Carbon compounds have free electrons
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carbon (from altgerm. kolo = "Coal"), symbol C. (from lat. carbo "Charcoal", latinized carbonium) is a chemical element of the 4th main group. It occurs in nature both in pure (dignified) form and chemically bound. Due to its special electron configuration (half-filled L-shell) it has the ability to form complex molecules and has the greatest variety of chemical compounds of all chemical elements. Carbon compounds form the molecular basis of all earthly life.
Carbon is the most important element of the biosphere; after oxygen (water) it is the most abundant element by weight in living things. Geologically, however, it is not one of the most common elements.
All living things contain carbon, all living tissue is made up of (organic) carbon compounds. This applies to both plants, mushrooms and animals.
Geologically, carbon is found both in elemental form and in compounds. You can find both diamond and graphite in nature. The main locations of diamond are Africa (especially South Africa and the Congo) and Russia. Diamonds are often found in volcanic rocks such as kimberlite. Graphite is relatively rare in carbon-rich metamorphic rocks. The most important deposits are in India and China.
Most often, carbon is found in the form of inorganic carbonate rock (approx. 2.8 · 1016 t). Carbonate rocks are widespread and sometimes form mountains. A well-known example of carbonate mountains are the Dolomites in Italy. The most important carbonate minerals are calcium carbonate (modifications: limestone, chalk, marble) CaCO3, Calcium magnesium carbonate (dolomite) CaCO3 · MgCO3, Iron carbonate (iron spar) FeCO3 and zinc carbonate (zinc spar) ZnCO3.
Well-known carbon deposits are the fossil fuels coal, crude oil and natural gas. These are not pure carbon compounds, but a mixture of many different organic compounds. They were created by converting vegetable (coal) and animal (oil, natural gas) remains under high pressure. Important deposits for coal are in the USA, China and Russia. A well-known German coal deposit is located in the Ruhr area. The most important oil reserves are on the Arabian Peninsula (Iraq, Saudi Arabia). Other important oil deposits are in the Gulf of Mexico and in the North Sea.
Carbon continues to exist in the air as carbon dioxide. It makes up about 0.04% of the composition of the air. Carbon dioxide is produced when carbon-containing compounds are burned. There is also CO in seawater2 dissolved (approx. 0.01% by mass).
In terms of quantity, the major part of the carbon is stored in the rock shell (lithosphere). All other deposits make up only about 1/1000 of the total carbon in terms of quantity.
Modifications of carbon
Elemental carbon is non-metallic and occurs in several allotropic modifications: diamond, graphite, fullerenes, carbon nanotubes, ADNR. Macroscopically, the properties are very different and almost contradicting each other.
Graphite is a good electrical conductor and is deep black in color. Its conductivity is anisotropic: very good along the crystal planes and poorly perpendicular to the planes. It is easy to split and serves as a lubricant. Diamond, on the other hand, is a very good insulator and is transparent. Diamond is also the hardest known natural material and is used as an abrasive. All carbon-based materials can be traced back to these two basic types (see below).
Atomic model of carbon
The model of atomic and molecular orbitals illustrates how the different manifestations of carbon come about.
Carbon has six electrons. According to the shell model, two electrons occupy the inner one 1s-Bowl. The 2s-Level of the second shell also takes two electrons, two more that 2px- and 2py- Level. Only the four outer electrons of the second shell appear chemically. The probability of the electrons being in one s-Level is spherical. In one p-Level it is anisotropic. The electrons populate a teardrop-shaped space, one drop each to the left and right of the center along the x-axis, if one imagines the atom placed in the center of a Cartesian coordinate system. These are perpendicular to it py- and pz-Orbital.
Diamond (sp3) Structure
The 2sLevel can be matched with the 3rd 2p-Levels hybridize and 4 energetically equivalent sp³-Orbitals form. This can be explained clearly in such a way that one of the s electrons is lifted into the previously empty p orbital and the orbital energies are equalized in the process. These orbitals have an elongated, asymmetrical teardrop shape. Were the forms of p-Orbitals arranged mirror-symmetrically to the center point, they now appear like a club elongated in one direction. The picture shows the main lobes, the side lobes have been left out for the sake of clarity. The four sp³-Orbitals are oriented symmetrically in space with the greatest possible distance from one another, they point into the corners of an imaginary tetrahedron.
Do the sp³-Orbitals of atoms, they can form firm covalent bonds, which then reflect the tetrahedral structure. They form the basic structure of the diamond lattice (see crystal structure there.)
Graphite (sp2) Structure
Are only 2 of the 3 p-Orbitals involved in the hybridization, the so-called arise sp²-Orbitals. The sp²- Orbitals are perpendicular to the leftover p-Orbital off. For example, this is p-Orbital perpendicular to the x-y plane, the sp²- Orbitals symmetrical in the x-y plane. They have the same angle of 120 ° to each other. The picture on the left illustrates the situation. The unhybridized p-Orbital is omitted for the sake of clarity.
sp²-Carbon atoms can form covalent bonds with one another, which then lie in one plane. Their structure is hexagonal, i.e. the basic structure of the planar planes of graphite (see crystal lattice structure there). The remaining p-Orbitals also interact with each other. You shape them pi-Bonds with significantly lower binding energies than the sigma-Bonds of the sp² respectively sp³-Orbitals.
Chemically we speak of a double bond. The spelling C = C neglects the different character of both bonds.
The binding energy of the diamond-like tetrahedral sp³-Single bond 'C-C' is 350 kJ / mol, that of the graphite-like hexagonal sp²- double bond C = C only 260 kJ / mol higher.
The stabilizes itself in a carbon ring with six carbon atoms pi-Binding through delocalization of the electrons within the ring (for more on this see
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