Halogens

HALOGENS, haloids (from Greek hals—salt, eidos—form, gennao—I produce), the name of a group of chemical elements that easily form salts by direct combination with metals. These include the following elements: fluorine (F), chlorine (Cl), bromine (Br), and iodine (J). In Mendeleev's periodic table, they all occupy the same group—the seventh—since they are heptavalent at their maximum. Due to their great affinity for other elements, halogens do not occur in nature in a free state; however, their compounds with metals (sodium, potassium, magnesium) are very widespread and are almost always found together, though not in equal quantities. Halogens are constituents of animal body substances. Free halogens, with the exception of fluorine, can be obtained by the electrolysis of a halide salt or by the action of sulfuric acid on a halogen salt in the presence of manganese dioxide. Fluorine, although obtained in this way, reacts again immediately. The physical and chemical properties of both the halogens themselves and their compounds are very similar to each other and change sequentially with changes in atomic weight. As can be seen from the accompanying table, with an increase in atomic weight, matter becomes denser, the difficulty of transition from one state to another increases, and the coloration of the elements becomes more intense. Fluorine is a light yellow-green gas, chlorine is a yellow-green gas, bromine is a reddish-brown easily evaporating liquid, and iodine is a crystalline solid that gives off violet vapors upon heating. Specific gravity of halogens: Atomic weight, Boiling point, Melting point. Fluorine: 19.00, -187°, -222°. Chlorine: 35.48, -33.7°, -102°, 1.11 (liquid at 0°). Bromine: 79.92, +58.7°, -7.3°, 2.49 (liquid at 0°). Iodine: 126.92, +184.4°, +113°, 3.102 (liquid at 25°), 4.95 (solid at 17°). Chemically, halogens represent the most energetic metalloids. Their atoms have seven electrons in their outer orbit. They react with hydrogen and metals as univalent negative ions. The ease with which electron attachment occurs decreases with increasing atomic weight, and along with this, the energy of halogens in relation to hydrogen and metals and the strength of these compounds also decrease. Compounds of halogens with hydrogen are gaseous and have acidic properties in aqueous solution. When interacting with metalloids, halogens form positive ions, losing their outer electrons partially or completely. With an increasing atomic weight, the ability of halogens to form a positive ion, and consequently their energy in relation to oxygen and metalloids, increases. Halogen oxides have an acidic character. Regarding the application of halogens, chlorine is widely used for bleaching, disinfection, and as a suffocating gas; some of its compounds have medical significance. Bromine and iodine compounds are used in medicine and photography.