Group 5 element
Group 5 in the periodic table | |||||||||
---|---|---|---|---|---|---|---|---|---|
| |||||||||
↓ Period | |||||||||
4 | Vanadium (V) 23 Transition metal | ||||||||
5 | Niobium (Nb) 41 Transition metal | ||||||||
6 | Tantalum (Ta) 73 Transition metal | ||||||||
7 | Dubnium (Db) 105 Transition metal | ||||||||
Legend
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Group 5 is a
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
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
In 1831 Swedish chemist
Niobium and tantalum
Niobium was
Subsequently, there was considerable confusion[13] over the difference between columbium (niobium) and the closely related tantalum. In 1809, English chemist William Hyde Wollaston compared the oxides derived from both columbium—columbite, with a density 5.918 g/cm3, and tantalum—tantalite, with a density over 8 g/cm3, and concluded that the two oxides, despite the significant difference in density, were identical; thus he kept the name tantalum.[13] 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).[14][15] This confusion arose from the minimal observed differences between tantalum and niobium. The claimed new elements pelopium, ilmenium, and dianium[16] were in fact identical to niobium or mixtures of niobium and tantalum.[17] Pure tantalum was not produced until 1903.[18]
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.[19]
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 2.2±0.5 s. They assigned the former activity to 242mfAm[a] 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.[19]
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.[19] 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.[19]
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.[19]
A
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.)[22]
Electron configurations of the group 5 elements | |||
---|---|---|---|
Z | Element | No. of electrons/shell | Electron configuration |
23 | V, vanadium | 2, 8, 11, 2 | [Ar] 3d3 4s2 |
41 | Nb, niobium | 2, 8, 18, 12, 1 | [Kr] 4d4 5s1 |
73 | Ta, tantalum | 2, 8, 18, 32, 11, 2 | [Xe] 4f14 5d3 6s2 |
105 | Db, dubnium | 2, 8, 18, 32, 32, 11, 2 | [Rn] 5f14 6d3 7s2 |
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
All three elements form various inorganic compounds, generally in the oxidation state of +5. Lower oxidation states are also known, but 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.[24]
Niobium forms oxides in the oxidation states +5 (Nb2O5),[25] +4 (NbO2), and the rarer oxidation state, +2 (NbO).[26] Most common is the pentoxide, also being precursor to almost all niobium compounds and alloys.[23][27]
Oxyanions
In aqueous solution, vanadium(V) forms an extensive family of
At lower pH values, the monomer [HVO4]2− and dimer [V2O7]4− are formed, with the monomer predominant at vanadium concentration of less than c. 10−2M (pV > 2, where pV is equal to the minus value of the logarithm of the total vanadium concentration/M). The formation of the divanadate ion is analogous to the formation of the
- 10 [VO4]3− + 24 H+ → [V10O28]6− + 12 H2O
In decavanadate, each V(V) center is surrounded by six oxide ligands.[23] Vanadic acid, H3VO4 exists only at very low concentrations because protonation of the tetrahedral species [H2VO4]− results in the preferential formation of the octahedral [VO2(H2O)4]+ species. In strongly acidic solutions, pH < 2, [VO2(H2O)4]+ is the predominant species, while the oxide V2O5 precipitates from solution at high concentrations. The oxide is formally the acid anhydride of vanadic acid. The structures of many vanadate compounds have been determined by X-ray crystallography.
Vanadium(V) forms various peroxo complexes, most notably in the active site of the vanadium-containing
Niobates are generated by dissolving the pentoxide in basic hydroxide solutions or by melting it in alkali metal oxides. Examples are lithium niobate (LiNbO3) and lanthanum niobate (LaNbO4). In the lithium niobate is a trigonally distorted perovskite-like structure, whereas the lanthanum niobate contains lone NbO3−
4 ions.[23]
Tantalates, compounds containing [TaO4]3− or [TaO3]− are numerous. Lithium tantalate (LiTaO3) adopts a perovskite structure. Lanthanum tantalate (LaTaO4) contains isolated TaO3−
4 tetrahedra.[23]
Halides and their derivatives
Twelve binary
Many vanadium
) are the most widely studied. Akin to POCl3, they are volatile, adopt tetrahedral structures in the gas phase, and are Lewis acidic.Niobium forms halides in the oxidation states of +5 and +4 as well as diverse
Anionic halide compounds of niobium are well known, owing in part to the
- Nb2Cl10 + 2 Cl− → 2 [NbCl6]−
As with other metals with low atomic numbers, a variety of reduced halide cluster ions is known, the prime example being [Nb6Cl18]4−.[26]
Tantalum halides span the oxidation states of +5, +4, and +3.
