Group 12 , with modern IUPAC numbering, is a group of chemical elements in the periodic table. These include zinc (Zn), cadmium (Cd) and mercury (Hg). Further inclusion of copernicium (Cn) in group 12 is supported by recent trials on individual copernicium atoms. Previously this group was named IIB (pronounced as "group of two B", as "II" is a Roman numeral) by CAS and the old IUPAC system.
The three groups of naturally occurring 12 elements are zinc, cadmium and mercury. They are all widely used in electrical and electronic applications, as well as various alloys. The first two members of this group have the same properties because they are solid metal under standard conditions. Mercury is the only metal that is liquid at room temperature. While zinc is very important in the biochemistry of living organisms, cadmium and mercury are both highly toxic. Since copernicium does not occur in nature, it must be synthesized in the laboratory.
Video Group 12 element
Physical and atomic properties
Like other groups of the periodic table, members of group 12 show patterns in their electron configuration, especially the outermost shell, which results in a trend in their chemical behavior:
The group elements 12 are all soft, diamagnetic, divalent metal. They have the lowest melting point among all transition metals. Zinc is bluish-white and shiny, although the most common commercial value of metal has a tedious finishing. Zinc is also referred to in the nonscientific context as spelter . Cadmium is soft, soft, ductile, and with a bluish white color. Mercury is a molten, heavy, silvery-white metal. It is the only common liquid metal at ordinary temperatures, and when compared with other metals, it is a poor conductor of heat, but a fair conductor of electricity.
The table below is a summary of the key physical properties of group 12 elements. Very little is known about copernicium, and none of its physical properties has been confirmed except its boiling point (tentative).
Zinc is somewhat less dense than iron and has a hexagonal crystal structure. The metal is hard and brittle at most temperatures but becomes soft between 100 and 150 ° C. Above 210 ° C, the metal becomes brittle again and can be destroyed by beatings. Zinc is a fair power conductor. For metals, zinc has a relatively low melting (419.5 ° C, 787.1 ° F) and a boiling point (907 ° C). Cadmium is similar in many ways to zinc but forms complex compounds. Unlike other metals, cadmium is resistant to corrosion and as a result is used as a protective coating when deposited on other metals. As a bulk metal, cadmium is insoluble in water and not inflammable; However, in its powder form it can burn and release toxic fumes. Mercury has a very low melting temperature for d-block metals. The full explanation of this fact requires a deep journey into quantum physics, but can be summarized as follows: mercury has a unique electronic configuration in which electrons fill all available 1s, 2s, 2s, 4ps, 4s, 4f, 5s, 5p, 5d and 6s subshell. Because the configuration strongly rejects the removal of electrons, the mercury behaves similarly to the noble gas element, which forms a weak bond and thus easily liquefies the solids. The stability of the 6s shell is due to the presence of a filled 4f shell. A coarse shell filters nuclear charges that increase the attractive Coulomb interaction of the 6s shell and nucleus (see lanthanide contraction). The absence of a shell filled shell is the reason for slightly higher cadmium and zinc temperatures, although the two metals are still easy to melt and, in addition, have an unusually low boiling point. Gold has atoms with one electron 6s smaller than mercury. The electrons are more easily removed and divided between gold atoms form relatively strong metal bonds.
Zinc, cadmium and mercury form a wide variety of alloys. Among those containing zinc, brass is a zinc alloy and copper. Other long-known metals to form binary alloys with zinc are aluminum, antimony, bismuth, gold, iron, lead, mercury, silver, lead, magnesium, cobalt, nickel, tellurium and sodium. While no zinc or zirconium is ferromagnetic, their alloys ZrZn
2 shows ferromagnetism below 35 K. Cadmium is used in various types of solder alloys and bearings, due to low friction coefficient and fatigue resistance. It is also found in some of the lowest melting alloys, such as Wood metal. Because it is a liquid, mercury dissolves other metals and the formed alloy is called amalgam. For example, such amalgam is known as gold, zinc, sodium, and many other metals. Because iron is an exception, iron gourds are traditionally used to trade mercury. Other metals that do not form amalgam with mercury include tantalum, tungsten and platinum. Sodium amalgam is a general reducing agent in organic synthesis, and is also used in high pressure sodium lamps. Mercury is ready to combine with aluminum to form amalgam aluminum mercury when two pure metals come into contact. Because the amalgam reacts with air to produce aluminum oxide, a small amount of corrosion mercury aluminum. For this reason, mercury is not allowed to board aircraft under certain circumstances because that risk forms an amalgam with an open aluminum section on the aircraft.
