For example, graphite can be oxidised by hot concentrated nitric acid at standard conditions to mellitic acid, C 6(CO 2H) 6, which preserves the hexagonal units of graphite while breaking up the larger structure. Graphite is much more reactive than diamond at standard conditions, despite being more thermodynamically stable, as its delocalised pi system is much more vulnerable to attack. Carbon also has the highest sublimation point of all elements. Carbon is a component element in the large majority of all chemical compounds, with about two hundred million examples having been described in the published chemical literature. It bonds readily with other small atoms, including other carbon atoms, and is capable of forming multiple stable covalent bonds with suitable multivalent atoms. The allotropes of carbon include graphite, one of the softest known substances, and diamond, the hardest naturally occurring substance. Newer work indicates that the melting point of diamond (top-right curve) does not go above about 9000 K. Theoretically predicted phase diagram of carbon, from 1989. Carbon forms a vast number of compounds, with about two hundred million having been described and indexed and yet that number is but a fraction of the number of theoretically possible compounds under standard conditions. The largest sources of inorganic carbon are limestones, dolomites and carbon dioxide, but significant quantities occur in organic deposits of coal, peat, oil, and methane clathrates. The most common oxidation state of carbon in inorganic compounds is +4, while +2 is found in carbon monoxide and transition metal carbonyl complexes. They are chemically resistant and require high temperature to react even with oxygen. All carbon allotropes are solids under normal conditions, with graphite being the most thermodynamically stable form at standard temperature and pressure. Under normal conditions, diamond, carbon nanotubes, and graphene have the highest thermal conductivities of all known materials. Graphite is a good electrical conductor while diamond has a low electrical conductivity. Graphite is soft enough to form a streak on paper (hence its name, from the Greek verb "γράφειν" which means "to write"), while diamond is the hardest naturally occurring material known. For example, graphite is opaque and black, while diamond is highly transparent. The physical properties of carbon vary widely with the allotropic form. Well-known allotropes include graphite, diamond, amorphous carbon, and fullerenes. The atoms of carbon can bond together in diverse ways, resulting in various allotropes of carbon. It is the second most abundant element in the human body by mass (about 18.5%) after oxygen.
Carbon's abundance, its unique diversity of organic compounds, and its unusual ability to form polymers at the temperatures commonly encountered on Earth, enables this element to serve as a common element of all known life. Ĭarbon is the 15th most abundant element in the Earth's crust, and the fourth most abundant element in the universe by mass after hydrogen, helium, and oxygen. Carbon is one of the few elements known since antiquity. Three isotopes occur naturally, 12C and 13C being stable, while 14C is a radionuclide, decaying with a half-life of about 5,730 years.
Carbon makes up about 0.025 percent of Earth's crust. It belongs to group 14 of the periodic table. It is nonmetallic and tetravalent-its atom making four electrons available to form covalent chemical bonds. −4, −3, −2, −1, 0, +1, +2, +3, +4 (a mildly acidic oxide)Ĭarbon (from Latin carbo 'coal') is a chemical element with the symbol C and atomic number 6.
0 kommentar(er)
