Molybdenum (Mo)

Molybdenum (symbol Mo) is the chemical element with atomic number 42: a transition metal, solid at 0 °C, with an atomic mass of 95.95 u. Discovered in 1778 (Carl Wilhelm Scheele).

Molybdenum is a metal with a very high melting point (2,623 °C) that strengthens steels and makes them resistant to heat and corrosion. It is also a trace element essential to almost all living things. Its Greek name means “lead,” because its ore was once confused with lead and graphite.

Key facts

Atomic number: 42
Symbol: Mo
French name: Molybdène
Atomic mass: 95.95 u
Molar mass: 95.95 g/mol
Family: Transition metals
Position: period 5, group 6, d-block
State at 0 °C: Solid
Melting point: 2,622.9 °C
Boiling point: 4,638.9 °C
Density: 10.28 g/cm³
Electronegativity (Pauling): 2.16
First ionization energy: 684 kJ/mol
Atomic radius: 145 pm
Electron configuration: [Kr] 4d⁵ 5s¹
Abundance in Earth's crust: 1.2 ppm (58th most abundant element)
Indicative price: 40 $/kg (order of magnitude)
Radioactive: no
Discovery: 1778, Carl Wilhelm Scheele

Origin of the name

From the Greek molybdos, lead.

What does molybdenum look like?

A hard, highly refractory, silvery-gray metal. Its main ore, molybdenite, looks uncannily like graphite: gray, greasy to the touch, and it leaves a mark on paper.

Where is molybdenum found?

About 1 to 1.5 ppm of Earth's crust. It is found mainly in large “porphyry” copper-molybdenum deposits, notably in the Andes and the Rockies.

Natural sources

Molybdenite
Wulfenite
Powellite

How is molybdenum produced?

Molybdenite (MoS₂) is mined, often as a by-product of copper, then roasted into oxide, which is turned into ferromolybdenum or reduced to metal with hydrogen. World output is about 250,000 tonnes a year.

Top producers

China
Peru
Chile
United States

What is molybdenum used for?

Alloy and stainless steels (such as 316 stainless, which resists salt).
Catalysts that remove sulfur from fuels.
Molybdenum disulfide solid lubricant.
Producing molybdenum-99, the source of medical technetium.
Electrodes and parts for high-temperature furnaces.

In everyday life

Stainless steel for boats and kitchens
“Moly” grease for mechanics
Low-sulfur diesel at the pump

Role in living things

Essential: it sits at the heart of enzymes such as xanthine oxidase and sulfite oxidase, which break down waste and toxins. In bacteria, molybdenum nitrogenase turns nitrogen from the air into natural fertilizer, on which much of life on Earth depends. Legumes, grains and organ meats supply plenty.

Hazards of molybdenum

Low toxicity for humans. In ruminants, an excess interferes with copper absorption and can make them ill.

Cosmic origin

Dying stars: Made slowly in red giants (stars like the Sun at the end of their lives).
Supernovae: Forged in the cores of massive stars, then scattered when they explode.

History of molybdenum

In antiquity, lead, graphite and molybdenite were all lumped under the same Greek name, molybdos. In 1778, Swede Carl Wilhelm Scheele showed that molybdenite contains an unknown element, which his compatriot Peter Jacob Hjelm isolated in 1781.

Did you know?

Without the molybdenum in nitrogen-fixing bacteria, most plants would go short of natural fertilizer.
The Climax mine in Colorado long supplied most of the world's molybdenum.
Like graphene, molybdenum disulfide can be thinned down to a single layer, studied for the electronics of the future.

Isotopes of molybdenum

Six stable isotopes, plus barely radioactive molybdenum-100. Molybdenum-99, made in reactors, is the source of the technetium-99m used in hospitals worldwide.

molybdenum-92: 14.53% of natural molybdenum, stable
molybdenum-93: radioactive, half-life 4,000 years
molybdenum-94: 9.15% of natural molybdenum, stable
molybdenum-95: 15.84% of natural molybdenum, stable
molybdenum-96: 16.67% of natural molybdenum, stable
molybdenum-97: 9.6% of natural molybdenum, stable
molybdenum-98: 24.39% of natural molybdenum, stable
molybdenum-99: radioactive, half-life 2.75 days. Shipped to hospitals in a “generator” that churns out technetium-99m.
molybdenum-100: 9.82% of natural molybdenum, radioactive, half-life 7.07 × 10¹⁸ years. Studied for double beta decay; can also yield technetium-99m in an accelerator.

Related elements

Same family (transition metals): Scandium (Sc), Titanium (Ti), Vanadium (V), Chromium (Cr), Manganese (Mn), Iron (Fe), Cobalt (Co), Nickel (Ni), Copper (Cu), Zinc (Zn), Yttrium (Y), Zirconium (Zr), Niobium (Nb), Technetium (Tc), Ruthenium (Ru), Rhodium (Rh), Palladium (Pd), Silver (Ag), Cadmium (Cd), Hafnium (Hf), Tantalum (Ta), Tungsten (W), Rhenium (Re), Osmium (Os), Iridium (Ir), Platinum (Pt), Gold (Au), Mercury (Hg), Rutherfordium (Rf), Dubnium (Db), Seaborgium (Sg), Bohrium (Bh), Hassium (Hs).

Same column (group 6): Chromium (Cr), Tungsten (W), Seaborgium (Sg).