Maps Group 12 element
Chemistry
Most chemistry has been observed only for the first three members of group 12. The copernium chemistry is not well established and therefore the remaining parts are only related to zinc, cadmium and mercury.
Periodic trends
All elements in this group are metals. The similarity of metal radius of cadmium and mercury is the effect of lanthanide contraction. Thus, the trends in this group are unlike trends in group 2, alkaline earth, where the metal radius rises smoothly from top to bottom groups. All three metals have relatively low melting and boiling points, indicating that the metal bond is relatively weak, with relatively little overlap between the valence band and the conduction band. Thus, zinc is close to the boundary between metalloid and metalloid elements, which are usually placed between gallium and germanium, although gallium participates in semi-conductors such as gallium arsenide.
Zinc and cadmium are electropositive while mercury is not. As a result, zinc and cadmium metal are good reducing agents. The elements of group 12 have an oxidation state 2 in which the ion has a rather stable electronic configuration d 10 , with a full sub-shell. However, mercury can easily be reduced to a state of oxidation 1; usually, as in the Hg 2 Classification
The elements in group 12 are usually regarded as d-block elements, but not transitional elements because of the full d-shell. Some authors classify these elements as the main group elements because the valence electrons are in the ns 2 orbital. Nevertheless, they share many characteristics with neighboring group 11 elements on the periodic table, which is almost universally regarded as a transitional element. For example, zinc has many characteristics with adjacent transition metals, copper. The complex zinc deserves to be included in the Irving-Williams series as zinc forms many complexes with the same stoichiometry as a copper (II) complex, albeit with smaller stability constants. There is little similarity between cadmium and silver as a rare silver compound (II) and what exists is a very strong oxidizer. Similarly, the general oxidation state for gold is 3, which prevents many common chemicals between mercury and gold, although there is a similarity between mercury (I) and gold (I) such as the formation of the dikyano linear complexes, [M (CN)) 2 ] - . According to the IUPAC definition of a transition metal as a element whose atom has an incomplete sub-shell, or which can cause cations with an incomplete sub-shell , zinc and cadmium are not transition metals, while mercury. This is because only mercury is known to have a compound with a higher oxidation rate than 2, in mercury (IV) fluoride (although its existence is disputed, as further experiments attempt to confirm its synthesis can not find evidence of HgF 4 ). However, this classification is based on one very high atypical compound seen in non-equilibrium conditions and is contrary to typical chemistry of mercury, and Jensen has suggested that it would be better to consider mercury as a non-transition metal.
Relationship with alkaline earth metals
Although group 12 lies in the d-block of the 18-column modern periodic table, zinc electrons, cadmium, and (almost always) mercury behaves as nuclear electrons and does not take part in bonds. This behavior is similar to the main group elements, but is very different from the group 11 elements (copper, silver, and gold), which have also filled d-subshells in their land-state electron configuration but behave chemically as transition metals. For example, the bond in chromium (II) sulfide (CrS) involves mainly 3d electrons; that in iron (II) sulfide (FeS) involves 3d and 4s electrons; but zinc sulphide (ZnS) involves only 4s electrons and 3d electrons behave as electrons of the nucleus. Indeed, useful comparisons can be made between their properties and the first two members of group 2, beryllium and magnesium, and in the form of short-term periodic tables, this relationship is illustrated more clearly. For example, zinc and cadmium are similar to beryllium and magnesium in atomic radius, ionic radius, electronegativity, and also in the structure of their binary compounds and their ability to form complex ions with many nitrogen and oxygen ligands, such as complex hydrides and amines. However, beryllium and magnesium are small atoms, unlike heavier alkaline earth metals and such as group 12 elements (which have larger nuclear charges but the same number of valence electrons), and the periodic trends to group 2 of beryllium to radium (similar to alkali metals) is not as smooth as down from beryllium to mercury (which is more similar to the main group of p-block) due to d-block and lanthanide contractions. It is also a contraction of d-blocks and lanthanides that give many of its peculiar properties to mercury.
