Introduction: Fluorine has the differentiation of being the most reactive of all the elements. with the highest electronegativity value on the periodic tabular array. Because of this. it proved highly hard to insulate. Davy foremost identified it as an component. but was poisoned while seeking unsuccessfully to break up H fluoride. Two other chemists were besides subsequently poisoned in similar efforts. and one of them died as a consequence. Gallic chemist Edmond Fremy ( 1814-1894 ) really about succeeded in insulating F. and though he failed to make so. he inspired his pupil Henri Moissan ( 1852-1907 ) to go on the undertaking.
One of the jobs involved in insulating this extremely reactive component was the fact that it tends to “attack” any container in which it is placed: most metals. for case. will split into fires in the presence of F. Like the others before him. Moissan set about to insulate F from H fluoride by agencies of electrolysis—the usage of an electric current to do a chemical reaction—but in making so. he used a platinum-iridium metal that resisted onslaughts by F. In 1906. he received the Nobel Prize for his work. and his technique is still used today in modified signifier.
Properties And Uses Of Fluorine: A picket green gas of low denseness. F can unite with all elements except some of the baronial gases. Even H2O will fire in the presence of this extremely reactive substance. Fluorine is besides extremely toxic. and can do terrible Burnss on contact. yet it besides exists in harmless compounds. chiefly in the mineral known as fluorite. or calcium fluoride. The latter gives off a fluorescent visible radiation ( fluorescence is the term for a type of light non accompanied by heat ) . and F was named for the mineral that is one of its chief “hosts” .
Get downing in the 1600s. hydrofluoric acid was used for etching glass. and is still used for that intent today in the industry of merchandises such as light bulbs. The oil industry uses it as a catalyst—a substance that speeds along a chemical reaction—to increase the octane figure in gasolene. Fluorine is besides used in a polymer normally known as Teflon. which provides a non-stick surface for frying pans and other cooking-related merchandises. Just as Cl proverb service in World War I. F was enlisted in World War II to make a arm far more terrific than toxicant gas: the atomic bomb.
Scientists working on the Manhattan Project. the United States’ attempt to develop the bombs dropped on Japan in 1945. needful big measures of the uranium-235 isotope. This they obtained in big portion by diffusion of the compound uranium hexafluoride. which consists of molecules incorporating one U atom and six fluorine anions. Fluoridation Of Water: Long before World War II. wellness functionaries in the United States noticed that communities holding high concentration of fluoride in their imbibing H2O tended to endure a much lower incidence of tooth decay.
In some countries the concentration of fluoride in the H2O supply was high plenty that it stained people’s dentitions ; still. at the bend of the century—an epoch when dental hygiene as we know it today was still in its infancy—the bar of tooth decay was an attractive chance. Possibly. functionaries surmised. it would be possible to present smaller concentrations of fluoride into community imbibing H2O. with a ensuing betterment in overall dental wellness.
After World War II. a figure of municipalities around the United States ndertook the fluoridization of their H2O supplies. utilizing concentrations every bit low as 1 ppm. Within a few old ages. fluoridization became a heatedly debated subject. with advocates indicating to the possible wellness benefits and oppositions reasoning from the point of view of issues non straight involved in scientific discipline. It was an invasion of personal autonomy. they said. for authoritiess to coerce citizens to imbibe H2O which had been supplemented with a foreign substance. During the 1950s. in fact. fluoridization became associated in some circles with Communism—just another manifestation of a authorities seeking to command its citizens.
In ulterior old ages. ironically. antifluoridation attempts became associated with groups on the political left instead than the right. By so. the statement no longer revolved around the issue of authorities power ; alternatively the concern was for the wellness hazards involved in presenting a substance lethal in big doses. Fluoride had meanwhile gained application in toothpastes. Colgate took the lead. presenting “stannous fluoride” in 1955.
Three old ages subsequently. the company launched a memorable advertisement run with commercials in which a small miss showed her female parent a “report card” from the tooth doctor and announced “Look. Ma! No pits! ” Within a few old ages. virtually all trade names of toothpaste used fluoride ; nevertheless. the usage of fluoride in imbibing H2O remained controversial. Equally late as 1993. in fact. the issue of fluoridization remained het plenty to engender a survey by the U. S. National Research Council. The council found some betterment in dental wellness. but non every bit big as had been claimed by early advocates of fluoridization. Furthermore. this betterment could be explained by mention to a figure of other factors. including fluoride in toothpastes and a by and large heightened consciousness of dental wellness among the U. S. public.
Chlorofluorocarbons: Another controversial application of F is its usage. along with Cl and C. in CFCs. As celebrated above. Chlorofluorocarbons have been used in refrigerants and propellents ; another application is as a blowing agent for polyurethane froth. This continued for several decennaries. but in the 1980s. conservationists became concerned over depletion of the ozone bed high in Earth’s atmosphere. Unlike ordinary O ( O 2 ) . ozone or O 3 is capable of absorbing ultraviolet radiation from the Sun. which would otherwise be harmful to human life.
