Hence the heavier halogens also form compounds in positive oxidation states (+1, +3, +5, and +7), derived by the formal loss of ns and np electrons.įluorine is the most reactive element in the periodic table, forming compounds with every other element except helium, neon, and argon. The halogens all have relatively high ionization energies, but the energy required to remove electrons decreases substantially as we go down the column. Notice, however, that all the halogens except astatine have electronegativities greater than 2.5, making their chemistry exclusively that of nonmetals. †The values cited are for the six-coordinate anion (X −).īecause it is the most electronegative element in the periodic table, fluorine forms compounds in only the −1 oxidation state. *The configuration shown does not include filled d and f subshells. Standard reduction potential ( E°, V) (X 2 → X − in basic solution) Table 22.6 Selected Properties of the Group 17 Elements Property
Fluorine is also found in teeth as fluoroapatite, which is formed by reacting hydroxyapatite in tooth enamel with fluoride ions in toothpastes, rinses, and drinking water. Large amounts of fluorine are now consumed in the production of cryolite (Na 3AlF 6), a key intermediate in the production of aluminum metal.
For this achievement, among others, Moissan narrowly defeated Mendeleev for the Nobel Prize in Chemistry in 1906. After being poisoned three times while trying to isolate the element, the French chemist Henri Moissan succeeded in 1886 in electrolyzing a sample of KF in anhydrous HF to produce a pale green gas ( Figure 22.14 "Isolation of Elemental Fluorine"). Elemental fluorine proved to be very difficult to isolate, however, because both HF and F 2 are extraordinarily reactive and toxic. The solution was later recognized to contain the acid of a new element, which was named fluorine in 1812. In 1670, a German glass cutter discovered that heating fluorspar with strong acid produced a solution that could etch glass. The mineral fluorspar (now called fluorite ) had been used since the 16th century as a “flux,” a low-melting-point substance that could dissolve other minerals and ores. He soon realized, however, that he had discovered a new element, which he named bromine from the Greek bromos, meaning “stench.” Currently, organic chlorine compounds, such as PVC (polyvinylchloride), consume about 70% of the Cl 2 produced annually organobromine compounds are used in much smaller quantities, primarily as fire retardants.īecause of the unique properties of its compounds, fluorine was believed to exist long before it was actually isolated.
Because many of its properties were intermediate between those of chlorine and iodine, Balard initially thought he had isolated a compound of the two (perhaps ICl). A deep purple vapor was released, which had a biting aroma similar to that of Scheele’s “compound.” The purple substance was identified as a new element, named iodine from the Greek iodes, meaning “violet.” Bromine was discovered soon after by a young French chemist, Antoine Jérôme Balard, who isolated a deep red liquid with a strong chlorine-like odor from brine from the salt marshes near Montpellier in southern France. That same year, a French industrial chemist, Bernard Courtois, accidentally added too much sulfuric acid to the residue obtained from burned seaweed. In 1811, Scheele’s “compound” was identified as a new element, named from the Greek chloros, meaning “yellowish green” (the same stem as in chlorophyll, the green pigment in plants). Scheele was convinced, however, that the pale green gas he collected over water was a compound of oxygen and hydrochloric acid. In 1774, Carl Wilhelm Scheele (the codiscoverer of oxygen) produced chlorine by reacting hydrochloric acid with manganese dioxide.
GROUP 7 REACTIVITY TREND FREE
Because the halogens are highly reactive, none is found in nature as the free element.Ĭhlorine was the first halogen to be obtained in pure form.
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