# Structural Biochemistry/Inorganic Chemistry/Nonmetals/Halogens
## Halogens

The Halogens are:
* Fluorine (F)
* Chlorine (Cl)
* Bromine (Br)
* Iodine (I)
* Astatine (At)
The halogens are a part of the 17th group of the periodic table of the elements. The halogens have varying physical properties; at room temperature fluorine and chlorine are gasses, bromine is a liquid, and iodine is a solid. On the other hand, they are very similar in their chemical properties. Any of the halogens will react with any of the alkali metals in a 1:1 ratio to form an alkali halide. Examples of some of these salt compounds are NaCl, LiF, and RbI.
Reactivity:
Halogens are extremely electronegative which means that they are highly reactive since they are only one electron away from filling their outer most electron shell. The halogen fluorine is one of the most reactive elements and has to be handled with care. The storing of fluorine is very difficult because it could react with glass if it has any water in it so it is usually stored in a container lined with a fluoride compounds. Chlorine and Bromine can be used as a sterilizer by their high reactivity. Iodine could also be used as sterilization for the skin.
Besides, halogens mean "salt formers" and the compounds that contain halogens are also called "salts." All of the halogens have seven electrons in their outer shells, which give them an oxidation number of -1. Also, at room temperature, the halogens exist in all three states: liquid, solid, and gas. The gas state include fluorine and chlorine, liquid state include bromine, and the solid state include iodine and astatine.

## Fluorine

Fluorine's atomic number is 9. It can make a single bond with itself. It's characteristics are a poisonous yellow brown gas that is very reactive. At room temperature Fluoride in the gas phase.
Fluoride is the reduced form of fluorine and consumption of this ion can have toxic affects on the human body. Despite its toxicity, fluoride can be found in many everyday products including, toothpaste, vitamin supplements, baby formulas, and even public water. Many dental products contain fluoride in order to prevent tooth decay, but an over consumption can be fatal. Effects include birth defects, osteoarthritis, bone and uterine cancer, and skeletal fluorsis. Fluoride poisoning can be tested in medical laboratories by measuring the amounts of potassium and calcium in blood samples. Too little calcium and too much potassium may be signs that a person has been exposed to too much fluoride.

## Applications of Fluorine

There are tons of compounds that involve the element fluorine and many of those compounds are useful for research. One such example is cryolite. Cryolite is a sodium-aluminium-fluoride compound that is used in the Hall-Heroult Process, where one takes cryolite and combine it with molten alumina followed by electrolysation. This leads to a collection of aluminum metal at the cathode of the electrophersis. This is an industrial method to produce pure aluminum by using a fluoride precursor. Another important daily use of a fluorine compound is sodium fluoride. This compound serves two purposes in the sense that it is present in the enamel of the tooth in the form of fluoroapatite. By fluorinating the water, people who use the water would have the benefits of fluorine, providing extra strength to the teeth. The other major use is the active ingredient in toothpaste. In toothpaste, the sodium fluoride acts as an active ingredient to dissociate water. This dissociation causes the separation of the fluorine atom enabling it to be absorbed into the bone of your teeth, enhancing the strength. more complex compounds containing fluorine which are used both in the industrial setting and in household environments include polytetrafluoroethylene, most commonly known as Teflon. In addition many refrigerants use fluorine, as well as in fire extinguishing reagent and propellant in aerosol sprays.

## Chlorine

Chlorine's atomic number is 17. It is abundant in nature since it is part of common salts, such as sodium chloride (NaCl). In its elemental form it can be seen as a pale green gas. Chlorine is also in the gas phase at room temperature.
In biological systems, chlorine accounts for about 0.15% of the human body weight. Chlorine is primarily used in the production of hydrochloric acid which is secreted from the parietal cells in the stomach and is used in maintaining the acidic environment for pepsin. It plays a vital role in maintaining the proper acid-base balance of body fluids. It is absorbed in the intestine and secreted through urine, sweat, vomit and diarrhea.
A deficiency in chlorine can lead to a condition called metabolic alkalosis where the pH of the blood is higher than normal. Symptoms include: decrease in ventilation, acidic urine, and excessive excretion of potassium.
Atomic chlorine can also be linked to the depletion of ozone. Chlorofluorocarbons (CFCs), which are originally used in refrigerators and air conditioners, escape and rise into the stratosphere are then decomposed by UV light from the sun to form atomic Cl. The newly formed atomic chloride is then able to react with ozone (O$_3$), thus depleting the ozone concentration in the stratosphere and forming oxygen gas (O$_2$).

