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halogen(hăl`əjĕn) [Gr.,=salt-bearing], any of the chemically active elements found in Group 17 of the periodic tableperiodic table,
chart of the elements arranged according to the periodic law discovered by Dmitri I. Mendeleev and revised by Henry G. J. Moseley. In the periodic table the elements are arranged in columns and rows according to increasing atomic number (see the table entitled
..... Click the link for more information. ; the name applies especially to fluorinefluorine
, gaseous chemical element; symbol F; at. no. 9; at. wt. 18.9984; m.p. −219.6°C;; b.p. −188.14°C;; density 1.696 grams per liter at STP; valence −1. Fluorine is a yellowish, poisonous, highly corrosive gas.
..... Click the link for more information. (symbol F), chlorinechlorine
[Gr.,=green], gaseous chemical element; symbol Cl; at. no. 17; interval in which at. wt. ranges 35.446–35.457; m.p. −100.98°C;; b.p. −34.6°C;; density 3.2 grams per liter at STP; valence −1, +1, +3, +5, +7.
..... Click the link for more information. (Cl), brominebromine
[Gr.,=stench], volatile, liquid chemical element; symbol Br; at. no. 35; at. wt. 79.904; m.p. –7.2°C;; b.p. 58.78°C;; sp. gr. of liquid 3.12 at 20°C;; density of vapor 7.14 grams per liter at STP; valence −1, +1, +3, +5, or +7.
..... Click the link for more information. (Br), and iodineiodine
[Gr.,=violet], nonmetallic chemical element; symbol I; at. no. 53; at. wt. 126.90447; m.p. 113.5°C;; b.p. 184.35°C;; sp. gr. 4.93 at 20°C;; valence −1, +1, +3, +5, or +7.
..... Click the link for more information. (I). Astatineastatine
[Gr.,=unstable], semimetallic radioactive chemical element; symbol At; at. no. 85; at. wt. of most stable isotope 210; m.p. 302°C; (estimated); b.p. 337°C; (estimated); density unknown; valence believed to be +1, +3, +5, or +7.
..... Click the link for more information. (At), formerly known as alabamine, is a radioactive element also classed as a halogen; its most stable isotope (which does not occur in nature) has a half-life of less than 8 1-2 hr. The chemical and physical properties of astatine are not well known; it is believed to resemble iodine. The halogens are the best-defined family of chemical elements. Chemically they closely resemble one another; they are nonmetallic and form monovalent negative ions. They also exhibit an almost perfect gradation of physical properties. Fluorine, a pale yellow gas, is the least dense and chemically the most active, displacing the other halogens from their compounds and even displacing oxygen from water. Chlorine, a yellow-green gas, is more dense and less reactive than fluorine. Bromine is a dark red liquid. Iodine is a grayish black solid and is the least chemically active of the four; however, among the nonmetals only oxygen is more reactive than iodine. Pure halogens exist as diatomic molecules, e.g., Cl2; they form interhalogen compounds, i.e., compounds between two halogens. The halogens form numerous compounds with other elements. With hydrogen they form hydrogen halides, whose water solutions are called hydrohalic acids, e.g., the water solution of hydrogen chloridehydrogen chloride,
chemical compound, HCl, a colorless, poisonous gas with an unpleasant, acrid odor. It is very soluble in water and readily soluble in alcohol and ether. It fumes in moist air. It is not flammable, and the liquid is a poor conductor of electricity.
..... Click the link for more information. is called hydrochloric acid. They form numerous metal halides, or saltssalt,
chemical compound (other than water) formed by a chemical reaction between an acid and a base (see acids and bases). Characteristics and Classification of Salts
The most familiar salt is sodium chloride, the principal component of common table salt.
..... Click the link for more information. , e.g., sodium chloride, common table salt. They also form halocarbons, compounds with carbon and often other elements such as hydrogen and oxygen. Chloroformchloroform
, CHCl3, volatile, colorless, nonflammable liquid that has a sweetish taste and a somewhat pungent odor; it boils at 61.7°C;. It dissolves freely in ethanol and ether but does not mix with water.
..... Click the link for more information. , iodoformiodoform
, CHI3, yellow crystalline solid that has a penetrating odor. It melts at 119°C; and is insoluble in water but soluble in ether or ethanol. Iodoform was formerly used as an antiseptic.
..... Click the link for more information. , and carbon tetrachloridecarbon tetrachloride
, CCl4, colorless, poisonous, liquid organic compound that boils at 76.8°C;. It is toxic when absorbed through the skin or when inhaled. It reacts at high temperatures to form the poisonous gas phosgene.
..... Click the link for more information. are halocarbons. Some other halogen compounds are calomel (mercurous chloride), fluoritefluorite
, mineral appearing in various colors, e.g., green, yellow-brown, rose, and red. Chemically, it is calcium fluoride, CaF2. Its crystals, commonly cubic, are transparent or translucent and under certain conditions exhibit fluorescence.
..... Click the link for more information. , sal ammoniac (ammonium chlorideammonium chloride
, chemical compound, NH4Cl, a white or colorless, odorless, water-soluble, cubic crystalline salt with a biting taste, commonly known as sal ammoniac.
..... Click the link for more information. ), corrosive sublimate (mercuric chloridemercuric chloride
or mercury (II) chloride,
chemical compound, HgCl2, a white powder of colorless rhombohedral crystals, somewhat soluble in water. It is also called bichloride of mercury or corrosive sublimate. It is extremely poisonous.
..... Click the link for more information. ), and chlorine bleaches.
A type of incandescent lamp with a higher energy efficiency than standard ones.
Any of the elements of the halogen family, consisting of fluorine, chlorine, bromine, iodine, and astatine.
any of the chemical elements fluorine, chlorine, bromine, iodine, and astatine. They are all monovalent and readily form negative ions