An Overview about the Chemical Element Sulfur

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Symbol: S

Atomic Number: 16

Atomic Mass: 32.066 amu (atomic mass units)

Melting Point: 115.21 C (388.36 K, 239.38 F)

Boiling Point: 444.6 C (717.75 K, 832.28 F)

Number of Protons: 16

Number of Electrons: 16

Number of Neutrons: 16

Classification: Non Metal

Group Name: Chalcogen

Crystal Structure: Orthorhombic

Density @ 293 K: 2.07 grams per cubic centimeter

Color: yellow

Sulfur has been known since ancient times. In Sanskrit it is called "sulvere" and the Latin word for it is "sulphurium". In the United Kingdom the spelling sulphur is still commonly used reflecting its Latin roots. The International Union for Pure and Applied Chemistry's approved spelling is sulfur. In about 1777 Antoine Lavoisier proved to the scientific community that sulfur was an element.

Sulfur is a brittle, odorless non-metal. It does not dissolve in water but can be dissolved in carbon disulphide. There are three allotropes or crystal forms of sulfur: orthorhombic, monoclinic and amorphous. The orthorhombic form is the most stable allotrope. Monoclinic sulfur exists at temperatures between 96 C and 119 C. When cooled monoclinic sulfur reverts back to the orthorhombic form. Amorphous sulfur is soft and elastic. It is formed when molten sulfur is cooled rapidly. The amorphous sulfur allotrope will revert back to the orthorhombic crystal structure over time.

The element can be found around volcanic vents and hot springs. It is also found in many minerals such as galena, gypsum, pyrite, sphalerite, cinnabar and barite. Sulfur can be found in meteorites and the colors seen on Jupiter's moon Io are due to some forms of sulfur.

There are four naturally occurring stable isotopes of sulphur. In order of abundance these isotopes are sulfur-32 (95.02%), sulfur-34 (4.21%), sulfur-33 (0.75%) and sulfur-35 (0.02%). Unstable isotopes with mass numbers in the range of 26 to 49 are known.

Sulfur is a biologically essential element. It is found in the amino acids methionine and cysteine. Bonds between sulfur contain amino acids known as disulfide bridges play an important part in determining a protein's tertiary structure and hence its function. Sulfur compounds are also found in fats, body fluids and some skeletal minerals.

Some bacteria use hydrogen sulfide (H2S) as an energy source. Around volcanic vents known as "black smokers" found in the oceanic depths whole communities of animal life have evolved around these bacteria. Sea creatures which have an unusual sulphur compound within them are the sea squirts (ascidians) which have sulfuric acid as part of their digestive juices.

Humans can metabolize very small amounts of hydrogen sulfide but it is lethal in any larger quantity. It kills very quickly by inhibiting respiration. Hydrogen sulfide is actually more deadly than cyanide. As hydrogen sulfide smells like rotten eggs one would expect people to notice the gas and leave the area before poisoning can occur. Unfortunately it deadens the sense of smell quite quickly so leaving its victims unaware of its presence.

Sulfur dioxide (SO2) is a found in atmospheric air pollution. The gas will dissolve in water to form the weak acid, sulfurous acid (H2SO3), which is a major factor in acid rain.

Most of the world's production of sulfur is from deposits found underground which are frequently associated with salt deposits. Such salt domes are found along the Gulf Coast of the USA. About a quarter of the worlds supply comes as a by product from the petroleum industry and metal extraction from minerals which also contain sulfur.

The main use for sulfur is the production of sulfuric acid (H2SO4) Sulfuric acid is used in many industries such as the production of fertilizers and lead-acid batteries. The annual production of sulfuric acid is 40 million tons.

There are some other uses for sulfur

* Sulfur is also used in the vulcanization process of natural rubbers.

* It has a long and continuing history of use as an insecticide. It was used as such by the ancient Greeks. Homer, the poet who wrote "The Iliad" and "The Odyssey" wrote of "pest-averting sulphur".

* Sulfur is used to make gun powder.

* Sulfur is also a dyeing agent.

* Sulfur dioxide is used as a disinfectant and a bleaching agent. It can also be used as a refrigerant.

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