Carbon (pronounced: /kɑɹbən/) is a chemical element with the symbol C and its atomic number is 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds. There are three naturally occurring isotopes, with C and C being stable, while C is radioactive, decaying with a half-life of about 5700 years. Carbon is one of the few elements known to man since antiquity. The name "carbon" comes from Latin language carbo, coal, and, in some Romance languages, the word carbon can refer both to the element and to coal. There are several allotropes of carbon of which the best known are graphite, diamond, and amorphous carbon. The physical properties of carbon vary widely with the allotropic form. For example, diamond is highly transparent, while graphite is opaque and black. Diamond is among the hardest materials known, while graphite is soft enough to form a streak on paper. Diamond has a very low electric conductivity, while graphite is a very good conductor. Also, diamond has the highest thermal conductivity of all known materials under normal conditions. All the allotropic forms are solids under normal conditions but graphite is the most thermodynamically stable. (via Wikipedia)