Physical properties
The trends in group 5 follow those of the other early d-block groups and reflect the addition of a filled f-shell into the core in passing from the fifth to the sixth period. All the stable members of the group are silvery-blue
The table below is a summary of the key physical properties of the group 5 elements. The question-marked value is predicted.[45]
Name | V, vanadium | Nb, niobium | Ta, tantalum | Db, dubnium |
---|---|---|---|---|
Melting point | 2183 K (1910 °C) | 2750 K (2477 °C) | 3290 K (3017 °C) | Unknown |
Boiling point | 3680 K (3407 °C) | 5017 K (4744 °C) | 5731 K (5458 °C) | Unknown |
Density | 6.11 g·cm−3 | 8.57 g·cm−3 | 16.69 g·cm−3 | 21.6 g·cm−3?[46][47] |
Appearance | blue-silver-gray metal | grayish metallic, blue when oxidized | gray blue | Unknown |
Atomic radius | 135 pm | 146 pm | 146 pm | 139 pm |
Vanadium
Vanadium is an average-hard,
Niobium
Niobium is a lustrous, grey, ductile, paramagnetic metal in group 5 of the periodic table (see table), with an electron configuration in the outermost shells atypical for group 5. Similarly atypical configurations occur in the neighborhood of ruthenium (44), rhodium (45), and palladium (46).
Although it is thought to have a
Niobium becomes a
When very pure, it is comparatively soft and ductile, but impurities make it harder.[53]
The metal has a low capture cross-section for thermal neutrons;[54] thus it is used in the nuclear industries where neutron transparent structures are desired.[55]
Tantalum
Tantalum is dark (blue-gray),[56] dense, ductile, very hard, easily fabricated, and highly conductive of heat and electricity. The metal is renowned for its resistance to corrosion by acids; in fact, at temperatures below 150 °C tantalum is almost completely immune to attack by the normally aggressive aqua regia. It can be dissolved with hydrofluoric acid or acidic solutions containing the fluoride ion and sulfur trioxide, as well as with a solution of potassium hydroxide. Tantalum's high melting point of 3017 °C (boiling point 5458 °C) is exceeded among the elements only by tungsten, rhenium and osmium for metals, and carbon.
Tantalum exists in two crystalline phases, alpha and beta. The alpha phase is relatively
Dubnium
A direct relativistic effect is that as the atomic numbers of elements increase, the innermost electrons begin to revolve faster around the nucleus as a result of an increase of
A more indirect effect is that the contracted s and p1/2 orbitals shield the charge of the nucleus more effectively, leaving less for the outer d and f electrons, which therefore move in larger orbitals. Dubnium is greatly affected by this: unlike the previous group 5 members, its 7s electrons are slightly more difficult to extract than its 6d electrons.[45]
Another effect is the spin–orbit interaction, particularly spin–orbit splitting, which splits the 6d subshell—the azimuthal quantum number ℓ of a d shell is 2—into two subshells, with four of the ten orbitals having their ℓ lowered to 3/2 and six raised to 5/2. All ten energy levels are raised; four of them are lower than the other six. (The three 6d electrons normally occupy the lowest energy levels, 6d3/2.)[45]
A single ionized atom of dubnium (Db+) should lose a 6d electron compared to a neutral atom; the doubly (Db2+) or triply (Db3+) ionized atoms of dubnium should eliminate 7s electrons, unlike its lighter homologs. Despite the changes, dubnium is still expected to have five valence electrons; 7p energy levels have not been shown to influence dubnium and its properties. As the 6d orbitals of dubnium are more destabilized than the 5d ones of tantalum, and Db3+ is expected to have two 6d, rather than 7s, electrons remaining, the resulting +3 oxidation state is expected to be unstable and even rarer than that of tantalum. The ionization potential of dubnium in its maximum +5 oxidation state should be slightly lower than that of tantalum and the ionic radius of dubnium should increase compared to tantalum; this has a significant effect on dubnium's chemistry.[45]
Atoms of dubnium in the solid state should arrange themselves in a
Occurrence
There are 160 parts per million of vanadium in the Earth's crust, making it the 19th most abundant element there.
