Chemical Properties
closed-packed hexagonal, a=0.2741 nm, c=0.4399nm; enthalpy of sublimation 650 kJ/mol; enthalpy of vaporization ~577 kJ/mol; enthalpy of fusion 33.29 kJ/mol; slowly tarnishes in moist air; when obtained from H2 reduction of ammonium pertechnate, has silvery gray color, and a spongy mass; resembles rhenium in chemical behavior; Debye constant 455K; used as a metallurgical tracer, in nuclear medicine, and to protect against corrosion [HAW93] [MER06] [RAR83] [CRC10]
Uses
Minute quantities of TcO4- ion exert remarkable inhibition of the corrosion of soft iron in neutral aqueous solution: Cartledge, J. Am. Chem. Soc. 77, 2658 (1955).
Physical properties
As the central member of the triad of metals in group 7, technetium (period 5) has similarphysical and chemical properties as its partners manganese (period 4) above it and rhenium(period 6) below it. The sizes of their atomic radii do not vary greatly: Mn = 127, Tc = 136,and Re = 137. Neither does their level of electronegativity vary significantly: Mn = 1.5, Tc =1.9, and Re = 1.9.
Technetium metal is grayish-silver and looks much like platinum. As with most transitionelements, technetium in pure form is a noncorrosive metal. It requires only 55 ppm of technetiumadded to iron to transform the iron into a noncorroding alloy. Because of technetium’sradioactivity, its use as an alloy metal for iron is limited so as to not expose humans to unnecessaryradiation.
Technetium’s melting point is 2,172°C, its boiling point is 4,877°C, and its density is11.50 g/cm3 .
Isotopes
There are 47 isotopes. None are stable and all are radioactive. Most are producedartificially in cyclotrons (particle accelerators) and nuclear reactors. The atomicmass of its isotopes ranges from Tc-85 to Tc-118. Most of technetium’s radioactiveisotopes have very short half-lives. The two natural radioisotopes with the longest halflives—Tc-98 = 4.2×10+6 years and Tc-99 = 2.111×10+5 years—are used to establishtechnetium’s atomic weight.
Origin of Name
Technetium’s name was derived from the Greek word technetos,
meaning “artificial.”
Occurrence
Technetium is the 76th most abundant element, but it is so rare that it is not found as astable element on Earth. All of it is artificially produced. Even though natural technetium isso scarce that it is considered not to exist on Earth, it has been identified in the light spectrumfrom stars. Using a spectroscope that produces unique lines for each element, scientists areable to view several types of stars. The resulting spectrographs indicate that technetium existsin the stars and thus the universe, but not on Earth as a stable element.
It was the first new element to be produced artificially from another element experimentallyin a laboratory. Today, all technetium is produced mostly in the nuclear reactors of electricalgeneration power plants. Molybdenum-98 is bombarded with neutrons, which then becomesmolybdenum-99 when it captures a neutron. Since Mo-99 has a short half-life of about 66hours, it decays into Tc-99 by beta decay.
Characteristics
Technetium was the first element, not found on Earth, to be artificially produced by bombardingmolybdenum with deuterons.
The major characteristic of technetium is that it is the only element within the 29 transitionmetal-to-nonmetal elements that is artificially produced as a uranium-fission product innuclear power plants. It is also the lightest (in atomic weight) of all elements with no stableisotopes. Since all of technetium’s isotopes emit harmful radiation, they are stored for sometime before being processed by solvent extraction and ion-exchange techniques. The two longlivedradioactive isotopes, Tc-98 and Tc-99, are relatively safe to handle in a well-equippedlaboratory.
Since all of technetium’s isotopes are produced artificially, the element’s atomic weight(atomic mass units) is determined by which isotopes are selected for the calculation.
Definition
A transition metal that does not occur naturally on Earth. It is produced artificially by bombarding molybdenum with neutrons and also during the fission of uranium. It is radioactive. Symbol: Tc; m.p. 2172°C; b.p. 4877°C; r.d. 11.5 (est.); p.n. 43; r.a.m. 98.9063 (99Tc); most stable isotope 98Tc (half-life 4.2 × 106 years).
Definition
technetium: Symbol Tc. A radioactivemetallic transition element;a.n. 43; m.p. 2172°C; b.p. 4877°C. Theelement can be detected in certainstars and is present in the fissionproducts of uranium. It was firstmade by Carlo Perrier and EmilioSegré (1905–89) by bombardingmolybdenum with deuterons to givetechnetium–97. The most stable isotopeis technetium–99 (half-life 2.6 ×106 years); this is used to some extentin labelling for medical diagnosis.There are sixteen known isotopes.Chemically, the metal has propertiesintermediate between manganeseand rhenium.
Preparation
Technetium isotopes are prepared by bombardment of molybdenum with protons and neutrons. A few nuclear reactions are shown for the three longlived isotopes:
Technetium-99 also is a fission product of uranium-235.
Pure technetium metal may be prepared by reducing ammonium pertechnate, NH4TcO4, with hydrogen at high temperatures. Hydrogen reduction at about 200°C first forms the oxide, TcO
2, which is reduced to Tc metal at 600 to 800°C.
Hazard
The hazards of technetium are the same as for all radioactive elements. Excessive exposureto radiation can cause many kinds of tissue damage—from sunburn to radiation poisoningto death.
