Transition Metal Characteristics
In the Periodic Table, d-block (as well as f-block) elements (Ti, Fe, Cr, Ni, Cu, Mo) are called transition metals because they are located between the s- and p-block elements. Their properties represent the transition between the highly reactive metallic elements of the s-block, which also give ionic compounds, and the elements of the p-block, which are mainly covalent.
About 56 transition elements out of a total of 104 elements are known so far in the Periodic Table. Because of their similar electronic configurations, they closely resemble one another in their physical and chemical properties.
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Basic Properties
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They are hard, strong, high-melting and high-boiling metals, which makes them good conductors of heat and electricity. They can easily create alloys with one another, and also with other groups of metals. Many of them are electropositive enough to dissolve in mineral acids, whereas a few of them are not attacked by simple acids because of their low electrode potentials. With a few exceptions, they show variable valency or oxidation states and have the ability to form numerous complexes.
Density
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The atomic volumes of the transition metals are relatively small. Hence the densities of the transition metals are high.
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Reactivity of Metals
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The metals show a tendency to behave as noble or un-reactive metals. This is favored by high heats of sublimation, high ionization energies and low heats of salvation.
Ionization Energies
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The ionization energies of transition metals are intermediate between those for the s- and p-block elements. This indicates that the transition elements are less electropositive and might form either ionic or covalent bonds depending on conditions. In general, the lower valent states are ionic and the higher valent states are covalent.
Color
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Transition metals are generally colorless, while the ionic and covalent compounds of transition metals are colored. Color is associated with the ability to promote an electron from one energy level to another by absorption of light.
Magnetic Properties
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The transition metals and their compounds show magnetic properties. Many compounds of the transition metals are paramagnetic because of unpaired electron spins in the atom.
Catalytic Properties
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Many transition metals and their compounds possess catalytic properties. Some important examples are ferrous sulphate and hydrogen peroxide (used as Fenton's reagent for oxidizing alcohols to aldehydes); Fe/Mo (manufacture of ammonia to nitric oxide); and vanadium oxide (oxidation of sulfur dioxide to sulfur trioxide).
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References
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