Pnictogen
Template:Periodic table (group 15)
The nitrogen group (also known as the pnictogens)[1] is a periodic table group consisting of nitrogen (N), phosphorus (P), arsenic (As), antimony (Sb), bismuth (Bi) and ununpentium (Uup) (unconfirmed).
In modern IUPAC notation, it is called Group 15. In the old IUPAC and CAS systems, it was called Group VB and Group VA, respectively (pronounced "group five B" and "group five A", "V" for the Roman numeral 5).[2] In the field of semiconductor physics, it is still universally called Group V.[3] The "five" ("V") in the historical names comes from the "pentavalency" of nitrogen, reflected by the stoichiometry of compounds such as N2O5.
Characteristics
Chemical
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 |
|---|---|---|
| 7 | nitrogen | 2, 5 |
| 15 | phosphorus | 2, 8, 5 |
| 33 | arsenic | 2, 8, 18, 5 |
| 51 | antimony | 2, 8, 18, 18, 5 |
| 83 | bismuth | 2, 8, 18, 32, 18, 5 |
This group has the defining characteristic that all the component elements have 5 electrons in their outermost shell, that is 2 electrons in the s subshell and 3 unpaired electrons in the p subshell. They are therefore 3 electrons short of filling their outermost electron shell in their non-ionized state. The most important elements of this group are nitrogen (N), which in its diatomic form is the principal component of air, and phosphorus (P), which, like nitrogen, is essential to all known forms of life.
Compounds
Binary compounds of the group can be referred to collectively as pnictides. The spelling derives from the Greek verb πνίγειν (pnígein), to "choke" or "stifle", which is a property of molecular nitrogen in the absence of oxygen; it can also be used as a mnemonic for the two most common members, P and N. The name pentels (from Greek πέντε, pénte, five) was also used for this group at one time,[4] stemming from the earlier group naming convention (Group VB).
These elements are also noted for their stability in compounds due to their tendency for forming double and triple covalent bonds. This is the property of these elements which leads to their potential toxicity, most evident in phosphorus, arsenic and antimony. When these substances react with various chemicals of the body, they create strong free radicals not easily processed by the liver, where they accumulate. Paradoxically it is this strong bonding which causes nitrogen and bismuth's reduced toxicity (when in molecules), as these form strong bonds with other atoms which are difficult to split, creating very unreactive molecules. For example N2, the diatomic form of nitrogen, is used as an inert gas in situations where using argon or another noble gas would be too expensive.
Physical
The nitrogen group consists of two non-metals, two metalloids, one metal, and one synthetic (presumably metallic) element. All the elements in the group are a solid at room temperature except for nitrogen which is a gas at room temperature.
Nitrogen and bismuth, despite both being part of the nitrogen group, are very different in their physical properties. For example, at STP nitrogen is a transparent nonmetallic gas, while bismuth is a brittle pinkish metallic solid.
History and etymology
The term "pnictogen" was suggested by the Dutch chemist Anton Eduard van Arkel in the early 1950s. It is also spelled "pnicogen" or "pnigogen". It comes from the Greek root pnikta ("suffocated things"), and thus the word "pnictogen" is also a reference to the German name for nitrogen (Stickstoff, "suffocating substance"). Hence, "pnictogen" could be translated as "suffocator maker". The word "pnictide" also comes from the same root.[5]
Biological role and toxicity
The lighter members of Group 15, nitrogen and phosphorus, are present in all living organisms. Nitrogen's most important role is as a constituent of the class of biological molecules known as proteins. Phosphorus most commonly occurs as phosphates, including in mineral form in bones, and in molecules involved in metabolism such as ATP. The heavier members of the group do not appear to have any biological role.
Arsenic and antimony are generally toxic to organisms, although bismuth much less so. This is at variance with Groups 12, 13, and 14, where the most toxic elements are the heaviest in their respective groups.
See also
- Oxypnictide, including superconductors discovered in 2008.
- Ferropnictide, including oxypnictide superconductors.
Notes
- ^ Edited by N G Connelly and T Damhus (with R M Hartshorn and A T Hutton), ed. (2005). Nomenclature of Inorganic Chemistry: IUPAC Recommendations 2005 section IR-3.5 (PDF). ISBN 0-85404-438-8.
{{cite book}}:|editor=has generic name (help) - ^ Fluck, E. New notations in the periodic table. Pure & App. Chem. 1988, 60, 431–436.[1]
- ^ For example, a 2005 book is titled Properties of group-IV, III-V and II-VI semiconductors.
- ^ Holleman, Arnold Frederik; Wiberg, Egon (2001), Wiberg, Nils (ed.), Inorganic Chemistry, translated by Eagleson, Mary; Brewer, William, San Diego/Berlin: Academic Press/De Gruyter, p. 586, ISBN 0-12-352651-5
- ^ Girolami, Gregory S. (2009). "Origin of the Terms Pnictogen and Pnictide". Journal of Chemical Education. 86 (10). American Chemical Society: 1200. Bibcode:2009JChEd..86.1200G. doi:10.1021/ed086p1200. Retrieved February 6, 2012.
| bgcolor="Template:Element color/Nonmetals" | Nonmetals | bgcolor="Template:Element color/Metalloids" | Metalloids | bgcolor="Template:Element color/Poor metals" | Poor metals | atomic number in Template:Element color/Gas are gases | atomic number in Template:Element color/Solid are solids | style="border:Template:Element frame/Primordial;" | solid borders are primordial elements (older than the Earth) | style="border:Template:Element frame/Synthetic;" | dotted borders are radioactive, synthetic elements |
|---|
