Palladium

Palladium's ground state configuration is [Kr] 4d¹⁰ with nothing in 5s at all — the only element in the table whose outermost s subshell is empty in the neutral atom. Wollaston discovered it in 1802 and, in a strange episode, sold it anonymously through a London shop as a new silver, provoking a public accusation of fraud from the chemist Richard Chenevix before Wollaston revealed himself. The metal absorbs up to about 900 times its own volume of hydrogen, which is why Fleischmann and Pons used palladium electrodes in their 1989 cold fusion claim, and why it is used in hydrogen purification membranes. Its lasting importance is catalytic: palladium-catalysed cross-coupling reactions, recognised with the 2010 Nobel Prize to Heck, Negishi and Suzuki, are the standard way to build carbon-carbon bonds in pharmaceutical manufacture.