​​Compound
All three metal ions form many tetrahedral species, such as MCl 2 -
4 . Both zinc and cadmium can also form octahedral complexes such as aqua ions (M (H 2 O) 6 ] 2 which are present in an aqueous salt solution of these metals. The covalent character is achieved by using s orbital and possibly p. Mercury, however, rarely exceeds the coordination number of four. Coordination numbers 2, 3, 5, 7 and 8 are also known.
Extensions
Although copernicium is the twelve strongest known element, there has been some theoretical work on the possibility of heavier group 12 elements. Although a simple extrapolation of the periodic table would place elements of 162, unhexbium (Uhb), under copernicium, relativistic calculations Dirac-Fock predicts that the next 12 element elements after copernicium should be element 164, unhexquadium (Uhq), predicted to have electron configuration ] 5g 18 6f 14 7d 10 8s 2 8p 1/2 2 . Orbital 8s and 8p 1/2 are predicted to be very relativistically stable so that they become core electrons and do not participate in chemical reactions, unlike the previous 12-element group in which electrons act as valence electrons.. However, levels 9 and 9 p 1/2 are expected to be available for hybridization and bonding, so unhexquadium must remain chemically behaving like normal transition metals. Calculations predict that unhexquadium 7d electrons should participate very easily in chemical reactions, so unhexquadium should be able to show stable 6 and 4 oxidation states in addition to the normal state 2 in aqueous solutions with strong ligands. Unhexquadium should therefore be able to form compounds like Uhq (CO) 4 , Uhq (PF 3 ) 4 (both tetrahedral), and Uhq (CN) 2 -
2 (linear), behaviors that are very different from leads, the unhexquadium would be homologous heavier than if not for the effect relativistic. However, divalent conditions will be primary in aqueous solutions, and unhexquadium (II) should behave more similarly to lead than unhexquadium (IV) and unhexquadium (VI).
Unhexquadium should be a soft metal such as mercury, and unhexquadium metal must have a high melting point as it is predicted to be covalent bonded. It is also expected to be a gentle Lewis acid and has the Ahrlands tenderness parameters approaching 4Ã, eV. It should also have some similarities with oganesson as well as to a group of 12 other elements. Unhexquadium must be at least reactive, having the first ionisation energy should be about 685 kJ/mol, proportional to molybdenum. Due to the contraction of lanthanides, actinides, and superactinides, unhexquadium should have a metallic radius of only 158 μm, very close to a much lighter magnesium, although estimated to have an atomic weight of about 474 μm, about 19.5 times as much as magnesium. These small fingers and high weight are expected to have a very high density of about 46 gÃ, Â · cm -3 , more than twice of osmium, currently the most densest element known, at 22.61 gÃ, Â · Cm -3 ; unhexquadium must be the second most dense element in the first 9 periods of the periodic table, with only its unhextrium neighbor (element 163) becoming denser (at 47 °, gÃ, Â · cm -3 ). The metallic unhexadium should be quite stable, since 8s and 8p electrons are very deeply buried in the electron nucleus and only 7d electrons are available for bonding. The metallic meta-square must have enormous cohesive energy because of its covalent bond, most likely producing a high melting point.
The theoretical interest in the chemistry of unhexquadium is largely motivated by the theoretical predictions that it, in particular the 482 isotope Uhq (with 164 protons and 318 neutrons), will be at the center of the second hypothetical stability island (the first centered around < > 306 Ubb, with 122 protons and 184 neutrons).
