Average mass of an atom in unified atomic mass units (1 u is 1/12 of the mass of a carbon-12 atom). Accounts for the natural mix of the element’s isotopes.
Number of the vertical column, 1 to 18 in IUPAC numbering. Elements in a group share the same outer-shell layout, so their properties are alike.
Number of the horizontal row. Usually equal to the number of electron shells in the atom; palladium is the exception, with four shells in period 5.
The subshell (s, p, d or f) that receives the last electrons in the usual filling order; it divides the table into four blocks. Real atoms sometimes differ: lanthanum starts the f-block but has no f electrons.
[Kr] 5s¹ 4d⁵
How electrons are arranged in subshells. The bracket stands for the previous noble gas; the superscript is the number of electrons in a subshell.
2, 8, 18, 13, 1
Number of electrons in each shell, from the nucleus outwards.
2,623 °C (2,896 K)
Temperature at which the solid turns liquid at standard pressure. Helium, carbon and arsenic do not melt at normal pressure: helium needs about 25 atm, carbon and arsenic turn straight into vapour.
4,639 °C (4,912 K)
Temperature at which the liquid boils at standard pressure. For carbon and arsenic, the temperature at which the solid turns straight into vapour (sublimation).
10.2 g/cm³
Mass of one cubic centimetre of the substance. For gases, at 0 °C and standard pressure.
2.16 Pauling
How strongly an atom pulls electrons towards itself in a chemical bond. On the Pauling scale it runs from 0.79 for caesium to 3.98 for fluorine.
7.092 eV
Energy needed to remove the most loosely bound electron from an atom. The lower it is, the more easily the element gives up an electron, which is typical of metals.
0.747 eV
Energy released when a neutral atom gains an electron. Highest for the halogens. Noble gases, nitrogen and some metals form no stable negative ion.
154 pm
Half the length of a single covalent bond between two atoms of the element. It shows the size of an atom inside a molecule or crystal: 76 pm for carbon, 132 pm for iron.
+6, +4
Charges the atom would have in its compounds if all its bonds were ionic; the main ones are listed.
Molybdenum (Mo) is a chemical element with atomic number 42. It sits in group 6 and period 5 of the periodic table, in the d-block. It is a transition metal. At room temperature it is a solid. Its standard atomic weight is 95.95.
Origin of the name
The name comes from the Greek molybdos, ‘lead’. The soft, black mineral molybdenite leaves a grey mark like a pencil, and for centuries it was confused with graphite and with lead ore. In 1778 Carl Wilhelm Scheele showed that it was neither and contained a new element; a few years later Peter Jacob Hjelm obtained the metal.
Where is molybdenum found?
Molybdenum is never found as a metal in nature. It is mined mostly from molybdenite, a molybdenum sulfide, and also comes as a by-product of copper mining.
What is molybdenum used for?
About four-fifths of all molybdenum goes into steel: it makes steel very strong and keeps it strong at high temperatures, in tools, engines and aircraft parts. Molybdenum disulfide is a lubricant that works where oils would burn, and molybdenum catalysts are used in oil refineries.
Interesting facts
Radioactive molybdenum-99 decays into technetium-99m, which is widely used in medical imaging.
Bacteria that take nitrogen from the air and turn it into food for plants do it with enzymes containing molybdenum.