## Bromine

Bromine's atomic number is 35. At room temperature it is a reddish-brown liquid. The vapors from bromine are corrosive and toxic. Bromine is the only halogen that is liquid at room temperature. It has a similarly colored vapor with an offensive and suffocating odor. It is the only nonmetallic element that is liquid under ordinary conditions, it evaporates easily at standard temperature and pressures in a red vapor that has a strong disagreeable odor resembling that of chlorine. Bromine is less active chemically than chlorine and fluorine but is more active than iodine; its compounds are similar to those of the other halogens. Bromine is soluble in organic solvents and in water.
Read more: http://www.lenntech.com/periodic/elements/br.htm#ixzz2Aem37Fo2

## Iodine

Iodine's atomic number is 53. At room temperature it is a dark purple-grey solid and is the heaviest element in a living organism.
Iodine is an essential mineral for the body. It is heavily used in the thyroid gland, but also can be found in breast tissue, salivary gland, and adrenal gland. Without iodine, thyroid hormones cannot be produce and this can lead to a condition called hypothyroidism. Without treatment, the thyroid gland will swell and produce a visible goiter. Children with hypothyroidism may develop mental retardation. In women, hypothyroidism can lead to infertility, miscarriages, breast, and ovarian cancer. Thyroid problems have been common issue for many years particularly in middle aged women. Correlated studies have shown that iodine levels in the general population have been significantly decreased in recent years. Most salt has iodine and with current health problems, many people have been consuming less salt, and therefore in-taking less iodine.

## Applications of Iodine

Due to its lower oxidizing power compared to fluorine and chlorine, there not as much applications of this halogen as compared to the ones mentioned above, as most of the applications of halogens are derived from their oxidizing power. Nonetheless, iodine has its applications in the medical field. The solution of iodine and potassium iodine forms the solution better known as "Lugol"s iodine, which is present in emergency safety kits for the purpose of disinfecting wounds and disinfecting water by killing bacteria that may be present. The other use of iodine in the medical field is te generation of certain thyroid hormones from iodine derivatives. Thyroid hormones such as thyroxine and triiodothronine are dependent on a source of a small amount of iodine. a deficiency of iodine would usually involve in the development in "goitre" or a swelling in the thyroid gland and the laryx. In order to prevent such a swelling, it is recommended to consume more seafood seeing as how the ocean water naturally contains more iodine, the sea life would contain more percent iodine if consumed and absorbed in the body.

## Astatine

Astatine's atomic number is 85. This element is radio active and was only discovered because radioactivity in nature. Is is also the heaviest halogen but only small amounts are found at a time because it has a short half life. It is just presumed to be a black solid. At room temperature Astatine exists as a solid. An image of Astatine can be found here :Astatine
Hydrogen halides
Hydrogen halides are HF, HCL, HBr, HI, and HAt which are very strong acids because the can dissociate completely into ions.

## References

http://www.globalhealingcenter.com/natural-health/how-safe-is-fluoride/ http://www.springboard4health.com/notebook/min_chloride.html
Bradley, Rachelle. "IODINE DEFICIENCY AND YOUR HEALTH: Hypothyroidism, Thyroid Disease and Fibrocystic Breast Disease." Heartland Naturopathic Clinic. n. page. Web. 30 Nov. 2011. <http://www.heartlandnaturopathic.com/Iodine.htm>
Oxtoby, David. (2008). Principles of Modern Chemistry, 6th Ed., ISBN0-534-49366-1.
"Production and use of Chlorofluorocarbons". CIESIN Thematic Guides. http://www.ciesin.org/TG/OZ/prodcfcs.html