Element Fluorine, F, Halogene

To the group of halogen elements there must also be added the element fluorine, which differs in its properties more widely from the other three than these from one another. It exhibits, however, still fewer relationships with the rest of the elements, and is, therefore, most suitably classed along with the halogens.

Fluorine has the combining weight 19, which is smaller than that of the other halogens. The relation which is found here, that the element with the smallest combining weight shows less similarity to the related elements than the elements of higher combining weight to one another, is repeatedly found. Reference will, therefore, be made to this again on other occasions.

Fluorine is not found free in nature any more than the other halogens. To a still higher degree than these, it has the tendency to combine with other elements. This property is so marked that until a few years ago it was quite unknown in the free state.

Compounds of fluorine are fairly widely distributed in nature. It occurs in small quantity in many rocks, and its calcium compound, fluorspar, is a very abundant mineral. The total amount of fluorine, however, in the earth's crust accessible to us is considerably less than that of chlorine.

Fluorine in the form of fluorspar also called fluorite CaF₂, was described in the end of 15^th century. Karl Wilhelm Scheele would experiment with hydrofluoric acid, easily obtained by treating calcium fluoride (fluorspar) with concentrated sulfuric acid. In 1886, elemental fluorine was isolated by Henri Moissan by electrolysis of liquid anhydrous mixture of hydrogen fluoride with small amount of potassium fluoride.

In Russian and some other languages fluorine is called "phthoros". This name, derived from Greek φθορος (disrupting, wrecking, decay), was proposed by Andre Ampere in 1810. The English fluorine comes from Latin fluere, meaning "to flow", and the name which reflects the early use of fluorite CaF₂ as a flux, to lessen the temperature of ore melting and to increase its fluidity.

The fluorine chemistry had been developed since 1930-s, especially during the World War 2 and after it in connection with growing demands of nuclear industry and rocket technology.

The average crustal abundance (clarke) of fluorine is 6.25x10^-2 mass %. In acid igneous rocks (granites) it reaches 8x10^-2 %, in basic igneous rocks (example basalt) it equals 3.7x10^-2 %, and in ultrabasic - 1x10^-2 %. Fluorite is abundant in volcanic rocks and thermal waters. The most important compounds are fluorite, cryolite and topaz. In total 86 fluorine-containing minerals are known. Fluorine compounds are also found in apatites, phosphorites etc. At the same time fluorite is very important biogenic element. The main sources which provide biosphere with fluorine are volcano eruptions.

Average content of fluorine in soil is 0.02%.

Each litre of sea water contains 0.3 mg of fluorine, and 20 times of that amount is found in oyster shells. Millions of tons of fluorides are found in coral reefs. Crustal abundance of fluorite is in average 200 times of those in living organisms.

Fluorine is a permanent trace constituent of living organisms. Significant quantities of it may be found as inorganic compounds in bones and, especially, in teeth. Sea creatures' bones are enriched with fluorine. Drinking water is the main source of fluorine in human and animals bodies. The optimal amount in water is 1-1.5 mg/l. Lack of fluorine in human body leads to teeth decay (caries). Dental fluorosis occurs because of the excessive intake of fluorine. High concentrations of fluorine ions are dangerous because of their ability to inhibit enzymatic reactions and to bind some biologically important elements, such as phosphorus, calciumalcium, magnesium, etc., creating their imbalance in organism. Organic fluorine compounds are found only in some plants, for instance, in South African Dichapetalum cymosum. The main organic compounds are fluoroacetic acid derivatives, very toxic for other plants as well as for animals.

The exploration of biological role of fluorine is still incomplete. The importance of fluorine metabolism in creation of bone tissue and teeth is confirmed. The necessity of this element for plants is not proved.