Group 4 element

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Group 4 in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
group 3 ←  → group 5
IUPAC group number 4
Name by elementtitanium group
CAS group number
(US, pattern A-B-A)
IVB
old IUPAC number
(Europe, pattern A-B)
IVA
↓  Period
4
Titan-crystal bar.JPG
Titanium (Ti)
22 Transition metal
5
Zirconium crystal bar and 1cm3 cube.jpg
Zirconium (Zr)
40 Transition metal
6
Hf-crystal bar.jpg
Hafnium (Hf)
72 Transition metal
7 Rutherfordium (Rf)
104 Transition metal
Legend

Group 4 is the second group of transition metals in the periodic table. It contains the four elements titanium (Ti), zirconium (Zr), hafnium (Hf), and rutherfordium (Rf). The group is also called the titanium group or titanium family after its lightest member.

Contents

As is typical for early transition metals, zirconium and hafnium have only the group oxidation state of +4 as a major one, and are quite electropositive and have a less rich coordination chemistry. Due to the effects of the lanthanide contraction, they are very similar in properties. Titanium is somewhat distinct due to its smaller size: it has a well-defined +3 state as well (although +4 is more stable).

All the group 4 elements are hard, refractory metals. Their inherent reactivity is completely masked due to the formation of a dense oxide layer that protects them from corrosion, as well as attack by many acids and alkalis. The first three of them occur naturally. Rutherfordium is strongly radioactive: it does not occur naturally and must be produced by artificial synthesis, but its observed and theoretically predicted properties are consistent with it being a heavier homologue of hafnium. None of them have any biological role.

History

Zircon was known as a gemstone from ancient times, [1] but it was not known to contain a new element until the work of German chemist Martin Heinrich Klaproth in 1789. He analysed the zircon-containing mineral jargoon and found a new earth (oxide), but was unable to isolate the element from its oxide. Cornish chemist Humphry Davy also attempted to isolate this new element in 1808 through electrolysis, but failed: he gave it the name zirconium. [2] In 1824, Swedish chemist Jöns Jakob Berzelius isolated an impure form of zirconium, obtained by heating a mixture of potassium and potassium zirconium fluoride in an iron tube. [1]

Cornish mineralogist William Gregor first identified titanium in ilmenite sand beside a stream in Cornwall, Great Britain in the year 1791. [3] After analyzing the sand, he determined the weakly magnetic sand to contain iron oxide and a metal oxide that he could not identify. [4] During that same year, mineralogist Franz Joseph Muller produced the same metal oxide and could not identify it. In 1795, chemist Martin Heinrich Klaproth independently rediscovered the metal oxide in rutile from the Hungarian village Boinik. [3] He identified the oxide containing a new element and named it for the Titans of Greek mythology. [5] Berzelius was also the first to prepare titanium metal (albeit impurely), doing so in 1825. [6]

The X-ray spectroscopy done by Henry Moseley in 1914 showed a direct dependency between spectral line and effective nuclear charge. This led to the nuclear charge, or atomic number of an element, being used to ascertain its place within the periodic table. With this method, Moseley determined the number of lanthanides and showed that there was a missing element with atomic number 72. [7] This spurred chemists to look for it. [8] Georges Urbain asserted that he found element 72 in the rare earth elements in 1907 and published his results on celtium in 1911. [9] Neither the spectra nor the chemical behavior he claimed matched with the element found later, and therefore his claim was turned down after a long-standing controversy. [10]

By early 1923, several physicists and chemists such as Niels Bohr [11] and Charles Rugeley Bury [12] suggested that element 72 should resemble zirconium and therefore was not part of the rare earth elements group. These suggestions were based on Bohr's theories of the atom, the X-ray spectroscopy of Moseley, and the chemical arguments of Friedrich Paneth. [13] [14] Encouraged by this, and by the reappearance in 1922 of Urbain's claims that element 72 was a rare earth element discovered in 1911, Dirk Coster and Georg von Hevesy were motivated to search for the new element in zirconium ores. [15] Hafnium was discovered by the two in 1923 in Copenhagen, Denmark. [16] [17] The place where the discovery took place led to the element being named for the Latin name for "Copenhagen", Hafnia, the home town of Niels Bohr. [18]

