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ChemWiki: The Dynamic Chemistry E-textbook > Inorganic Chemistry > Descriptive Chemistry > d-Block Elements > Group 7: Transition Metals

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Group 7: Transition Metals

Manganese (Mn)

The name of the 25th element comes from the Latin magnes, meaning magnet. It was discovered in 1774 by Scheele and isolated later that year by Johan Gahn.

In pure form Manganese is a hard, brittle, gray-white metal. It is best known as an alloying agent in steel. It enhances the ability to hot-work steel and increases resistance to impact. In biological systems manganese is a crucial component of vitamin \(B_1\).

The pure metal is produced from its most common compound (MnO2---10th most abundant compound in the earth's crust). It can be reduced chemically or refined electrolytically. The element has at least 5 stable oxidation states with distinctive colors (as is typical of transition metals). It is commonly encountered in the laboratory as the compound \(KMnO_4\) which is a strong oxidizing agent. \(MnO_2\) catalyzes the decomposition of \(H_2O_2\) and is sometimes used for the small scale production of oxygen gas in the lab.

Technetium (Tc)

Technetium has the distinction of being the first synthetically produced element. It was the last of the six elements predicted by Mendeleev to be discovered (in 1937 by Segrè and Perrier). Trace amounts were found in a sample of molybdenum that had been bombarded with deuterons in a cyclotron.

All known isotopes of Tc are radioactive and none appears to occur naturally on earth. However, it is produced commercially in kg quantities because very tiny amounts (55 parts per million) can transform iron into a corrosion resistant alloy. All applications of the metal involve closed systems, however, because of the radioactivity.

Pure Tc is a silvery-gray metal similar in appearance to platinum but it is normally produced in powdered form. Chemically it resembles a cross between Mn and Re. Although of little interest, compounds have been prepared in which Tc exhibits oxidation states of +4, +6 and +7.

Rhenium (Re)

A dense, silvery white metal, Rhenium takes its name from the Latin, Rhenus, for the Rhine river. It was discovered in 1925 by Ida and Walter Noddack along with Otto Berg. It is nearly twice as dense as lead (21 g/cm3) and extremely rare (1 pound of rhenium per 1000 million pounds of earth!!!). Nonetheless, the total annual U.S. production of Re is almost half a ton. It is used as a trace alloying element for metal components that are subject to constant friction.

Rhenium was another of the "missing" elements proposed by Mendeleev. The first sample was concentrated 100,000 fold from a gadolinium ore sample. Just enough was obtained for a spectroscopic study in which previously unseen lines were observed. The metal is acid resistant and has one of the highest melting points. But its scarcity (and therefore expense) makes practical use limited.

Bohrium (Bh)

Element 107 (Uns) was first reported by Soviet scientists in 1976. This claim has since been substantiated by German researchers but no name was suggested and so it has been known by its numerical moniker, unnilseptium (107).

Recently, however, a committee of the IUPAC suggested the name Bohrium (after Niels Bohr). This name was finally approved in August 1997. There are no practical uses for Bohrium. All known isotopes have extremely short half-lives.

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