Group 12 element

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Group → 12
↓ Period
4 Zinc, fragment and sublimed 99,995%
30
Zn
5 Cadmium, crystal bar 99,99%
48
Cd
6 Mercury, liquid
80
Hg
7 112
Cn
Legend
Transition metal
Primordial element
Synthetic

A group 12 element is one of the elements in group 12 (IUPAC style) in the periodic table. This includes zinc (Zn), cadmium (Cd) and mercury (Hg).[1][2][3] The further inclusion of copernicium (Cn) in group 12 is supported by recent experiments on individual copernicium atoms.[4] Although this group lies in the d-block of the periodic table it is not always considered to be a part of the transition metals as the elements in this group have a filled d-subshell. The group itself has not acquired a trivial name.

The three Group 12 elements that occur naturally are zinc, cadmium and mercury. The first two members of the group share similar properties as they are solid metals under standard conditions. Mercury is the only metal that is a liquid at room temperature. As copernicium does not occur in a natural, stable form in nature, it has to be synthesized in the laboratory; none of its isotopes have been found occurring in nature. So far, no experiments in a supercollider were conducted to synthesize the next member of the group, either unhexbium (Uhb) or unhexquadium (Uhq), and it is unlikely that they will be synthesized in the near future.

Contents

[edit] Characteristics

[edit] Chemistry

Like other groups, the members of this family show patterns in its electron configuration, especially the outermost shells resulting in trends in chemical behavior:

Z Element No. of electrons/shell
30 zinc 2, 8, 18, 2
48 cadmium 2, 8, 18, 18, 2
80 mercury 2, 8, 18, 32, 18, 2
112 copernicium 2, 8, 18, 32, 32, 18, 2

Most of the chemistry has been observed only for the first three members of the group. The chemistry of copernicium is not very established and therefore the rest of the section deals only with zinc, cadmium and mercury.

All elements in this group are metals. The similarity of the metallic radii of cadmium and mercury is an effect of the lanthanide contraction. So, the trend in this group is unlike the trend in group 2, the alkaline earths, where metallic radius increases smoothly from top to bottom of the group. All three metals have relatively low melting and boiling points, indicating that the metallic bond is relatively weak, with relatively little overlap between the valence band and the conduction band.[5] Thus, zinc is close to the boundary between metallic and metalloid elements, which is usually placed between gallium and germanium, though gallium participates in semi-conductors such as gallium arsenide.

H   He
Li Be   B C N O F Ne
Na Mg   Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
Cs Ba * Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
Fr Ra ** Rf Db Sg Bh Hs Mt Ds Rg Cn Uut Uuq Uup Uuh Uus Uuo
 
  * La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
  ** Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr
Group 12 in the periodic table

Zinc and cadmium are the electropositive elements in the group while mercury is not.[5] As a result, zinc metal and cadmium are good reducing agents. The elements of group group 12 have an oxidation state of +2 in which the ions have the rather stable d10 electronic configuration, with a full sub-shell. However, mercury can easily be reduced to the +1 oxidation state; usually, as in the ion Hg22+, two mercury(I) ions come together to form a metal-metal bond and a diamagnetic species.[6] Cadmium can also form species such as [Cd2Cl6]4− in which the metal's oxidation state is +1. Just as with mercury, the formation of a metal-metal bond results in a diamagnetic compound in which there are no unpaired electrons; thus, making the species very reactive. Zinc(I) is known only in the gas phase, in such compounds as linear Zn2Cl2, analogous to calomel.

All three metal ions form many tetrahedral species, such as MCl42−. When a divalent ion of these elements forms a tetrahedral complex, it obeys the octet rule. Both zinc and cadmium can also form octahedral complexes such as the aqua ions [M(H2O)6]2+ which are present in aqueous solutions of salts of these metals.[7] Covalent character is achieved by using the 4d or 5d orbitals, respectively, forming sp3d2 hybrid orbitals. Mercury, however, rarely exceeds a coordination number of four; when it does so the 5f orbitals must be involved. Coordination numbers of 2, 3, 5, 7 and 8 are also known.

