Structure
Not a diagram of dots on rings — a Monte-Carlo sample of the actual probability density |ψ|² for each occupied subshell. Drag to rotate. Blue and violet mark opposite signs of the wavefunction, which is what makes bonding possible.
Measured values
Every bar shows where molybdenum sits among all 118 elements for that property.
Sources: IUPAC 2021 standard atomic weights · CRC Handbook of Chemistry and Physics · NIST. Values marked ~ are predicted rather than measured.
Size, to scale
Radius 139 pm — that is 0.139 nm, so about 3597 million of them side by side would span a millimetre.
Thermal range
Molybdenum is liquid over a 2016 K window, from 2896 K to 4912 K.
The story
The refractory workhorse: molybdenum keeps its strength at temperatures that soften almost everything else.
Molybdenum's discovery story begins with centuries of confusion over a mysterious black mineral that medieval miners called "molybdena." This soft, graphite-like substance was found in lead mines across Europe, but nobody understood what it actually was.
For over 1,000 years, miners and metallurgists confused molybdenite (MoS2) with graphite and galena (lead sulfide). All three minerals appear similar – dark, soft, and metallic-looking – leading to persistent misidentification. The name "molybdena" comes from the Greek word "molybdos," meaning lead, reflecting this long-standing confusion.
Swedish chemist Carl Wilhelm Scheele, already famous for discovering chlorine and oxygen, tackled the molybdena mystery in 1778. Working in his pharmacy laboratory in Köping, Sweden, Scheele suspected that molybdena was not simply a form of lead or graphite.
Scheele heated molybdena with nitric acid and observed something remarkable: instead of behaving like lead or graphite, the mineral produced a white, acidic powder. Further experiments revealed this powder had unique properties unlike any known substance.
Through meticulous chemical analysis, Scheele proved that molybdena contained a new "earth" (oxide) of an unknown metal. He named this white powder "acidum molybdenae" and correctly predicted that it contained a new element, though he couldn't isolate the pure metal with 18th-century technology.
Three years later, Scheele's colleague Peter Jacob Hjelm successfully isolated the first metallic molybdenum. Hjelm heated Scheele's acidum molybdenae with charcoal in a closed crucible, using carbon to reduce the oxide and produce small metallic granules.
Hjelm's original molybdenum sample was far from pure by modern standards, but it was definitely metallic and had properties unlike any known metal. The sample was hard, had a high melting point, and showed remarkable resistance to acids – properties that would later make molybdenum invaluable for industrial applications.
For over a century after its discovery, molybdenum remained a laboratory curiosity with no practical applications. The metal's extremely high melting point (2,623°C) made it nearly impossible to work with using 19th-century technology.
Molybdenum's industrial breakthrough came during World War I when metallurgists discovered that adding small amounts to steel dramatically improved its strength and toughness. German artillery manufacturers secretly used molybdenum steel for cannon barrels, giving them a significant military advantage.
The development of electric arc furnaces and powder metallurgy techniques in the early 20th century finally allowed production of high-purity molybdenum. By the 1930s, molybdenum had become essential for high-temperature applications, from light bulb filaments to rocket nozzles.
Scheele's careful chemical analysis and Hjelm's successful isolation represent one of chemistry's early triumphs in systematic element discovery. Their work established methods for identifying and isolating new elements that influenced chemical research for generations.
Applications
Molybdenum is a leading steel enhancer, transforming ordinary steel into high-performance alloys capable of withstanding extreme conditions. Over 80% of global molybdenum production goes into steel manufacturing, where even tiny amounts (0.1-0.5%) dramatically improve strength, hardness, and corrosion resistance.
High-speed steel tools containing 5-10% molybdenum can cut metal at speeds that would melt conventional steel tools. These "super steels" maintain their cutting edge at temperatures exceeding 600°C, revolutionizing manufacturing from automotive production to precision machining.
The global energy industry depends on molybdenum for its most challenging operations. Oil refineries use molybdenum-disulfide catalysts to remove sulfur from crude oil, producing the clean-burning fuels that power modern transportation.
Offshore drilling platforms operating in depths exceeding 3,000 meters rely on molybdenum-enhanced drill pipes and casings. These components must withstand crushing ocean pressures, corrosive saltwater, and the mechanical stress of drilling through rock formations miles below the seafloor.
Military aircraft engines contain molybdenum superalloys that operate at 85% of their melting point while spinning at 15,000 RPM. The F-35 Lightning II fighter jet uses molybdenum components in its Pratt & Whitney F135 engine, the most powerful fighter engine ever built.
NASA's Mars rovers use molybdenum heat shields and structural components to survive the -80°C Martian winters. The James Webb Space Telescope's mirrors are coated with molybdenum to reflect infrared light from the most distant galaxies in the universe.
Molybdenum plays a critical role in nuclear power generation, from reactor components to medical isotope production. The metal's high melting point (2,623°C) and low neutron absorption make it ideal for nuclear applications.
Molybdenum-99 is the parent isotope of technetium-99m, used in 85% of nuclear medicine procedures worldwide. Over 40 million medical scans annually depend on molybdenum-derived isotopes for cancer detection, heart imaging, and bone scans.
Molybdenum is an essential micronutrient for nitrogen-fixing bacteria in plant roots. Molybdenum-based fertilizers enable legume crops to convert atmospheric nitrogen into plant-usable compounds, reducing the need for synthetic nitrogen fertilizers and supporting sustainable agriculture.