Hafnium was separated from zirconium through repeated recrystallization of the double ammonium or potassium fluorides by Valdemar Thal Jantzen and von Hevesy. [19] Anton Eduard van Arkel and Jan Hendrik de Boer were the first to prepare metallic hafnium by passing hafnium tetraiodide vapor over a heated tungsten filament in 1924. [20] [21] The long delay between the discovery of the lightest two group 4 elements and that of hafnium was partly due to the rarity of hafnium, and partly due to the extreme similarity of zirconium and hafnium, so that all previous samples of zirconium had in reality been contaminated with hafnium without anyone knowing. [22]

The last element of the group, rutherfordium, does not occur naturally and had to be made by synthesis. The first reported detection was by a team at the Joint Institute for Nuclear Research (JINR), which in 1964 claimed to have produced the new element by bombarding a plutonium-242 target with neon-22 ions, although this was later put into question. [23] More conclusive evidence was obtained by researchers at the University of California, Berkeley, who synthesised element 104 in 1969 by bombarding a californium-249 target with carbon-12 ions. [24] A controversy erupted on who had discovered the element, which each group suggesting its own name: the Dubna group named the element kurchatovium after Igor Kurchatov, while the Berkeley group named it rutherfordium after Ernest Rutherford. [25] 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, in 1997, IUPAC officially named the element rutherfordium following the American proposal. [26]

Characteristics

Chemical

Electron configurations of the group 4 elements
ZElementElectron configuration
22Ti, titanium2, 8, 10,  2[Ar]      3d2 4s2
40Zr, zirconium2, 8, 18, 10,  2[Kr]      4d2 5s2
72Hf, hafnium2, 8, 18, 32, 10,  2[Xe] 4f14 5d2 6s2
104Rf, rutherfordium2, 8, 18, 32, 32, 10, 2[Rn] 5f14 6d2 7s2

Like other groups, the members of this family show patterns in their electron configurations, especially the outermost shells, resulting in trends in chemical behavior. Most of the chemistry has been observed only for the first three members of the group; chemical properties of rutherfordium are not well-characterized, but what is known and predicted matches its position as a heavier homolog of hafnium. [27]

Titanium, zirconium, and hafnium are reactive metals, but this is masked in the bulk form because they form a dense oxide layer that sticks to the metal and reforms even if removed. As such, the bulk metals are very resistant to chemical attack; most aqueous acids have no effect unless heated, and aqueous alkalis have no effect even when hot. Oxidizing acids such as nitric acids indeed tend to reduce reactivity as they induce the formation of this oxide layer. The exception is hydrofluoric acid, as it forms soluble fluoro complexes of the metals. When finely divided, their reactivity shows as they become pyrophoric, directly reacting with oxygen and hydrogen, and even nitrogen in the case of titanium. All three are fairly electropositive, although less so than their predecessors in group 3. [28] The oxides TiO2, ZrO2 and HfO2 are white solids with high melting points and unreactive against most acids. [29]

The chemistry of group 4 elements is dominated by the group oxidation state. Zirconium and hafnium are in particular extremely similar, with the most salient differences being physical rather than chemical (melting and boiling points of compounds and their solubility in solvents). [29] This is an effect of the lanthanide contraction: the expected increase of atomic radius from the 4d to the 5d elements is wiped out by the insertion of the 4f elements before. Titanium, being smaller, is distinct from these two: its oxide is less basic than those of zirconium and hafnium, and its aqueous chemistry is more hydrolyzed. [28] Rutherfordium should have a still more basic oxide than zirconium and hafnium. [30]

The chemistry of all three is dominated by the +4 oxidation state, though this is too high to be well-described as totally ionic. Low oxidation states are not well-represented for zirconium and hafnium [28] (and should be even less well-represented for rutherfordium); [30] the +3 oxidation state of zirconium and hafnium reduces water. For titanium, this oxidation state is merely easily oxidised, forming a violet Ti3+ aqua cation in solution. The elements have a significant coordination chemistry: zirconium and hafnium are large enough to readily support the coordination number of 8. All three metals however form weak sigma bonds to carbon and because they have few d electrons, pi backbonding is not very effective either. [28]