The elements in group 12 are usually considered to be d-block elements, but not transition elements as the d-shell is full. Some authors classify these elements as main-group elements because the valence electrons are in ns2 orbitals. Nevertheless, zinc shares many characteristics with the neighboring transition metal, copper. For instance, zinc complexes merit inclusion in the Irving-Williams series as zinc forms many complexes with the same stoichiometry as complexes of copper(II), albeit with smaller stability constants.[8] There is little similarity between cadmium and silver as compounds of silver(II) are rare and those that do exist are very strong oxidizing agents. Likewise the common oxidation state for gold is +3, which precludes there being much common chemistry between mercury and gold, though there are similarities between mercury(I) and gold(I) such as the formation of linear dicyano complexes, [M(CN)2]−.

[edit] Physical

The table below is a summary of the key physical properties of the group 12 elements.

Properties of the Group 12 elements
Name Zinc Cadmium Mercury Copernicium
Melting point 693 K (420 °C) 594 K (321 °C) 234 K (−39 °C)  ?
Boiling point 1180 K (907 °C) 1040 K (767 °C) 630 K (357 °C)  ?
Density 7.14 g·cm−3 8.65 g·cm−3 13.534 g·cm−3  ?
Appearance silver-gray silvery bluish-gray metallic silvery  ?
Atomic radius 135 pm 155 pm 150 pm  ?

[edit] History

The elements of group 12 have been found throughout history, being used since ancient times to being discovered in laboratories.

[edit] Zinc

In ancient times zinc has been found being used in impure forms as well as in alloys that have been found to be over 2000 years old.[9]

[edit] Cadmium

In 1817 Cadmium was discovered in Germany as an impurity in zinc carbonate by Friedrich Stromeyer and Karl Samuel Leberecht Hermann.[10]

[edit] Mercury

Mercury has been found in Egyptian tombs which have been dated back to 1500 BC,[11] where mercury was used in cosmetics. It was also used by the ancient Chinese who believed it would improve and prolong health.[12]

[edit] Copernicium

The heaviest known group 12 element, copernicium was first created on February 9, 1996, at the Gesellschaft für Schwerionenforschung (GSI) located in Darmstadt, Germany by Sigurd Hofmann, Victor Ninov et al.[13] It was then officially named on February 19, 2010 by the International Union of Pure and Applied Chemistry.[14]

[edit] Eka-copernicium

The next element below copernicium is expected to be either the 162th element (unhexbium, Uhb) or the 164th element (unhexquadium, Uhq). There are no plans to attempt to synthesize either of these in the near future, since they are both late period 8 elements. Currently none of the period 8 elements have been discovered yet, and it is possible that due to drip instabilities, only the lower period 8 elements are physically possible.[15]

[edit] Occurrence

Like in most other d-block groups the abundance in Earth's crust decreases with higher atomic number, and so the zinc is with 65 parts per million (ppm) the most abundant in the group while cadmium with 0.1 ppm and mercury with 0.040 ppm are orders of magnitude less abundant.[16] Copernicium, as a synthetic element with a half-life of a few minutes, may only be present in the laboratories where it was produced.

The commercially most important minerals of group 12 elements are sulfide minerals, for example sphalerite (ZnS), greenockite (CdS) and cinnabar (HgS).[5] While mercury and zinc minerals are found in large enough quantities to be mined, cadmium is too similar to zinc and therefore is always present in small quantities in zinc ores.

[edit] Production

Zinc is the fourth most common metal in use, trailing only iron, aluminium, and copper with an annual production of about 10 million tonnes.[17] Worldwide, 95% of the zinc is mined from sulfidic ore deposits, in which sphalerite (ZnS) is nearly always mixed with the sulfides of copper, lead and iron. Zinc metal is produced using extractive metallurgy.[18] Roasting converts the zinc sulfide concentrate produced during processing to zinc oxide:[19] For further processing two basic methods are used: pyrometallurgy or electrowinning. Pyrometallurgy processing reduces zinc oxide with carbon or carbon monoxide at 950 °C (1,740 °F) into the metal, which is distilled as zinc vapor.[20] The zinc vapor is collected in a condenser.[19] Electrowinning processing leaches zinc from the ore concentrate by sulfuric acid:[21] After this step electrolysis is used to produce zinc metal.[19]

Cadmium is a common impurity in zinc ores, and it is most isolated during the production of zinc. Some zinc ores concentrates from sulfidic zinc ores contain up to 1.4% of cadmium.[22] Cadmium is isolated from the zinc produced from the flue dust by vacuum distillation if the zinc is smelted, or cadmium sulfate is precipitated out of the electrolysis solution.[23]

