Molybdenum

The name comes from molybdos, the Greek for lead, because molybdenite is soft, grey and marks paper much like galena and graphite, and nobody could tell the three apart until Scheele separated them in 1778. Molybdenum raises steel's strength and creep resistance at high temperature, which is why Krupp used it in the barrels and armour of the First World War and why it is standard in 316 stainless, tool steels and pressure-vessel alloys. Molybdenum disulfide, structurally a cousin of graphite, is the dry lubricant that works in vacuum and under extreme pressure. Biologically it is the only second-row transition metal life uses widely: the iron-molybdenum cofactor of nitrogenase is what lets bacteria break the N≡N bond at ambient temperature, a reaction industry needs 400 °C and 200 atmospheres to force. Its ground state is 4d⁵ 5s¹.