|
General |
Name, Symbol, Number | molybdenum, Mo, 42 |
Chemical series | transition metal |
Group, Period, Block | 6 (VIB), 5 , d |
Density, Hardness | 10280 kg/m3, 5.5 |
Appearance | grey metallic |
Atomic Properties |
Atomic weight | 95.94 amu |
Atomic radius | 145 pm |
Covalent radius | 145 pm |
van der Waals radius | not known pm |
Electron configuration | [Kr]4d55s1 |
e- 's per energy level | 2, 8, 18, 13, 1 |
Oxidation states (Oxide) | 2,3,4,5,6 (strong acid) |
Crystal structure | body centered cubic |
Physical Properties |
State of matter | solid (__) |
Melting point | 2896 K (4753 °F) |
Boiling point | 4912 K (8382 °F) |
Molar volume | 9.38 ×10-3 m3/mol |
Heat of vaporization | 598 kJ/mol |
Heat of fusion | 32 kJ/mol |
Vapor pressure | 3.47 Pa at 3000 K |
Speed of sound | __ m/s at __ K |
Miscellaneous |
Electronegativity | 2.16 (Pauling scale) |
Specific heat capacity | 250 J/(kg*K) |
Electrical conductivity | 18.7 106/m ohm |
Thermal conductivity | 138 W/(m*K) |
1st ionization potential | 684.3 kJ/mol |
2nd ionization potential | 1560 kJ/mol |
3rd ionization potential | 2618 kJ/mol |
4th ionization potential | 4480 kJ/mol |
Most Stable Isotopes |
iso | NA | half-life | DM | DE MeV | DP |
93Mo | {syn.} | 4000 y | ε | 0.405 | 93Nb |
99Mo | {syn.} | 65.94 h | β | 1.357 | 99Tc |
100Mo | {syn.} | 1E19 y | β | 3.034 | 100Ru |
92Mo | 14.84% | Mo is stable with 50 neutrons |
94Mo | 9.25% | Mo is stable with 52 neutrons |
95Mo | 15.92% | Mo is stable with 53 neutrons |
96Mo | 16.68% | Mo is stable with 54 neutrons |
97Mo | 9.55% | Mo is stable with 55 neutrons |
98Mo | 24.13% | Mo is stable with 56 neutrons |
|
SI units & STP are used except where noted. |
Molybdenum is a
chemical element in the
periodic table that has the symbol Mo and
atomic number 42.
Molybdenum is a
transition metal. The pure metal is silvery white in color and very hard, and has one of the highest melting points of all pure elements. In small quantities, molybdenum is effective at hardening
steel. Molybdenum is important in plant nutrition, and is found in certain
enzymes, including
xanthine oxidase.
Over 2/3 of all molybdenum is used in
alloys. Molybdenum use soared during
World War I, when demand for
tungsten made tungsten scarce, and high strength
steels were at a premium. Molybdenum is used to this day in high strength alloys, and high temperature steels. Special molybdenum containing alloys, such as the
Hastelloys[?] ®, are notably heat resistant and
corrosion resistant. Molybdenum is used in
aircraft and
missile parts, and in filaments. Molybdenum finds use as a
catalyst in the
petroleum industry, especially in catalysts for removing organic
sulfurs from petroleum products. Mo-99 is used in the nuclear isotope industry. Molybdenum oranges are pigments, ranging from
red-
yellow to a bright red
orange, used in
paints,
inks,
plastics, and
rubber compounds. Molybdenum disulphide is a good
lubricant, especially at high temperatures. Molybdenum is also used in some electronic applications, as the conductive metal layers in
thin-film transistors (TFTs).
Molybdenum (from the
Greek molybdos meaning "lead-like") is not found free in nature, and the compounds that can be found were, until the late
18th century, confused with compounds of other elements, such as
carbon or
lead. In
1778 Carl Wilhelm Scheele was able to determine that molybdenum was separate from
graphite and lead, and was able to isolate the
oxide of the metal from
molybdenite[?]. In
1782 Hjelm[?] was able to isolate an impure extract of the metal by reducing the oxide with carbon. Molybdenum was little used and remained in the laboratory until the late
19th century. Then a French company,
Schneider and Co[?], tried molybdenum as an alloying agent in armor plate and noted its useful properties.
Though molybdenum is found in such
minerals as
wulfenite[?] (Mo
O4Pb) or powellite (
CaMnO
4), the main commercial source of molybdenum is molybdenite (Mo
S2). Molybdenum is mined directly, and is also recovered as a by-product of
copper mining. Molybdenum is present in
ores from 0.01% to about 0.5%. About half of the world's molybdenum is mined in the
United States.
There is a trace requirement for molybdenum in
plants, and
soils can be barren due to molybdenum deficiencies. Plants and animals generally have molybdenum, present in amounts of a few parts per million. In plants, molybdenum is involved in the pathways of
nitrogen fixation and
nitrate reduction, and in
animals, molybdenum is involved in the pathways of
purine degredation and formation of
uric acid. In some animals, adding a small amount of dietary molybdenum enhances growth.
Molybdenum has six
stable isotopes and almost two dozen
radioisotopes, the vast majority of which have
half lives measured in seconds. Mo-99 is used in
sorpation generators[?] that are used to create Tc-99 for the nuclear
isotope industry. The market for Mo-99 products is estimated to be on the order of $100 million
US dollars a year.
Molybdenum dusts and molybdenum compounds, such as molybdenum trioxide and water soluble molybdates, may have slight
toxicities if inhaled or ingested orally. Laboratory tests suggest, compared to many
heavy metals, that molybdenum is of relatively low toxicity. Acute toxicity in
humans is an unlikely because the dose required would be exceptionally large. There is the potential for molybdenum exposure in
mining and refining operations, as well as the chemical industry, but to date, no instance of harm from this exposure has been reported. Though water-soluble molybdenum compounds can have a slight toxicity, those that are insoluble, such as the lubricant molybdenum disulfide, are considered to be nontoxic. However, environmental chains of events can end in serious molybdenum-related health consequences. In 1996 in Sweden an increase in acid rain near
Uppsala caused a depletion in the natural foods of moose in nearby rural areas; this caused the moose to venture into the fields of oat farmers who had been heavily liming their soil to compensate for the effect of the acid; the lime caused changes to the levels of
cadmium and other trace metals in the soil, causing the oat crops to uptake trace molybdenum in large quantities; ingestion of the oats by hundreds of moose brought on a severe disturbance in the ratio of molybdenum to copper in their livers, which caused emaciation, hair discoloration, ulcers, diarrhea, convulsions, blindness, osteoporosis and finally heart failure.
OSHA regulation specify that maximum exposure in a 8 hour day, 40 hour week to molybdenum be 15 milligrams per cubic meter. NIOSH recommended exposure limit is 5000 mg per cubic meter.