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Concept
Groupe 5 du tableau périodique
Résumé
Group 5 is a group of elements in the periodic table. Group 5 contains vanadium (V), niobium (Nb), tantalum (Ta) and dubnium (Db). This group lies in the d-block of the periodic table. This group is sometimes called the vanadium group or vanadium family after its lightest member; however, the group itself has not acquired a trivial name because it belongs to the broader grouping of the transition metals.
As is typical for early transition metals, niobium and tantalum have only the group oxidation state of +5 as a major one, and are quite electropositive (it is easy to donate electrons) and have a less rich coordination chemistry (the chemistry of metallic ions bound with molecules). Due to the effects of the lanthanide contraction, the decrease in ionic radii in the lanthanides, they are very similar in properties. Vanadium is somewhat distinct due to its smaller size: it has well-defined +2, +3 and +4 states as well (although +5 is more stable).
The lighter three Group 5 elements occur naturally and share similar properties; all three are hard refractory metals under standard conditions. The fourth element, dubnium, has been synthesized in laboratories, but it has not been found occurring in nature, with half-life of the most stable isotope, dubnium-268, being only 16 hours, and other isotopes even more radioactive.
"Group 5" is the new IUPAC name for this group; the old style name was "group VB" in the old US system (CAS) or "group VA" in the European system (old IUPAC). Group 5 must not be confused with the group with the old-style group crossed names of either VA (US system, CAS) or VB (European system, old IUPAC). That group is now called the pnictogens or group 15.
Vanadium was discovered in 1801 by the Spanish mineralogist Andrés Manuel del Río. Del Río extracted the element from a sample of Mexican "brown lead" ore, later named vanadinite. He found that its salts exhibit a wide variety of colors, and as a result he named the element panchromium (Greek: παγχρώμιο "all colors").
Source officielle
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