Physical

The trends in group 4 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 refractory metals, though impurities of carbon, nitrogen, and oxygen make them brittle. [31] They all crystallize in the hexagonal close-packed structure at room temperature, [32] and rutherfordium is expected to do the same. [33] At high temperatures, titanium, zirconium, and hafnium transform to a body-centered cubic structure. While they are better conductors of heat and electricity than their group 3 predecessors, they are still poor compared to most metals. This, along with the higher melting and boiling points, and enthalpies of fusion, vaporization, and atomization, reflects the extra d electron available for metallic bonding. [32]

The table below is a summary of the key physical properties of the group 4 elements. The four question-marked values are extrapolated. [34]

Properties of the group 4 elements
NameTi, titanium Zr, zirconium Hf, hafnium Rf, rutherfordium
Melting point 1941 K (1668 °C)2130 K (1857 °C)2506 K (2233 °C)2400 K (2100 °C)?
Boiling point 3560 K (3287 °C)4682 K (4409 °C)4876 K (4603 °C)5800 K (5500 °C)?
Density 4.507 g·cm−36.511 g·cm−313.31 g·cm−317 g·cm−3?
Appearancesilver metallicsilver whitesilver gray ?
Atomic radius 140 pm155 pm155 pm150 pm?

Titanium

As a metal, titanium is recognized for its high strength-to-weight ratio. [35] It is a strong metal with low density that is quite ductile (especially in an oxygen-free environment), [36] lustrous, and metallic-white in color. [37] Due to its relatively high melting point (1,668 °C or 3,034 °F) it has sometimes been described as a refractory metal, but this is not the case. [38] It is paramagnetic and has fairly low electrical and thermal conductivity compared to other metals. [36] Titanium is superconducting when cooled below its critical temperature of 0.49 K. [39] [40]

Zirconium

Zirconium is a lustrous , greyish-white, soft, ductile, malleable metal that is solid at room temperature, though it is hard and brittle at lesser purities. [2] In powder form, zirconium is highly flammable, but the solid form is much less prone to ignition. Zirconium is highly resistant to corrosion by alkalis, acids, salt water and other agents. [1] However, it will dissolve in hydrochloric and sulfuric acid , especially when fluorine is present. [41] Alloys with zinc are magnetic at less than 35 K. [1]

Hafnium

Hafnium is a shiny, silvery, ductile metal that is corrosion-resistant and chemically similar to zirconium [42] in that they have the same number of valence electrons and are in the same group. Also, their relativistic effects are similar: The expected expansion of atomic radii from period 5 to 6 is almost exactly canceled out by the lanthanide contraction. Hafnium changes from its alpha form, a hexagonal close-packed lattice, to its beta form, a body-centered cubic lattice, at 2388 K. [43] The physical properties of hafnium metal samples are markedly affected by zirconium impurities, especially the nuclear properties, as these two elements are among the most difficult to separate because of their chemical similarity. [42]

Rutherfordium

Rutherfordium is expected to be a solid under normal conditions and have a hexagonal close-packed crystal structure (c/a = 1.61), similar to its lighter congener hafnium. [33] It should be a metal with density ~17 g/cm3. [44] [45] The atomic radius of rutherfordium is expected to be ~150  pm. Due to relativistic stabilization of the 7s orbital and destabilization of the 6d orbital, Rf+ and Rf2+ ions are predicted to give up 6d electrons instead of 7s electrons, which is the opposite of the behavior of its lighter homologs. [34] When under high pressure (variously calculated as 72 or ~50 GPa), rutherfordium is expected to transition to body-centered cubic crystal structure; hafnium transforms to this structure at 71±1 GPa, but has an intermediate ω structure that it transforms to at 38±8 GPa that should be lacking for rutherfordium. [46]

Production

The production of the metals itself is difficult due to their reactivity. The formation of oxides, nitrides, and carbides must be avoided to yield workable metals; this is normally achieved by the Kroll process. The oxides (MO2) are reacted with coal and chlorine to form the chlorides (MCl4). The chlorides of the metals are then reacted with magnesium, yielding magnesium chloride and the metals.

