundreds of palladium-bearing capacitors on its circuit board.
History & name
In 1802–03 William Hyde Wollaston isolated palladium from crude South American platinum — and then did something bizarre: he announced the new metal anonymously on a printed handbill, selling it through a London shop at thirty shillings an ounce. The Irish chemist Richard Chenevix publicly denounced it as a fraudulent platinum-mercury alloy, igniting chemistry’s famous “Palladium affair”. Wollaston quietly offered a reward to anyone who could make that alloy himself — nobody could — and finally unmasked himself in 1805. The name honoured the asteroid Pallas, discovered barely a year earlier and itself named for the Greek goddess of wisdom.