Your car contains molybdenum in numerous critical components, even though you'll never see it. Engine blocks, transmission gears, and exhaust systems all benefit from molybdenum's strengthening properties. High-performance vehicles use molybdenum-enhanced brake rotors that resist warping under extreme heat.
Professional workshops and factories rely on molybdenum-enhanced tools for heavy-duty applications. Cutting tools, drill bits, and saw blades containing molybdenum stay sharp longer and work faster than conventional alternatives.
Molybdenum disulfide (MoS2) is nature's slipperiest solid, used in countless applications where traditional oils fail. This "moly" lubricant works in temperatures from -180°C to +400°C, making it essential for extreme environment applications.
Molybdenum-99 generators in hospitals worldwide produce technetium-99m for medical imaging. These "technetium cows" provide a steady supply of the most widely used medical radioisotope, enabling millions of diagnostic procedures annually.
Modern skyscrapers, bridges, and industrial facilities incorporate molybdenum steel for superior strength and durability. The Willis Tower (formerly Sears Tower) in Chicago uses molybdenum steel beams that are 25% stronger than conventional steel while weighing the same.
Where it comes from
1.2 mg/kg of Earth's crust · more abundant than 51% of elements
Molybdenum ranks 54th in abundance among Earth's elements, with an average crustal concentration of 1.2 parts per million. Despite its relative scarcity, molybdenum deposits are found on every continent, often associated with copper and tungsten ores.
China leads global production with approximately 40% of world output, followed by Chile (20%) and the United States (15%). The Climax mine in Colorado was historically the world's largest molybdenum producer, operating from 1918 to 1987.
Most commercial molybdenum comes from molybdenite (MoS2), a soft, dark gray mineral with a metallic luster. Molybdenite deposits form in high-temperature environments where molybdenum-rich fluids interact with sulfur-bearing rocks deep in Earth's crust.
The majority of molybdenum is recovered as a byproduct of copper mining from large porphyry deposits. These massive geological formations contain both copper and molybdenum minerals disseminated throughout the rock, requiring large-scale open-pit mining operations.
Molybdenum deposits form through complex hydrothermal processes that occur deep within Earth's crust. When granite magma cools slowly underground, it releases metal-rich fluids that migrate upward and deposit molybdenum minerals in fractures and contact zones.
Some molybdenum deposits form when hot granite intrusions contact limestone or other carbonate rocks. The heat and chemical interaction create unique metamorphic rocks called skarns, which can contain high concentrations of molybdenum minerals.
Earth's oceans contain approximately 10 billion tons of dissolved molybdenum, with concentrations of 10 parts per billion. While too dilute for commercial extraction, this oceanic reservoir represents the largest molybdenum inventory on our planet.
Ancient ocean sediments rich in organic matter, known as black shales, often contain elevated molybdenum concentrations. These formations, found worldwide, serve as both geological archives of ancient ocean chemistry and potential future molybdenum resources.
Molybdenum forms in the cores of massive stars through slow neutron capture processes. When these stars explode as supernovae, they scatter molybdenum across the galaxy. Our solar system's molybdenum inventory was inherited from multiple generations of stellar explosions over billions of years.
Isotopic analysis of meteorites reveals that Earth's molybdenum comes from at least two distinct stellar sources, providing clues about the early solar system's formation and the cosmic events that shaped our planet's composition.
Handling
Unlike some transition metals, molybdenum presents moderate health risks that require proper handling procedures. While not acutely toxic, chronic exposure to molybdenum compounds can cause health issues, particularly affecting the respiratory system and joints.
Dust Inhalation Risks: Prolonged exposure to molybdenum dust can cause "molybdenum pneumoconiosis," a lung condition similar to silicosis. Workers in molybdenum processing facilities must use proper respiratory protection and undergo regular health monitoring.
Combustibility: Molybdenum powder can ignite in air, especially when finely divided. Burning molybdenum produces toxic molybdenum trioxide fumes that require immediate evacuation and ventilation.
Environmental Toxicity: High molybdenum concentrations in soil can cause copper deficiency in grazing animals, leading to a condition called "molybdenosis" in cattle and sheep. Mining operations must monitor soil and water for molybdenum contamination.
Drinking Water Standards: EPA maximum contaminant level is 40 parts per billion. Natural molybdenum concentrations in groundwater near mining sites should be monitored regularly.
Quick answers
Molybdenum (symbol Mo) is element 42 on the periodic table, a transition metal in period 5, group 6. The refractory workhorse: molybdenum keeps its strength at temperatures that soften almost everything else. At room temperature it is a solid.
[Kr] 4d⁵ 5s¹, giving 5 occupied shells holding 2, 8, 18, 13, 1 electrons respectively.Molybdenum melts at 2896 K (2622.9 °C) and boils at 4912 K (4638.9 °C). That puts it among the most refractory elements — it stays solid at temperatures that vaporise most metals.
The standard atomic weight of Molybdenum is 95.95 u. That is a weighted average across its naturally occurring isotopes, which is why it is rarely a whole number.
Molybdenum has a density of 10.28 g/cm³. Water is 1.0 g/cm³, so a block of molybdenum is about 10.3× heavier.
Molybdenum has a Pauling electronegativity of 2.16. The scale runs from 0.70 (francium, the least greedy for electrons) to 3.98 (fluorine, the most). Values in this middle band tend to form covalent rather than strongly ionic bonds.
Molybdenum was discovered in 1781 by Peter Jacob Hjelm. It is named after greek molybdos, "lead".
Molybdenum makes up about 1.2 mg/kg of the Earth's crust — uncommon, but not rare.