It is believed that Chlorofluorocarbons catalyze the transition of ozone to O. and that this may explicate the “ozone hole. ” which is peculiarly noticeable over the Antarctic in September and October. As a consequence. a figure of states signed an understanding in 1996 to extinguish the industry of halocarbons. or substances incorporating halogens and C. Manufacturers in states that signed this understanding. known as the Montreal Protocol. have developed CFC replacements. most notably HCFCs ( HCFCs ) . CFC-like compounds besides incorporating H atoms.
The ozone-layer inquiry is far from settled. nevertheless. Critics argue that in fact the depletion of the ozone bed over Antarctica is a natural happening. which may explicate why it merely occurs at certain times of twelvemonth. This may besides explicate why it happens chiefly in Antarctica. far from any topographic point where worlds have been utilizing CFCs. ( Ozone depletion is far less important in the Arctic. which is much closer to the population centres of the industrialised world. ) In any instance. natural beginnings. such as vent eruptions. go on to add halogen compounds to the ambiance.
Introduction: Chlorine is a extremely toxicant gas. greenish-yellow in colour. with a crisp odor that induces choking in worlds. Yet. it can unite with other elements to organize compounds safe for human ingestion. Most noteworthy among these compounds is salt. which has been used as a nutrient preservative since at least 3000 B. C. Salt. of class. occurs in nature. By contrast. the first Cl compound made by worlds was likely hydrochloric acid. created by fade outing H chloride gas in H2O.
The first scientist to work with hydrochloric acid was Iranian doctor and alchemist Rhazes ( ar-Razi ; c. 64-c. 935 ) . one of the most outstanding scientific heads of the mediaeval period. Alchemists. who in some ways were the precursors of true chemists. believed that base metals such as Fe could be turned into gold. Of class this is non possible. but alchemists in about 1200 did at least win in fade outing gold utilizing a mixture of hydrochloric and azotic acids known as aqua regia. The first modern scientist to work with Cl was Swedish chemist Carl W. Scheele ( 1742-1786 ) . who besides discovered a figure of other elements and compounds. including Ba. manganese. O. ammonium hydroxide. and glycerol.
However. Scheele. who isolated it in 1774. idea that Cl was a compound ; merely in 1811 did English chemist Sir Humphry Davy ( 1778-1829 ) place it as an component. Another chemist had suggested the name “halogen” for the alleged compound. but Davy suggested that it be called chlorine alternatively. after the Grecian word chloros. which indicates a sickly xanthous colour. Uses Of Chlorine: The dangers involved with Cl have made it an effectual substance to utilize against discolorations. workss. animals—and even human existences.
Chlorine gas is extremely annoying to the mucose membranes of the olfactory organ. oral cavity. and lungs. and it can be detected in air at a concentration of merely 3 parts per million ( ppm ) . The concentrations of Cl used against military personnels on both sides in World War I ( get downing in 1915 ) was. of class. much higher. Thankss to the usage of Cl gas and other antipersonnel agents. one of the most scarey images to emerge from that struggle was of soldiers yielding to toxicant gas. Yet merely as it is harmful to worlds. Cl can be harmful to microbes. therefore continuing human life.
Equally early as 1801. it had been used in solutions as a germicide ; in 1831. its usage in infirmaries made it effectual as a arm against a cholera epidemic that swept across Europe. Another well-known usage of Cl is as a bleaching agent. Until 1785. when Cl was foremost put to utilize as a bleach. the lone manner to acquire discolorations and unwanted colourss out of fabrics or paper was to expose them to sunlight. non ever an effectual method.
By contrast. Cl. still used as a bleach today. can be extremely effective—a good ground non to utilize regular antique bleach on anything other than white vesture. Since the 1980s. shapers of bleaches have developed all-color versions to lighten up and take out discolorations from vesture of other colors. ) Calcium hydrocholoride ( CaOCl ) . both a bleaching pulverization and a germicide used in swimming pools. combines both the germicide and decoloring belongingss of Cl. This and the others discussed here are merely some of many. many compounds formed with the extremely reactive component Cl. Particularly notable—and controversial—are compounds affecting Cl and C. Chlorine And Organic Compounds:
Chlorine bonds good with organic substances. or those incorporating C. In a figure of cases. Cl becomes portion of an organic polymer such as PVC ( polyvinyl chloride ) . used for doing man-made pipe. Chlorine polymers are besides applied in doing man-made gum elastic. or neoprene. Due to its opposition to heat. oxidization. and oils. neoprene is used in a figure of car parts. The bonding of Cl with substances incorporating C has become progressively controversial because of concerns over wellness and the environment. and in some instances chlorine-carbon compounds have been outlawed.