The richest mercury ores contain up to 2.5% mercury by mass, and even the leanest concentrated deposits are at least 0.1% mercury, with cinnabar (HgS) being the most common ore in the deposits.[24] Mercury is extracted by heating cinnabar in a current of air and condensing the vapor.[25]

Super-heavy elements such as copernicium are produced by bombarding lighter elements in particle accelerators that induces fusion reactions. Whereas most of the isotopes of rutherfordium can be synthesized directly this way, some heavier ones have only been observed as decay products of elements with higher atomic numbers.[26] The first fusion reaction to produce copernicium was performed by GSI in 1996, who reported the detection of two decay chains of copernicium-277.[13]

208
82Pb + 70
30Zn → 277
112Cn + n

In total, approximately 75 atoms of copernicium have been prepared using various nuclear reactions.

[edit] Applications

Due to the physical similarities which they share, the group 12 elements can be found in many common situations. Zinc and cadmium are commonly used as anti-corrosion agents[1] as they will attract all local oxidation until they completely corrode.[27] These protective coatings can be applied to other metals through by hot-dip galvanizing a substance into the molten form of the metal,[28] or through the process of electroplating which may be passivated by the use of chromate salts.[29]

Group 12 elements are also used in electrochemistry as they may act as an alternative to the standard hydrogen electrode in addition to being a secondary reference electrode.[30] Zinc is commonly used as and anode in batteries and fuel cells;[31] whereas, cadmium is commonly used in recharable nickel-cadmium batteries.[32]

[edit] Biological role

The group 12 elements have multiple effects on biological organisms as cadmium and mercury are toxic while zinc is required by most plants and animals in trace amounts. Zinc is required by most organisms in trace amounts as it is present in enzymes where it is often present as a catalytic agent for enzyme-directed reactions.[33] In large amounts zinc may be toxic to biological organisms as it prevents cells from absorbing copper and iron.[34]

Mercury and cadmium are toxic and may cause environmental damage if they enter rivers or rain water. This may result in contaminated crops[35] as well as the bioaccumulation of mercury in a food chain leading to an increase in illnesses caused by mercury and cadmium poisoning.[36]

Copernicium has no biological role[37] and does not occur in nature,[38] but it is most likely to be toxic due to its radioactivity.[39][40]

