↓ Period 4 5 6 7 Legend primordial element synthetic element
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.
History
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
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"). Later, Del Río renamed the element erythronium (Greek: ερυθρός "red") because most of the salts turned red upon heating. In 1805, French chemist Hippolyte Victor Collet-Descotils, backed by del Río's friend Baron Alexander von Humboldt, incorrectly declared that del Río's new element was an impure sample of chromium. Del Río accepted Collet-Descotils' statement and retracted his claim.
In 1831 Swedish chemist Nils Gabriel Sefström rediscovered the element in a new oxide he found while working with iron ores. Later that year, Friedrich Wöhler confirmed del Río's earlier work. Sefström chose a name beginning with V, which had not yet been assigned to any element. He called the element vanadium after Old Norse Vanadís (another name for the Norse Vanir goddess Freyja, whose attributes include beauty and fertility), because of the many beautifully colored chemical compounds it produces. In 1831, the geologist George William Featherstonhaugh suggested that vanadium should be renamed rionium after del Río, but this suggestion was not followed.
Niobium and tantalum
Niobium was identified by English chemist Charles Hatchett in 1801. He found a new element in a mineral sample that had been sent to England from Connecticut, United States in 1734 by John Winthrop F.R.S. (grandson of John Winthrop the Younger) and named the mineral columbite and the new element columbium after Columbia, the poetic name for the United States. However, after the 15th Conference of the Union of Chemistry in Amsterdam in 1949, the name niobium was chosen for element 41. The columbium discovered by Hatchett was probably a mixture of the new element with tantalum, which was first discovered in 1802 by Anders Gustav Ekeberg.
Subsequently, there was considerable confusion over the difference between niobium (columbium) and the closely related tantalum. In 1809, English chemist William Hyde Wollaston compared the oxides derived from both niobium - columbite, with a density 5.918 g/cm, and tantalum - tantalite, with a density over 8 g/cm, and concluded that the two oxides, despite the significant difference in density, were identical; thus he kept the name tantalum. This conclusion was disputed in 1846 by German chemist Heinrich Rose, who argued that there were two different elements in the tantalite sample, and named them after children of Tantalus: niobium (from Niobe) and pelopium (from Pelops). This confusion arose from the minimal observed differences between tantalum and niobium. The claimed new elements pelopium, ilmenium, and dianium were in fact identical to niobium or mixtures of niobium and tantalum. Pure tantalum was not produced until 1903.
Dubnium
The last element of the group, dubnium, does not occur naturally and so must be synthesized in a laboratory. The first reported detection was by a team at the Joint Institute for Nuclear Research (JINR), which in 1968 had produced the new element by bombarding an americium-243 target with a beam of neon-22 ions, and reported 9.4 MeV (with a half-life of 0.1–3 seconds) and 9.7 MeV (t1/2 > 0.05 s) alpha activities followed by alpha activities similar to those of either 256103 or 257103. Based on prior theoretical predictions, the two activity lines were assigned to 261105 and 260105, respectively.
After observing the alpha decays of element 105, the researchers aimed to observe the spontaneous fission (SF) of the element and study the resulting fission fragments. They published a paper in February 1970, reporting multiple examples of two such activities, with half-lives of 14 ms and . They assigned the former activity to 242mfAm and ascribed the latter activity to an isotope of element 105. They suggested that it was unlikely that this activity could come from a transfer reaction instead of element 105, because the yield ratio for this reaction was significantly lower than that of the 242mfAm-producing transfer reaction, in accordance with theoretical predictions. To establish that this activity was not from a (22Ne,xn) reaction, the researchers bombarded a 243Am target with 18O ions; reactions producing 256103 and 257103 showed very little SF activity (matching the established data), and the reaction producing heavier 258103 and 259103 produced no SF activity at all, in line with theoretical data. The researchers concluded that the activities observed came from SF of element 105.