History
Group 12 elements have been found throughout history, used since ancient times to be found in the laboratory. The group itself has not got a trivial name, but it has been called the group IIB in the past.
Zinc
Zinc has been found used in impure forms in ancient times as well as in alloys such as brass which have been found for more than 2000 years. Zinc is clearly recognized as a metal under the appointment of Fasada in a medical lexicon thought to have originated from the Hindu king Madanapala (from the Taka dynasty) and was written around 1374. The metal was also used for alchemists. The metal name was first documented in the 16th century, and probably derived from German German for the needle-like appearance of the crystal metallic.
Isolation of metallic zinc in the West may have been achieved independently by some in the 17th century. German chemist Andreas Marggraf is usually given credit for finding pure metallic zinc in experimental 1746 by heating the calamine and charcoal mixture in a copper-covered vessel to obtain metal. Experiments on frogs by Italian physician Luigi Galvani in 1780 with brass paved the way for the invention of electric batteries, galvanizing and cathodic protection. In 1880, Galvani's friend, Alessandro Volta, discovered the Voltaic pile. The biological importance of zinc was not discovered until 1940 when carbonic anhydrase, the enzyme that rubs carbon dioxide from the blood, is shown to have zinc at its active site.
Cadmium
In 1817, cadmium was found in Germany as an impurity in zinc carbonate minerals (calamine) by Friedrich Stromeyer and Karl Samuel Leberecht Hermann. It's named after Latin cadmia for "calamine", a mixture of cadmium-bearing minerals, which in turn is named after the Greek mythological character, ?????? Cadmus, founder of Thebes. Stromeyer finally isolates cadmium metal by baking and reducing sulfides.
In 1927, the International Conference on Weight and Size redefined the meter in terms of the red cadmium spectrum line (1 m = 1.553.164.13 wavelength). This definition has changed (see krypton). At the same time, the International Prototype Meter was used as a standard for meters lengths up to 1960, when the General Conference on Weight and Size meters was defined in terms of the orange-red emission line in the electromagnetic spectrum of the 86-krypton atoms in a vacuum.
Mercury
Mercury has been found in Egyptian tombs dating back to 1500 BC, where mercury is used in cosmetics. It was also used by ancient Chinese who believed it would improve and prolong health. With 500 BC mercury is used to make amalgam (Medieval Latin amalgam, "mercury alloy") with other metals. Alchemists regard mercury as the First Material from which all metals are formed. They believe that different metals can be produced by varying the quality and quantity of sulfur contained in mercury. The purest of these is gold, and mercury is called to try to transmit base metals (or odious) into gold, which is the goal of many alchemists.
Hg is a modern chemical symbol for mercury. It comes from hydrargyrum , the Latin form of the Greek word ?????????? (hydrargyros ), which is a compound word meaning "water-silver" (hydr- = water, argyros = silver) - because it is liquid as water and shiny as silver. This element is named after the Roman god Mercury, known for its speed and mobility. This is related to planet Mercury; the astrological symbol for the planet is also one of the alchemical symbols for metal. Mercury is the only metal in which the name of the alchemical planet becomes a common name.
Copernicium
The 12 most powerful element known element, copernicium, was first created on February 9, 1996, at the Gesellschaft fÃÆ'¼r Schwerionenforschung (GSI) in Darmstadt, Germany, by Sigurd Hofmann, Victor Ninov et al. It was later officially named by the International Union of Pure and Applied Chemistry (IUPAC) after Nicolaus Copernicus on February 19, 2010, the 537th birthday of Copernicus.
Genesis
As in most other d-block groups, the abundance in the earth's crust of the 12 group elements decreases with the higher number of atoms. Zinc is the most abundant 65 parts per million (ppm) in the group while cadmium with 0.1 ppm and mercury with 0.08 ppm is an order of magnitude less abundant. Copernicium, as a synthetic element with a half-life of a few minutes, may only exist in the laboratory where it is produced.