[edit] References

  1. ^ a b Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Oxford: Butterworth-Heinemann. ISBN 0080379419. 
  2. ^ Cotton, F. Albert; Wilkinson, Geoffrey; Murillo, Carlos A.; Bochmann, Manfred (1999), Advanced Inorganic Chemistry (6th ed.), New York: Wiley-Interscience, ISBN 0-471-19957-5 
  3. ^ Housecroft, C. E.; Sharpe, A. G. (2008). Inorganic Chemistry (3rd ed.). Prentice Hall. ISBN 978-0131755536. 
  4. ^ Eichler, R; Aksenov, NV; Belozerov, AV; Bozhikov, GA; Chepigin, VI; Dmitriev, SN; Dressler, R; Gäggeler, HW et al (2007). "Chemical Characterization of Element 112". Nature 447 (7140): 72–75. Bibcode 2007Natur.447...72E. doi:10.1038/nature05761. PMID 17476264. 
  5. ^ a b c Moss, Alex (2003). "Descriptive P-block Notes". Alchemyst Online. http://www.alchemyst.co.uk/alchemystry/pdf/Inorganic/descriptive_pblock.pdf. Retrieved June 2, 2011. 
  6. ^ Lindberg, S.E.; Stratton, W.J. (1998). "Atmospheric Mercury Speciation: Concentrations and Behavior of Reactive Gaseous Mercury in Ambient Air". Environmental Science and Technology (American Chemical Society) 32 (1): 49–57. doi:10.1021/es970546u. 
  7. ^ Richens, David T. (September 1997). The Chemistry of Aqua Ions. J. Wiley. ISBN 0-4719-7058-1. 
  8. ^ Al-Niaimi, N.S.; Hamid, H.A. (1976). "Stabilities of nickel(II), copper(II), zinc(II) and dioxouranium(II) complexes of some β-diketones". Journal of Inorganic and Nuclear Chemistry (Elsevier Ltd.) 3 (5): 849–852. doi:10.1016/0022-1902(77)80167-X. 
  9. ^ Weeks, Mary Elvira (1933). III. Some Eighteenth-Century Metals. Easton, PA: Journal of Chemical Education. p. 20. ISBN 0766138720. 
  10. ^ "Cadmium". Kirk-Othmer Encyclopedia of Chemical Technology. 5 (4-th ed.). New York: John Wiley & Sons. 1994. 
  11. ^ "Mercury and the environment — Basic facts". Environment Canada, Federal Government of Canada. 2004. http://www.ec.gc.ca/MERCURY/EN/bf.cfm. Retrieved 2008-03-27. 
  12. ^ Wright, David Curtis (2001). The History of China. Greenwood Publishing Group. p. 49. ISBN 031330940X. 
  13. ^ a b S. Hofmann, et al. (1996). "The new element 112". Zeitschrift für Physik A 354 (1): 229–230. doi:10.1007/BF02769517. 
  14. ^ Barber, Robert C.; Gäggeler, Heinz W.; Karol, Paul J.; Nakahara, Hiromichi; Vardaci, Emanuele; Vogt, Erich. "[IUPAC]Element 112 is Named Copernicium". Pure and Applied Chemistry (iupac.org) 81 (7): 1331. doi:10.1351/PAC-REP-08-03-05. http://www.iupac.org/web/nt/2010-02-20_112_Copernicium. Retrieved 2010-02-22. 
  15. ^ "Extended elements: new periodic table". Rsc.org. http://www.rsc.org/Publishing/ChemScience/Volume/2010/11/Extended_elements.asp. Retrieved 2011-03-06. 
  16. ^ Wedepohl, K. Hans (1995). "The composition of the continental crust". Geochimica et Cosmochimica Acta 59 (7): 1217–1232. Bibcode 1995GeCoA..59.1217W. doi:10.1016/0016-7037(95)00038-2. 
  17. ^ "Zinc: World Mine Production (zinc content of concentrate) by Country". 2006 Minerals Yearbook: Zinc (Washington, D.C.: United States Geological Survey): Table 15. February 2008. http://minerals.usgs.gov/minerals/pubs/commodity/zinc/myb1-2006-zinc.pdf. Retrieved 2009-01-19. 
  18. ^ Rosenqvist, Terkel (1922). Principles of Extractive Metallurgy (2 ed.). Tapir Academic Press. pp. 7, 16, 186. ISBN 8251919223. 
  19. ^ a b c Porter, Frank C. (1991). Zinc Handbook. CRC Press. ISBN 9780824783402. http://books.google.com/?id=laACw9i0D_wC. 
  20. ^ Bodsworth, Colin (1994). The Extraction and Refining of Metals. CRC Press. p. 148. ISBN 0849344336. 
  21. ^ Gupta, C. K.; Mukherjee, T. K. (1990). Hydrometallurgy in Extraction Processes. CRC Press. p. 62. ISBN 0849368049. 
  22. ^ National Research Council (U.S.), Panel on Cadmium, Committee on Technical Aspects of Critical and Strategic Material (1969). Trends in Usage of Cadmium: Report. National Research Council, National Academy of Sciences-National Academy of Engineering. pp. 1–3. http://books.google.com/?id=okArAAAAYAAJ. 
  23. ^ Scoullos, Michael J (2001-12-31). Mercury, cadmium, lead: handbook for sustainable heavy metals policy and regulation. pp. 104–116. ISBN 9781402002243. http://books.google.de/books?id=9yzN-QGag_8C&pg=PA104. 
