Halogen
A halogen is an element from group 17 of the periodic table, that is, one of fluorine, chlorine, bromine, iodine or astatine.[1] The name is derived from the Ancient Greek ἅλς (hals, genitive ἁλός halos, "salt") and -γενής (genēs, "producer of"), and was first used in 1811 by the German chemist J. S. C. Schweigger (1779–1857) to refer to chlorine, the only element that was known at that time to react directly with metals to produce salts.[Note 1][3]
Elements
All of the halogens are non-metals. Fluorine and chlorine are gases at room temperature, while bromine is a volatile liquid and iodine a volatile solid. None of the halogens occurs naturally in the elemental state: compounds of fluorine and chlorine are very abundant in the Earth's crust, while bromine and iodine are less so, with commercial deposits being very rare. Virtually nothing is known of the bulk properties of astatine, which has no stable isotopes and is possibly the rarest of the naturally occuring elements.
| F | Cl | Br | I | At | ||
|---|---|---|---|---|---|---|
| Atomic weight | 18.998 4032(5) | 35.453(2) | 79.904(1) | 126.904 47(3) | — | |
| Melting point/°C | −218.6 | −101.0 | −7.25 | 113.6 | ||
| Boiling point/°C | −188.1 | −34.0 | 59.5 | 185.2 |
Notes and references
Notes
- ↑ It is often stated that the term "halogen" was coined by Swedish chemist Jöns Jacob Berzelius (1779–1848): this misconception seems to arise from the first English use of the word, which was in a translation of one of Berzelius' papers in the Proceedings of the American Philosophical Society (1832, 2, 219).[2]
References
- ↑ Nomenclature of Inorganic Chemistry; IUPAC Recommendations 2005; Royal Society of Chemistry: Cambridge, 2005; pp 51–52. ISBN 0-85404-438-8, <http://www.iupac.org/publications/books/rbook/Red_Book_2005.pdf>.
- ↑ Halogen. In A New English Dictionary on Historical Principles; Oxford University Press, 1901; Vol. 5, p 44.
- ↑ Greenwood, Norman N.; Earnshaw, A. Chemistry of the Elements; Pergamon: Oxford, 1984; pp 920–21. ISBN 0-08-022057-6.
External links
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