Carbon is a chemical element with the symbol C and the atomic number 6. It has been known since ancient times. Graphite was named in 1594 by D.L.G. Harsten and A.G. Werner. Carbon was named by A.L. Lavoisier in 1789. It is a member of the non-metallic tetravalent (having 4 valence electrons) Group 14 in the periodic table which also includes silicon, germanium, tin, lead and flervium. Nine different structural forms of carbon have been identified including diamond, graphite, Lonsdaleite, Buckminsterfullerene, C-70, amorphous carbon, carbon nanotubes and grapheme. The physical properties of color, transparency, thermal conductivity, electrical conductivity, hardness vary considerablely between the different allotropes.
Carbon is a very common element found throughout the universe, solar system and the natural environment on earth. It is the 4th most abundant element by weight in the universe and the 15th most abundant element in the Earth’s crust. Carbon is extracted from deposits of coal and processed for a wide variety of commercial applications. Diamonds are a hard form of carbon created by volcanic activity.
Carbon is the stuff of life. Its four valence electrons allow it to form a wide variety of molecular structures. The DNA and RNA in the nucleus of every living cell on Earth contains carbon along with oxygen, hydrogen, nitrogen and phosphorus. The proteins that make up living creatures all contain carbon, hydrogen and nitrogen. Many compounds of carbon and hydrogen are created and utilized by plants and animals.
Carbon has 16 known isotopes which range in atomic weight from 8 to 23. C-12 and C-13 are stable naturally occurring isotopes and the rest are radioisotopes. Half-lives of the radioactive isotopes of carbon vary from C-21 with a half-life of less than 30 billionths of a second to C-14 with a half-life of 5700 years. Carbon-14 is produced by the action of cosmic rays on the Earth’s atmosphere.
Carbon-14 was discovered Carbon-14 is absorbed by all living things. When they die, they stop absorbing C-14. Therefore, the amount of C-14 found in the remains of plants and animals can be used to date them. C-14 is one of the primary tools of archeology. Some of the limitations of C-14 dating include restriction to things that were once alive, distribution throughout the sample, changes in the atmosphere that affect C-14 generation and inability to date objects older than 60,000 years which excludes the vast majority of fossils.
Carbon-11 has a half-life of about 20 minutes and it decays by positron emission to Boron-11. It is produced by proton bombardment of Nitrogen-14. C-11 accumulates preferentially in tumors. Tumors create many new proteins and C-11 absorption is an indicator of tumor growth. C-11 is useful for positron emission tomography for the early diagnosis of cancer, monitoring therapeutic response to cancer treatment and for the investigation of the biological action of anti-cancer drugs. Because of its short half-life, utilization of C-11 is dependent on the fast generation of C-11 and the compounds that contain it followed by rapid application.