  24. ^ Rytuba, James J. (2003). "Mercury from mineral deposits and potential environmental impact". Environmental Geology 43 (3): 326–338. doi:10.1007/s00254-002-0629-5. 
  25. ^ Vallero, Daniel A (2008). Fundamentals of air pollution. pp. 865–866. ISBN 9780123736154. http://books.google.com/books?id=4AV2Wds_NZAC&pg=PA865. 
  26. ^ Barber, Robert C.; Gäggeler, Heinz W.; Karol, Paul J.; Nakahara, Hiromichi; Vardaci, Emanuele; Vogt, Erich (2009). "Discovery of the element with atomic number 112 (IUPAC Technical Report)". Pure and Applied Chemistry 81 (7): 1331. doi:10.1351/PAC-REP-08-03-05. 
  27. ^ Stwertka, Albert (1998). "Zinc". Guide to the Elements (Revised ed.). Oxford University Press. ISBN 0-19-508083-1. 
  28. ^ Emsley, John (2001). "Zinc". Nature's Building Blocks: An A-Z Guide to the Elements. Oxford, England, UK: Oxford University Press. pp. 499–505. ISBN 0-19-850340-7. http://books.google.com/?id=j-Xu07p3cKwC. 
  29. ^ Smith C.J.E., Higgs M.S., Baldwin K.R. (April 20, 1999). "Advances to Protective Coatings and their Application to Ageing Aircraft". RTO MP-25. http://ftp.rta.nato.int/public//PubFulltext/RTO/MP/RTO-MP-025///MP-025-15.pdf. Retrieved May 29, 2011. 
  30. ^ Newman, John (2004). Electrochemical Systems. New Jersey: John Wiley & Sons. ISBN 0471477567. 
  31. ^ Besenhard, Jürgen O. (1999). Handbook of Battery Materials. Wiley-VCH. ISBN 3527294694. http://www.ulb.tu-darmstadt.de/tocs/60178752.pdf. Retrieved 2008-10-08. 
  32. ^ "Battery collection; recycling, nature protected". European Union. http://www.europarl.europa.eu/sides/getDoc.do?pubRef=-//EP//TEXT+IM-PRESS+20060628BRI09328+FULL-TEXT+DOC+XML+V0//EN. Retrieved November 4, 2008. 
  33. ^ Stipanuk, Martha H. (2006). Biochemical, Physiological & Molecular Aspects of Human Nutrition. W. B. Saunders Company. pp. 1043–1067. ISBN 9780721644523. 
  34. ^ Fosmire, G. J. (1990). "Zinc toxicity". American Journal of Clinical Nutrition 51 (2): 225–7. PMID 2407097. 
  35. ^ Nogawa, Koji; Kobayashi, E; Okubo, Y; Suwazono, Y (2004). "Environmental cadmium exposure, adverse effects, and preventative measures in Japan". Biometals 17 (5): 581–587. doi:10.1023/B:BIOM.0000045742.81440.9c. PMID 15688869. http://www.springerlink.com/content/n0773057mw738u05/. 
  36. ^ Mozaffarian D, Rimm EB (2006). "Fish intake, contaminants, and human health: evaluating the risks and the benefits". JAMA 296 (15): 1885–99. doi:10.1001/jama.296.15.1885. PMID 17047219. http://jama.ama-assn.org/cgi/content/full/296/15/1885. 
  37. ^ Winter, Mark. "WebElements Periodic Table of the Elements | Copernicium | biological information". WebElements. http://www.webelements.com/copernicium/biology.html. Retrieved 9 January 2012. 
  38. ^ Winter, Mark. "WebElements Periodic Table of the Elements | Copernicium | geological information". WebElements. http://www.webelements.com/copernicium/geology.html. Retrieved 9 January 2012. 
  39. ^ Donnelly EH, Nemhauser JB, Smith JM, et al. (2010). "Acute radiation syndrome: assessment and management". South. Med. J. 103 (6): 541–6. doi:10.1097/SMJ.0b013e3181ddd571. PMID 20710137. 
  40. ^ Xiao M, Whitnall MH (2009). "Pharmacological countermeasures for the acute radiation syndrome". Curr Mol Pharmacol 2 (1): 122–33. doi:10.2174/1874467210902010122. PMID 20021452. 
Layouts
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Group 12 elements
   

Zinc
Zn
Atomic Number: 30
Atomic Weight: 65.38
Melting Point: 692.88 K
Boiling Point: 1180 K
Specific mass: 7.134 g/cm3
Electronegativity: 1.65

Cadmium
Cd
Atomic Number: 48
Atomic Weight: 112.411
Melting Point: 594.33 K
Boiling Point: 1040 K
Specific mass: 8.69 g/cm3
Electronegativity: 1.69

Mercury
Hg
Atomic Number: 80
Atomic Weight: 200.59
Melting Point: 234.43 K
Boiling Point: 630 K
Specific mass: 13.5336 g/cm3
Electronegativity: 2

Copernicium
Cn
Atomic Number: 112
Atomic Weight: [285]
Melting Point: ? K
Boiling Point: ? K
Specific mass: ? g/cm3
Electronegativity: ?
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