Fluorine

=**__Flourine__**= Fluorine is an element with the atomic number of 9 and is represented as "F" on the periodic table. At standard temperature and pressure Fluorine is a yellow gas that can be found in the Earth's crust and is the 13th most abundant element. Due to it's high re-activity it's often found as fluoride. It was first used in 1530 in smelting because it lowered the melting point of metals. It was also used in Urainium enrichment in the Manhattan Project in 1886. Organic Fluorine have high chemical and thermal stability and repel water. The most commonly used is Freon in refrigeration.


 * Atomic Number:** 9
 * Atomic Weight:** 18.9984032
 * Melting Point:** 53.53 K (-219.62°C or -363.32°F)
 * Boiling Point:** 85.03 K (-188.12°C or -306.62°F)
 * Density:** 0.001696 grams per cubic centimeter
 * Phase at Room Temperature:** Gas
 * Element Classification:** Non-metal
 * Period Number:** 2
 * Group Number:** 17
 * Group Name:** Halogen

Fluorine is added to city water supplies in the form of fluoride in the proportion of about one part per million to help prevent __tooth decay__. Sodium fluoride (NaF), stannous(II) fluoride (SnF2) and sodium monofluorophosphate (Na2PO3F) are all fluorine compounds added to toothpaste, also to help prevent tooth decay. Hydrofluoric acid (HF) is used to etch glass, including most of the glass used in light bulbs. Uranium hexafluoride (UF6) is used to separate isotopes of uranium. Crystals of calcium fluoride (CaF2), also known as fluorite and fluorspar, are used to make lenses to focus infrared light. Fluorine joins with carbon to form a class of compounds known as fluorocarbons. Some of these compounds, such as dichlorodifluoromethane (CF2Cl2), were widely used in __air conditioning__ and refrigeration systems and in aerosol spray cans, but have been phased out due to the damage they were causing to the earth's ozone layer. Source: []
 * Uses:**
 * fluorine and its compounds are used in producing isotopically fractionated uranium (from UF6)
 * commercial fluorochemicals, including many well known high-temperature plastics
 * hydrofluoric acid is extensively used for etching the glass of __light bulbs__, etc.
 * fluorochloro hydrocarbons are used extensively in air conditioning and refrigeration
 * in small amounts, fluorides in water sources prevent tooth decay. A constituent of toothpaste for the same reason. Soluble fluoride in drinking water (2 ppm) may cause mottled enamel in teeth of children acquiring permanent teeth.





Fluorine is added to city water supplies in the proportion of about one part per million to help prevent tooth decay. Sodium fluoride (NaF), stannous(II) fluoride (SnF 2 ) and sodium monofluorophosphate (Na 2 PO 3 F) are all fluorine compounds added to toothpaste, also to help prevent tooth decay. Hydrofluoric acid (HF) is used to etch glass, including most of the glass used in light bulbs. Uranium hexafluoride (UF 6 ) is used to separate [|isotopes] of [|uranium]. Crystals of calcium fluoride (CaF 2 ), also known as fluorite and fluorspar, are used to make lenses to focus infrared light. Fluorine joins with [|carbon] to form a class of compounds known as fluorocarbons. Some of these compounds, such as dichlorodifluoromethane (CF 2 Cl 2 ), were widely used in air conditioning and refrigeration systems and in aerosol spray cans, but have been phased out due to the damage they were causing to the earth's ozone layer.

A fluorine atom has nine protons and nine electrons, arranged in electronic configuration [He]2s22p5, one fewer than neon. Fluorine's outer electrons are relatively separate from each other, and thus they do not shield each other from the nucleus. Therefore, they experience a relatively high effective nuclear charge. Because of this, fluorine is reluctant to ionize and has an attraction for one more electron to achieve the extremely stable neon-like arrangement. Fluorine's first ionization energy (energy required to remove an electron to form F+) is 1,681 kilojoules per mole, which is higher than for any other element except neon and helium. The second and third ionization energies of fluorine are 3,374 and 6,147 kilojoules per mole, respectively. Fluorine's electron affinity (energy released by adding an electron to form F–) is 328 kilojoules per mole, which is higher than that of any other element except chlorine. Fluorine has a relatively small covalent radius, about 60 picometers, which is more than neon and less than oxygen.
 * Electronic Structure:**