Further purification is done by a chemical transport reaction developed by Anton Eduard van Arkel and Jan Hendrik de Boer. In a closed vessel, the metal reacts with iodine at temperatures above 500 °C forming metal(IV) iodide; at a tungsten filament of nearly 2000 °C the reverse reaction happens and the iodine and metal are set free. The metal forms a solid coating on the tungsten filament and the iodine can react with additional metal resulting in a steady turnover. [29] [21]

M + 2 I2 (low temp.) → MI4
MI4 (high temp.) → M + 2 I2

Occurrence

Heavy minerals (dark) in a quartz beach sand (Chennai, India). HeavyMineralsBeachSand.jpg
Heavy minerals (dark) in a quartz beach sand (Chennai, India).

The abundance of the group 4 metals decreases with increase of atomic mass. Titanium is the seventh most abundant metal in Earth's crust and has an abundance of 6320 ppm, while zirconium has an abundance of 162 ppm and hafnium has only an abundance of 3 ppm. [47]

All three stable elements occur in heavy mineral sands ore deposits, which are placer deposits formed, most usually in beach environments, by concentration due to the specific gravity of the mineral grains of erosion material from mafic and ultramafic rock. The titanium minerals are mostly anatase and rutile, and zirconium occurs in the mineral zircon. Because of the chemical similarity, up to 5% of the zirconium in zircon is replaced by hafnium. The largest producers of the group 4 elements are Australia, South Africa and Canada. [48] [49] [50] [51] [52]

Applications

Titanium metal and its alloys have a wide range of applications, where the corrosion resistance, the heat stability and the low density (light weight) are of benefit. The foremost use of corrosion-resistant hafnium and zirconium has been in nuclear reactors. Zirconium has a very low and hafnium has a high thermal neutron-capture cross-section. Therefore, zirconium (mostly as zircaloy) is used as cladding of fuel rods in nuclear reactors, [42] while hafnium is used in control rods for nuclear reactors, because each hafnium atom can absorb multiple neutrons. [53] [54]

Smaller amounts of hafnium [55] and zirconium are used in super alloys to improve the properties of those alloys. [56]

Biological occurrences

The group 4 elements are hard refractory metals with low aqueous solubility and low availability to the biosphere. Titanium and zirconium are relatively abundant, whereas hafnium and rutherfordium are rare to non-existent in the environment.

Titanium has no known role in any organism's biology. However, many studies suggest that titanium could be biologically active. Most titanium on Earth is stored within insoluble minerals, so it is unlikely to be a part of any biological system in spite of being potentially biologically active. [57]

Zirconium plays no known role in any biological system, [58] but is common in biological systems. Certain antiperspirant products use Aluminium zirconium tetrachlorohydrex gly to block sweat pores in the skin. [59]

Hafnium plays no known role in any biological system, and has low toxicity. [60]

Rutherfordium is synthetic, expensive, and radioactive: the most stable isotopes have half-lives under an hour. Few chemical properties and no biological functions are known.

Precautions

Titanium is non-toxic even in large doses and does not play any natural role inside the human body. [61] An estimated quantity of 0.8 milligrams of titanium is ingested by humans each day, but most passes through without being absorbed in the tissues. [61] It does, however, sometimes bio-accumulate in tissues that contain silica. One study indicates a possible connection between titanium and yellow nail syndrome. [62]

Zirconium powder can cause irritation, but only contact with the eyes requires medical attention. [63] OSHA recommendations for zirconium are 5 mg/m3 time weighted average limit and a 10 mg/m3 short-term exposure limit. [64]

Only limited data exists on the toxicology of hafnium. [65] Care needs to be taken when machining hafnium because it is pyrophoric—fine particles can spontaneously combust when exposed to air. Compounds that contain this metal are rarely encountered by most people. The pure metal is not considered toxic, but hafnium compounds should be handled as if they were toxic because the ionic forms of metals are normally at greatest risk for toxicity, and limited animal testing has been done for hafnium compounds. [65]

Related Research Articles

Dubnium is a synthetic chemical element; it has symbol Db and atomic number 105. It is highly radioactive: the most stable known isotope, dubnium-268, has a half-life of about 16 hours. This greatly limits extended research on the element.

Hafnium is a chemical element; it has symbol Hf and atomic number 72. A lustrous, silvery gray, tetravalent transition metal, hafnium chemically resembles zirconium and is found in many zirconium minerals. Its existence was predicted by Dmitri Mendeleev in 1869, though it was not identified until 1922, by Dirk Coster and George de Hevesy. Hafnium is named after Hafnia, the Latin name for Copenhagen, where it was discovered.