Group 12 metals are chalcophiles, which means the elements have a low affinity for the oxide and prefer to bond with sulfides. Chalcophiles form as compacted crusts under the conditions of the Earth's initial atmospheric reduction. The most important commercial minerals of the 12 group elements are sulphide minerals. Sphalerite, which is a form of zinc sulfide, is the most heavily mined zinc ore because its concentration contains 60-62% zinc. No ore deposits contain known cadmium. Greenockite (CdS), the only important cadmium mineral, is almost always associated with sphalerite (ZnS). This relationship is due to the geochemical similarity between zinc and cadmium that makes geological separation impossible. As a result, cadmium is produced primarily as a by-product of mining, fusion, and refining of sulphide ore from zinc, and, to a lesser extent, lead and copper. One place where metal cadmium can be found is the Vilyuy River basin in Siberia. Although mercury is a very rare element in the Earth's crust, since it does not blend geochemically with the elements that make up the majority of the crust's mass, the mercury ore can be highly concentrated given the abundance of elements in ordinary rocks. The richest mercury ore contains up to 2.5% mercury in bulk, and even the thinnest concentrated deposits have at least 0.1% mercury (12,000 times the average crust abundance). These are found either as native metal (rare) or in cinnabar (HgS), corderoite, livingstonite and other minerals, with cinnabar as the most common ore.
While mercury and zinc minerals are found in considerable quantities to be mined, cadmium is too similar to zinc and is therefore always present in small quantities in the zinc ore from which it is found. The world's identified zinc resources amount to about 1.9 billion tons. Major deposits are in Australia, Canada and the United States with the largest reserves in Iran. At current consumption levels, these reserves are expected to be exhausted between 2027 and 2055. Approximately 346 million tonnes have been extracted throughout history until 2002, and one estimate found that about 109 million tonnes are still in use. In 2005, China was the top producer of mercury with nearly two-thirds of the global share followed by Kyrgyzstan. Some other countries are believed to have unrecorded mercury production from copper purification processes and with recovery from waste. Due to the high mercury toxicity, cinnabar mining and mercury purification is a toxic and hazardous cause of mercury poisoning.
Production
Zinc is the fourth most commonly used metal, only trailing iron, aluminum, and copper with an annual production of about 10 million tonnes. Worldwide, 95% of zinc is mined from sulphide ore deposits, where sphalerite (ZnS) almost always mixes with copper, lead and iron sulphides. Zinc metal is produced using extractive metallurgy. Baking converts the zinc sulfide concentrate produced during processing to zinc oxide: For further processing, two basic methods are used: pyrometallurgy or electrowinning. Pyrometallurgy treatment reduces zinc oxide by carbon or carbon monoxide at 950 ° C (1.740 ° F) into the metal, which is distilled as zinc vapor. Zinc steam is collected in a condenser. Electrowinning processing releases zinc from an ore concentrate with sulfuric acid: After this step electrolysis is used to produce zinc metal.
Cadmium is a common impurity in zinc ore, and most isolated during zinc production. Some zinc ores concentrate from zinc sulphide ore containing up to 1.4% of cadmium. Cadmium is isolated from zinc produced from stack dust by vacuum distillation when zinc is melted, or cadmium sulphate is precipitated out of the electrolysis solution.
The richest mercury ore contains up to 2.5% mercury in bulk, and even the thinnest concentrated deposits have at least 0.1% mercury, with cinnabar (HgS) being the most common ore in the sediment. Mercury is extracted by heating the cinnabar in airflow and condensing the vapor.
Super-heavy elements such as copernicium are produced by bombarding light elements in particle accelerators that induce fusion reactions. While most copernicium isotopes can be synthesized directly in this way, some heavier ones have only been observed as a result of decay of elements with higher atomic numbers. The first fusion reaction to produce copernicium was carried out by GSI in 1996, which reported detection of two copernicium-277 decay chains (though one was later recalled, since it had been based on data made by Victor Ninov):
- 208
82 Pb
70
30 Zn -> 277
112 > Cn
n
In total, about 75 copernicium atoms have been prepared using various nuclear reactions.
