Molybdenum (Mo)
“It refuses to melt below 2,623 °C, keeping its strength inside furnaces and X-ray machines — yet for centuries people wrote with its ore, mistaking it for lead.”
How its electrons are arranged
Computed from the aufbau principle, with known real-world exceptions applied automatically.
The notes
Characteristics
- Electron configuration [Kr] 4d⁵ 5s¹ — a textbook aufbau exception; Period 5, Group 6 transition metal with oxidation states from +2 up to +6.
- Melting point 2,623 °C, among the highest of all elements; it keeps useful strength even at red heat.
- A vital trace element for life: the nitrogenase enzyme that fixes N₂ for legumes and the xanthine oxidase in our own bodies both contain molybdenum.
- Forms extremely hard carbides, so small additions toughen steel; the metal itself resists corrosion and attacks by many acids.
A silvery-grey metal with a rather dark, rough cast surface; hard, but noticeably more ductile than its neighbour tungsten. Only a handful of elements melt at a higher temperature than its 2,623 °C.
Where you meet it
✦ Uses
- Molybdenum in stainless steel — the 316 grade with about 2 % Mo resists rust, so kitchen sinks, quality cutlery and chemical pipes are made from it.
- Molybdenum disulfide (MoS₂) “moly grease” — a dry lubricant for car CV joints, locks and heavy machinery where oil would wash away.
- High-speed tool steels and armour steels; also the rotating X-ray tube targets that let hospitals take sharp CT images.
- Catalysts that strip sulfur out of petroleum so that vehicle fuel and diesel meet clean-air rules.
◍ Everyday examples
- The shiny stainless-steel spoon and kitchen sink at home — if the steel is grade 316, about two parts in a hundred are molybdenum.
- The grease a mechanic packs into a truck’s wheel joints at the roadside garage is often black with MoS₂.
- The root nodules of lentil and gram plants in a field house molybdenum-dependent nitrogen-fixing bacteria — the element quietly feeds the dal on your plate.
History & name
The soft black mineral molybdenite (MoS₂) looks exactly like graphite or lead ore, and for centuries miners called it molybdena and even wrote with it. In 1778 the Swedish chemist Carl Wilhelm Scheele showed that this “lead” contained no lead at all: treating it with nitric acid produced a new acid, from which he inferred a new element. In 1781 his fellow Swede Peter Jacob Hjelm reduced the acid with carbon in a furnace and obtained the grey metal molybdenum. The name comes from the Greek molybdos, “lead” — a permanent memory of the old confusion.