Such was the destiny of DDT. a pesticide soluble in fats and oils instead than in H2O. When it was discovered that DDT was carcinogenic. or cancer-causing. in worlds and animate beings. its usage in the United States was outlawed. Other. less well-known. chlorine-related insect powders have similarly been banned due to their possible for injury to human life and the environment. Among these are chlorine-containing stuffs one time used for dry cleansing. Besides noteworthy is the function of Cl in CFCs ( CFCs ) . which have been used in refrigerants such as Freon. and in propellents for aerosol sprays. Chlorofluorocarbons tend to vaporize easy. and concerns over their consequence on Earth’s atmosphere have led to the phasing out of their usage.
Introduction: Bromine is a fetid red-brown liquid whose name is derived from a Grecian word significance “stink. ” With a boiling point much lower than that of water—137. 84°F ( 58. 8°C ) —it readily transforms into a gas. Like other halogens. its bluess are extremely annoying to the eyes and pharynx. It is found chiefly in sedimentations of seawater. a solution of salt and H2O. Among the most important seawater sedimentations are in Israel’s Dead Sea. every bit good as in Arkansas and Michigan.
Recognition for the isolation of Br is normally given to Gallic chemist Antoine-Jerome Balard ( 1802-1876 ) . though in fact German chemist Carl Lowig ( 1803-1890 ) really isolated it foremost. in 1825. However. Balard. who published his consequences a twelvemonth subsequently. provided a much more elaborate account of bromine’s belongingss. The first usage of Br really predated both work forces by several millenaries. To do their celebrated violet dyes. the Phoenicians used murex molluscs. which contained Br. ( Like the names of the halogens. the word “Phoenicians” is derived from Greek—in this instance. a word significance “red” or “purple. ” which referred to their dyes.
Today Br is besides used in dyes. and other modern utilizations include applications in pesticides. germicides. medical specialties. and flame retardents. At one clip. a compound incorporating Br was widely used by the crude oil industry as an additive for gasolene incorporating lead. Ethylene dibromide reacts with the lead released by gasolene to organize lead bromide ( PbBr 2 ) . referred to as a “scavenger. ” because it tends to clean the emanations of lead-containing gasolene. However. leaded gasolene was phased out during the late seventiess and early 1980s ; as a consequence. demand for ethylene dibromide dropped well. Halogen Lamps:
The name “halogen” is likely familiar to most people because of the term “halogen lamp. ” Used for car headlamps. limelights. and flood lamps. the halogen lamp is much more effectual than ordinary incandescent visible radiation. Incandescent “heat-producing” visible radiation was first developed in the 1870s and improved during the early portion of the 20th century with the replacing of C by wolfram as the chief stuff in the fibril. the country that is heated. Tungsten proved much more lasting than C when heated. but it has a figure of jobs when combined with the gases in an incandescent bulb.
As the light bulb continues to fire for a period of clip. the tungsten fibril begins to thin and will finally interrupt. At the same clip. tungsten begins to roll up on the surface of the bulb. diping its visible radiation. However. by adding Br and other halogens to the bulb’s gas filling—thus doing a halogen lamp—these jobs are alleviated. As tungsten evaporates from the fibril. it combines with the halogen to organize a gaseous compound that circulates within the bulb. Alternatively of lodging on the surface of the bulb. the compound remains a gas until it comes into contact with the fibril and interrupt down.
It is so redeposited on the fibril. and the halogen gas is free to unite with freshly evaporated wolfram. Though a halogen bulb does finally interrupt down. it lasts much longer than an ordinary incandescent bulb and Burnss with a much brighter visible radiation. Besides. because of the reduced wolfram sedimentations on the surface. it does non get down to dip as it nears the terminal of its life.
Introduction: First isolated in 1811 from ashes of seaweed. I has a name derived from the Grecian word intending “violet-colored”—a mention to the fact it forms dark violet crystals. During the 1800s. I was obtained commercially from mines in Chile. but during the 20th century Wellss of seawater in Japan. Oklahoma. and Michigan have proven a better beginning. Uses And Applications: Among the best-known belongingss of I is its importance in the human diet. The thyroid secretory organ produces a growth-regulating endocrine that contains I. and deficiency of I can do a goitre. a swelling around the cervix. Table salt does non of course contain I ; nevertheless. Na chloride sold in shops normally contains about 0. 01 % Na iodide. added by the maker.
Iodine was one time used in the development of picture taking: During the early yearss of photographic engineering. the daguerreotype procedure used Ag home bases sensitized with iodine bluess. Iodine compounds are used today in chemical analysis and in synthesis of organic compounds.
Introduction: Merely as F has the differentiation of being the most reactive. At is the rarest of all the elements. Long after its being was predicted. chemists still had no fortune happening it in nature. and it was merely created in 1940 by pelting Bi with alpha atoms ( positively charged He karyon ) .
The freshly isolated component was given a Grecian name intending “unstable. ” Indeed. none of astatine’s 20 known isotopes is stable. and the longest-lived has a half life of merely 8. 3 hours. This has merely added to the troubles involved in larning about this unusual component. and therefore it is hard to state what applications. if any. At may hold. The most promising country involves the usage of At to handle a status known as thyrotoxicosis. related to an excessively active thyroid secretory organ.