<span class="mw-page-title-main">Niobium</span> Chemical element with atomic number 41 (Nb)

Niobium is a chemical element; it has symbol Nb and atomic number 41. It is a light grey, crystalline, and ductile transition metal. Pure niobium has a Mohs hardness rating similar to pure titanium, and it has similar ductility to iron. Niobium oxidizes in Earth's atmosphere very slowly, hence its application in jewelry as a hypoallergenic alternative to nickel. Niobium is often found in the minerals pyrochlore and columbite. Its name comes from Greek mythology: Niobe, daughter of Tantalus, the namesake of tantalum. The name reflects the great similarity between the two elements in their physical and chemical properties, which makes them difficult to distinguish.

<span class="mw-page-title-main">Periodic table</span> Tabular arrangement of the chemical elements ordered by atomic number

The periodic table, also known as the periodic table of the elements, is an ordered arrangement of the chemical elements into rows ("periods") and columns ("groups"). It is an icon of chemistry and is widely used in physics and other sciences. It is a depiction of the periodic law, which states that when the elements are arranged in order of their atomic numbers an approximate recurrence of their properties is evident. The table is divided into four roughly rectangular areas called blocks. Elements in the same group tend to show similar chemical characteristics.

<span class="mw-page-title-main">Ruthenium</span> Chemical element with atomic number 44 (Ru)

Ruthenium is a chemical element; it has symbol Ru and atomic number 44. It is a rare transition metal belonging to the platinum group of the periodic table. Like the other metals of the platinum group, ruthenium is unreactive to most chemicals. Karl Ernst Claus, a Russian scientist of Baltic-German ancestry, discovered the element in 1844 at Kazan State University and named it in honor of Russia, using the Latin name Ruthenia. Ruthenium is usually found as a minor component of platinum ores; the annual production has risen from about 19 tonnes in 2009 to some 35.5 tonnes in 2017. Most ruthenium produced is used in wear-resistant electrical contacts and thick-film resistors. A minor application for ruthenium is in platinum alloys and as a chemistry catalyst. A new application of ruthenium is as the capping layer for extreme ultraviolet photomasks. Ruthenium is generally found in ores with the other platinum group metals in the Ural Mountains and in North and South America. Small but commercially important quantities are also found in pentlandite extracted from Sudbury, Ontario, and in pyroxenite deposits in South Africa.

Rutherfordium is a synthetic chemical element; it has symbol Rf and atomic number 104. It is named after physicist Ernest Rutherford. As a synthetic element, it is not found in nature and can only be made in a particle accelerator. It is radioactive; the most stable known isotope, 267Rf, has a half-life of about 48 minutes.

<span class="mw-page-title-main">Scandium</span> Chemical element with atomic number 21 (Sc)

Scandium is a chemical element with the symbol Sc and atomic number 21. It is a silvery-white metallic d-block element. Historically, it has been classified as a rare-earth element, together with yttrium and the lanthanides. It was discovered in 1879 by spectral analysis of the minerals euxenite and gadolinite from Scandinavia.

<span class="mw-page-title-main">Titanium</span> Chemical element with atomic number 22 (Ti)

Titanium is a chemical element; it has symbol Ti and atomic number 22. Found in nature only as an oxide, it can be reduced to produce a lustrous transition metal with a silver color, low density, and high strength, resistant to corrosion in sea water, aqua regia, and chlorine.

<span class="mw-page-title-main">Thorium</span> Chemical element with atomic number 90 (Th)

Thorium is a chemical element; it has symbol Th and atomic number 90. Thorium is a weakly radioactive light silver metal which tarnishes olive grey when it is exposed to air, forming thorium dioxide; it is moderately soft, malleable, and has a high melting point. Thorium is an electropositive actinide whose chemistry is dominated by the +4 oxidation state; it is quite reactive and can ignite in air when finely divided.