JINR then attempted an experiment to create element 105, published in a report in May 1970. They claimed that they had synthesized more nuclei of element 105 and that the experiment confirmed their previous work. According to the paper, the isotope produced by JINR was probably 261105, or possibly 260105. This report included an initial chemical examination: the thermal gradient version of the gas-chromatography method was applied to demonstrate that the chloride of what had formed from the SF activity nearly matched that of niobium pentachloride, rather than hafnium tetrachloride. The team identified a 2.2-second SF activity in a volatile chloride portraying eka-tantalum properties, and inferred that the source of the SF activity must have been element 105.
In June 1970, JINR made improvements on their first experiment, using a purer target and reducing the intensity of transfer reactions by installing a collimator before the catcher. This time, they were able to find 9.1 MeV alpha activities with daughter isotopes identifiable as either 256103 or 257103, implying that the original isotope was either 260105 or 261105.
A controversy erupted on who had discovered the element, which each group suggesting its own name: the Dubna group named the element nielsbohrium after Niels Bohr, while the Berkeley group named it hahnium after Otto Hahn. Eventually a joint working party of IUPAC and IUPAP, the Transfermium Working Group, decided that credit for the discovery should be shared. After various compromises were attempted, where element 105 was called kurchatovium, joliotium and hahnium, in 1997 IUPAC officially named the element dubnium after Dubna, and nielsbohrium was eventually simplified to bohrium and used for element 107.
Chemical properties
Like other groups, the members of this family show patterns in its electron configuration, especially the outermost shells. (The expected 4d3 5s2 configuration for niobium is a very low-lying excited state at about 0.14 eV.)NIST Atomic Spectra Database
+ Electron configurations of group 5 elements Element Electrons per shell Electron configuration 23 V, vanadium 41 Nb, niobium 73 Ta, tantalum 105 Db, dubnium
Most of the chemistry has been observed only for the first three members of the group (the chemistry of dubnium is not very established, but what is known appears to match expectations for a heavier congener of tantalum). All the elements of the group are reactive metals with a high melting points (1910 °C, 2477 °C, 3017 °C). The reactivity is not always obvious due to the rapid formation of a stable oxide layer, which prevents further reactions, similarly to trends in group 3 or group 4. The metals form different oxides: vanadium forms vanadium(II) oxide, vanadium(III) oxide, vanadium(IV) oxide and vanadium(V) oxide, niobium forms niobium(II) oxide, niobium(IV) oxide and niobium(V) oxide, but out of tantalum oxides only tantalum(V) oxide is characterized. Metal(V) oxides are generally nonreactive and act like acids rather than bases, but the lower oxides are less stable. They, however, have some unusual properties for oxides, such as high electric conductivity.
All three elements form various inorganic compounds, generally in the oxidation state of +5. Lower oxidation states are also known, but in all elements other than vanadium, they are less stable, decreasing in stability with atomic mass increase.
Compounds
Oxides Vanadium forms oxides in the +2, +3, +4 and +5 oxidation states, forming vanadium(II) oxide (VO), vanadium(III) oxide (V2O3), vanadium(IV) oxide (VO2) and vanadium(V) oxide (V2O5). Vanadium(V) oxide or vanadium pentoxide is the most common, being precursor to most alloys and compounds of vanadium, and is also a widely used industrial catalyst.
Niobium forms oxides in the oxidation states +5 (), +4 (), and the rarer oxidation state, +2 (NbO). Most common is the pentoxide, also being precursor to almost all niobium compounds and alloys.
Tantalum pentoxide (Ta2O5) is the most important compound from the perspective of applications. Oxides of tantalum in lower oxidation states are numerous, including many defect structures, and are lightly studied or poorly characterized.
Oxyanions
In aqueous solution, vanadium(V) forms an extensive family of oxyanions as established by 51V NMR spectroscopy. The interrelationships in this family are described by the predominance diagram, which shows at least 11 species, depending on pH and concentration. The tetrahedral orthovanadate ion, , is the principal species present at pH 12–14. Similar in size and charge to phosphorus(V), vanadium(V) also parallels its chemistry and crystallography. Orthovanadate V is used in protein crystallography to study the biochemistry of phosphate. Beside that, this anion also has been shown to interact with activity of some specific enzymes. The tetrathiovanadate [VS4]3− is analogous to the orthovanadate ion.