Production
Vanadium
Vanadium metal is obtained by a multistep process that begins with roasting crushed ore with
- 2 V + 3 I2 ⇌ 2 VI3
Most vanadium is used as a component of a steel alloy called ferrovanadium. Ferrovanadium is produced directly by reducing a mixture of vanadium oxide, iron oxides and iron in an electric furnace. The vanadium ends up in pig iron produced from vanadium-bearing magnetite. Depending on the ore used, the slag contains up to 25% of vanadium.[59]
Approximately 70000
Niobium and tantalum
Year | Australia | Brazil | Canada |
---|---|---|---|
2000 | 160 | 30,000 | 2,290 |
2001 | 230 | 22,000 | 3,200 |
2002 | 290 | 26,000 | 3,410 |
2003 | 230 | 29,000 | 3,280 |
2004 | 200 | 29,900 | 3,400 |
2005 | 200 | 35,000 | 3,310 |
2006 | 200 | 40,000 | 4,167 |
2007 | Unknown | 57,300 | 3,020 |
2008 | Unknown | 58,000 | 4,380 |
2009 | Unknown | 58,000 | 4,330 |
2010 | Unknown | 58,000 | 4,420 |
2011 | Unknown | 58,000 | 4,630 |
2012 | Unknown | 63,000 | 5,000 |
2013 | Unknown | 53,100 | 5,260 |
2014 | Unknown | 53,000 | 5,000 |
2015 | Unknown | 58,000 | 5,750 |
2016 | Unknown | 57,000 | 6,100 |
2017 | Unknown | 60,700 | 6,980 |
2018 | Unknown | 59,000 | 7,700 |
2019 | Unknown | 88,900 | 6,800 |
After the separation from the other minerals, the mixed oxides of tantalum Ta2O5 and niobium Nb2O5 are obtained. To produce niobium, the first step in the processing is the reaction of the oxides with hydrofluoric acid:[41]
- Ta2O5 + 14 HF → 2 H2[TaF7] + 5 H2O
- Nb2O5 + 10 HF → 2 H2[NbOF5] + 3 H2O
The first industrial scale separation, developed by
- H2[NbOF5] + 2 KF → K2[NbOF5]↓ + 2 HF
Followed by:
- 2 H2[NbOF5] + 10 NH4OH → Nb2O5↓ + 10 NH4F + 7 H2O
Several methods are used for the
- 3 Nb2O5 + Fe2O3 + 12 Al → 6 Nb + 2 Fe + 6 Al2O3
Small amounts of oxidizers like
As of 2013[update], CBMM from Brazil controlled 85 percent of the world's niobium production.[67] The United States Geological Survey estimates that the production increased from 38,700 tonnes in 2005 to 44,500 tonnes in 2006.[68][69] Worldwide resources are estimated to be 4.4 million tonnes.[69] During the ten-year period between 1995 and 2005, the production more than doubled, starting from 17,800 tonnes in 1995.[70] Between 2009 and 2011, production was stable at 63,000 tonnes per year,[71] with a slight decrease in 2012 to only 50,000 tonnes per year.[72]
Lesser amounts are found in Malawi's Kanyika Deposit (Kanyika mine).
70000 t of tantalum ore are produced yearly. Brazil produces 90% of tantalum ore, with Canada, Australia, China, and Rwanda also producing the element. The demand for tantalum is around 1200 t per year.[18]
Dubnium and beyond
Dubnium is produced synthetically by bombarding
Applications
Vanadium's main application is in alloys, such as
Small amounts of niobium are added to stainless steel to improve its quality. Niobium alloys are also used in rocket nozzles because of niobium's high corrosion resistance.[18]
Tantalum has four main types of applications. Tantalum is added into objects exposed to high temperatures, in
Dubnium has no applications due to its radioactivity, making it highly dangerous to be around.
Biological occurrences
Out of the group 5 elements, only vanadium has been identified as playing a role in the biological chemistry of living systems, but even it plays a very limited role in biology, and is more important in ocean environments than on land.
Vanadium, essential to
Toxicity and precautions
Pure vanadium is not known to be toxic. However,
There is little evidence that vanadium or vanadium compounds are reproductive toxins or
Niobium has no known biological role. While niobium dust is an eye and skin irritant[18] and a potential fire hazard, elemental niobium on a larger scale is physiologically inert (and thus hypoallergenic) and harmless. It is often used in jewelry and has been tested for use in some medical implants.[95][96] Niobium and its compounds thought to be slightly toxic. Short- and long-term exposure to niobates and niobium chloride, two water-soluble chemicals, have been tested in rats. Rats treated with a single injection of niobium pentachloride or niobates show a median lethal dose (LD50) between 10 and 100 mg/kg.[97][98][99] For oral administration the toxicity is lower; a study with rats yielded a LD50 after seven days of 940 mg/kg.[97]
Compounds containing tantalum are rarely encountered in the laboratory, and it and its compounds rarely cause injury, and when they do, the injuries are normally rashes.
Notes
- ^ This notation signifies that the nucleus is a nuclear isomer that decays via spontaneous fission.
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Further reading
- Greenwood, N (2003). "Vanadium to dubnium: from confusion through clarity to complexity". Catalysis Today. 78 (1–4): 5–11. .