<span class="mw-page-title-main">Zirconium</span> Chemical element with atomic number 40 (Zr)

Zirconium is a chemical element; it has symbol Zr and atomic number 40. First identified in 1789, isolated in impure form in 1824, and manufactured at scale by 1925, pure zirconium is a lustrous transition metal with a greyish-white color that closely resembles hafnium and, to a lesser extent, titanium. It is solid at room temperature, ductile, malleable and corrosion-resistant. The name zirconium is derived from the name of the mineral zircon, the most important source of zirconium. The word is related to Persian zargun. Besides zircon, zirconium occurs in over 140 other minerals, including baddeleyite and eudialyte; most zirconium is produced as a byproduct of minerals mined for titanium and tin.

A period 5 element is one of the chemical elements in the fifth row of the periodic table of the chemical elements. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical behaviour begins to repeat, meaning that elements with similar behaviour fall into the same vertical columns. The fifth period contains 18 elements, beginning with rubidium and ending with xenon. As a rule, period 5 elements fill their 5s shells first, then their 4d, and 5p shells, in that order; however, there are exceptions, such as rhodium.

A period 6 element is one of the chemical elements in the sixth row (or period) of the periodic table of the chemical elements, including the lanthanides. The periodic table is laid out in rows to illustrate recurring (periodic) trends in the chemical behaviour of the elements as their atomic number increases: a new row is begun when chemical behaviour begins to repeat, meaning that elements with similar behaviour fall into the same vertical columns. The sixth period contains 32 elements, tied for the most with period 7, beginning with caesium and ending with radon. Lead is currently the last stable element; all subsequent elements are radioactive. For bismuth, however, its only primordial isotope, 209Bi, has a half-life of more than 1019 years, over a billion times longer than the current age of the universe. As a rule, period 6 elements fill their 6s shells first, then their 4f, 5d, and 6p shells, in that order; however, there are exceptions, such as gold.

Chemistry is the physical science concerned with the composition, structure, and properties of matter, as well as the changes it undergoes during chemical reactions.

<span class="mw-page-title-main">Group 3 element</span> Group of chemical elements

Group 3 is the first group of transition metals in the periodic table. This group is closely related to the rare-earth elements. It contains the four elements scandium (Sc), yttrium (Y), lutetium (Lu), and lawrencium (Lr). The group is also called the scandium group or scandium family after its lightest member.

<span class="mw-page-title-main">Group 5 element</span> Group of elements in the periodic table

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.

The lanthanide contraction is the greater-than-expected decrease in atomic radii and ionic radii of the elements in the lanthanide series, from left to right. It is caused by the poor shielding effect of nuclear charge by the 4f electrons along with the expected periodic trend of increasing electronegativity and nuclear charge on moving from left to right. About 10% of the lanthanide contraction has been attributed to relativistic effects.

<span class="mw-page-title-main">Hafnium tetrachloride</span> Chemical compound

Hafnium(IV) chloride is the inorganic compound with the formula HfCl4. This colourless solid is the precursor to most hafnium organometallic compounds. It has a variety of highly specialized applications, mainly in materials science and as a catalyst.

<span class="mw-page-title-main">Zirconium(IV) chloride</span> Chemical compound

Zirconium(IV) chloride, also known as zirconium tetrachloride, is an inorganic compound frequently used as a precursor to other compounds of zirconium. This white high-melting solid hydrolyzes rapidly in humid air.

<span class="mw-page-title-main">Yttrium</span> Chemical element with atomic number 39 (Y)

Yttrium is a chemical element; it has symbol Y and atomic number 39. It is a silvery-metallic transition metal chemically similar to the lanthanides and has often been classified as a "rare-earth element". Yttrium is almost always found in combination with lanthanide elements in rare-earth minerals and is never found in nature as a free element. 89Y is the only stable isotope and the only isotope found in the Earth's crust.

Hafnium compounds are compounds containing the element hafnium (Hf). Due to the lanthanide contraction, the ionic radius of hafnium(IV) (0.78 ångström) is almost the same as that of zirconium(IV) (0.79 angstroms). Consequently, compounds of hafnium(IV) and zirconium(IV) have very similar chemical and physical properties. Hafnium and zirconium tend to occur together in nature and the similarity of their ionic radii makes their chemical separation rather difficult. Hafnium tends to form inorganic compounds in the oxidation state of +4. Halogens react with it to form hafnium tetrahalides. At higher temperatures, hafnium reacts with oxygen, nitrogen, carbon, boron, sulfur, and silicon. Some compounds of hafnium in lower oxidation states are known.

References

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