Apps
Because of the physical similarity they share, the group 12 elements can be found in many common situations. Zinc and cadmium are commonly used as anti-corrosion (galvanizing) agents because they will attract all local oxidation until they actually corrode. This protective coating may be applied to other metals by a hot-dip process which galvanizes a substance into a liquid form of metal, or by a passivated electroplating process by the use of a chromate salt. The Group 12 elements are also used in electrochemistry as they may act as an alternative to standard hydrogen electrodes other than as secondary reference electrodes.
In the US, zinc is used primarily for galvanizing (55%) and for brass, bronze and other alloys (37%). The relative reactivity of the zinc and its ability to attract the oxidation itself makes it an efficient sacrificial anode in cathodic protection (CP). For example, cathodic protection from buried pipes can be achieved by connecting anode made of zinc to a pipe. Zinc acts as anode (the negative end) slowly rusting as it passes an electric current to the steel pipe. Zinc is also used to protect cathodically the metals exposed to seawater from corrosion. Zinc is also used as an anode material for batteries such as zinc-carbon batteries or battery cells/zinc-air fuel cells. A widely used alloy containing zinc is brass, in which copper is mixed with anywhere from 3% to 45% zinc, depending on the type of brass. Brass is generally more brittle and stronger than copper and has superior corrosion resistance. These properties make it useful in communication equipment, hardware, musical instruments, and water valves. Other widely used alloys containing zinc include nickel silver, metal typewriter, soft solder and aluminum, and commercial bronze. Zinc alloys especially with small amounts of copper, aluminum, and magnesium are useful in die casting as well as spin casting, especially in the automotive, electrical, and hardware industries. These alloys are marketed under the name Zamak. Approximately one quarter of all zinc output, in the United States (2009), is consumed in the form of zinc compounds, various of which are used industrially.
Cadmium has many common industrial uses as it is a key component in battery production, present in cadmium pigments, coatings, and generally used in electroplating. In 2009, 86% cadmium was used in batteries, especially on rechargeable nickel-cadmium batteries. The European Union banned the use of cadmium in electronics in 2004 with some exceptions but reduced the allowable content of cadmium in electronics to 0.002%. Electroplating cadmium, consuming 6% of global production, can be found in the aircraft industry because of its ability to resist corrosion when applied to steel components.
Mercury is used primarily for the manufacture of industrial chemicals or for electrical and electronic applications. These are used in some thermometers, especially those used to measure high temperatures. The ever-increasing amount is used as mercury gas in fluorescent lamps, while most other applications are gradually removed due to health and safety regulations, and in some applications replaced with less toxic but much more expensive Galinstan alloys. Mercury and its compounds have been used in medicine, although they are much less common today than ever, now the effects of mercury poison and its compounds are more widely understood. It is still used as an ingredient in dental amalgam. By the end of the 20th century the greatest use of mercury was in the process of mercury cells (also called the Castner-Kellner process) in the production of chlorine and caustic soda.
Biological and toxicity roles
Group 12 elements have some effects on biological organisms because cadmium and mercury are toxic while zinc is required by most plants and animals in small quantities.
Zinc is an important trace element, which is necessary for plants, animals, and microorganisms. This is "usually the second most transition metal in organism" after iron and it is the only metal that appears in all classes of enzymes. There are 2-4 grams of zinc that is distributed throughout the human body, and it plays "a biological role everywhere". A 2006 study estimated that about 10% of human protein (2800) could potentially bind zinc, in addition to the hundreds that transport and increase zinc traffic. In the US, Recommended Dietary Allowance (RDA) is 8 mg/day for women and 11 mg/day for men. Harmful excess supplements may be a problem and may not exceed 20 mg/day in healthy people, although the US National Research Council sets a tolerable upper intake of 40 mg/day.
Mercury and cadmium are toxic and can cause environmental damage if they enter a river or rainwater. This can lead to contaminated crops as well as bioaccumulation of mercury in the food chain causing an increase in diseases caused by mercury and cadmium poisoning.
Note
References
Bibliography
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