Carbon
Symbol: C
Atomic Number: 6
Atomic Mass: 12.0107 amu (atomic mass units)
Melting Point: 3500.0 C (3773.15 K, 6332.0 F)
Boiling Point: 4827.0 C (5100.15 K, 8720.6 F)
Number of Electrons: 6
Number of Protons: 6
Number of Neutrons: 6
Classification: Non Metal
Crystal Structure: Hexagonal
Density @ 293 K: 2.267 grams per cubic centimeter
Color: May be black but depends on allotrope
Carbon has been known from ancient times. Its name comes from the Latin “carbo” which means charcoal.
Carbon forms many different compounds. Nearly ten million carbon compounds have been recognized. The study of carbon and its compounds form a separate branch of chemistry known as organic chemistry. Life on earth is based on many of these organic compounds so without carbon we would not exist.
There are three naturally occurring allotropes of carbon: amorphous, graphite and diamond. The properties and uses of pure carbon differ for each allotrope.
Amorphous carbon is produced by the incomplete burning of carbon based compounds. It is commonly known as lamp black, black soot, gas black, channel black or carbon black. Amorphous carbon is used to make ink paint and some rubber products. The cores of dry cell batteries are made of pressed amorphous carbon.
Graphite is a soft platy form of carbon. It is one of the softest known minerals. Natural graphite exists in two crystal forms alpha and beta the physical properties of the two forms are identical. Most commercially available graphite is man made and is of the alpha form. Graphite is made from the tarry residue left after petroleum extraction from crude oil. The residue is heated in an oxygen free oven to produce graphite. This graphite is used as a lubricant and also to make the leads of pencils. Graphite made by heating soft coal in an oxygen free oven is called coke and is used in the steel refining industry.
While graphite is one of the softest mineral the third allotrope of carbon is diamond, the hardest mineral known. These two allotropes differ only in their crystal structure. Industrial grade diamonds are made from graphite by subjecting it to heat and pressure for days or weeks. Diamonds made from graphite are used to make cutting tools such as diamond tipped saws. Natural diamonds are cut or faceted to produce brilliant gem stones for use in jewelry. Quality natural diamonds are highly valued.
A fourth, man made, allotrope of carbon was synthesized in 1969. Known as white carbon this allotrope is transparent and can split a beam of light into two beams in a property known as birefringence.
There are two stable isotopes of carbon these are carbon -12 and carbon-13. There are a number of unstable isotopes of carbon with mass numbers that range from 8 to 22. One of these, carbon-14, has proved useful in dating some archaeological and paleontological finds.
Carbon-14 has a half life of 5730 years decaying by beta decay to form nitrogen-14. The amount of carbon-14 in the air remains fairly constant as new carbon-14 made in the upper atmosphere by the action of cosmic rays replaces the atoms that have decayed. While they are alive all living things take in a carbon-14 so the amount in their bodies is the same as that in the atmosphere. When they die no new carbon 14 can enter their remains so the amount of carbon -14 in formerly living thing falls at a constant rate. By measuring the amount of carbon-14 left an archaeologist can get an estimate of when death occurred. This technique can be used to date anything that has been made from formerly living material such as wood, skins, bone, cotton, wool, paper or papyrus.
Recently a new type of carbon molecule has been discovered. Buckminsterfullerenes, or buckyballs as they are commonly known consist of 60 or 70 carbon atoms. These molecules are shaped like a soccer ball and have the ability to trap other atoms in their framework. They have magnetic as well as superconductive properties. Buckyballs appear to be able to resist great pressures. Research into Buckyballs and their properties is continuing.
