Carbon and Its Significance

Carbon and bonding Carbon is classified as a non-metal. It is the first member of group IV of the periodic table and is located in period 2 between boron and nitrogen. The carbon atom has 6 electrons and therefore has an electron configuration is 2, 4. This means it can either lose 4 electrons or gain 4 electrons to gain a stable electron configuration. It usually however tends to covalent bond with other non-metals such as hydrogen and oxygen. Since it has 4 valence (free) electrons, each carbon atom can be bonded with 4 hydrogen atoms, or 2 oxygen atoms. Carbon atoms can therefore bind to form many compounds including hydrocarbons and carbohydrates. For this reason it a useful base for the compounds of life. The large number of compounds is due to its ability to form bonds with many elements, which can be single, double or triple bonds. Carbon can from single bonds such as those in alkanes, double bonds such as those in alkenes, or triple bonds such as those is present in alkynes. Carbon also bonds with itself to produce different allotropes.

Allotropes of carbon Allotropes are forms of one element in the same physical state which have distinctly different physical properties i.e. colour, density, hardness and electrical conductivity). Diamond and graphite are some of the allotropes of carbon. Other elements which display allotropy are arsenic, phosphorus, selenium, sulfur, tin and oxygen. Allotropes have different properties because the atoms are joined or packed together in different ways to form molecules or crystals.

Amorphous carbon 

Amorphous carbon (soot) is a low pressure form of carbon that usually exists in the form of as imperfect tetrahedron structures. Each carbon is surrounded by 4 other carbons bonded to it with single bonds.

Diamond 

The carbon atoms in diamond are covalently bonded to four other carbon atoms to form a 3D covalent lattice, with the shape around each carbon atom being tetrahedral. The 6 membered rings are buckled not flat.

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All valence electrons are tied up in strong covalent bonds, so there are no mobile electrons. Thus it doesn’t conduct electricity.

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It has an orderly arrangement of atoms throughout the whole crystal gives its transparency and brilliance. For this reason it is used in jewellery.

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Diamond is a hard substance because of the strong forces between molecules and it used therefore for drills and saws.

Graphite 

Each carbon atom in graphite is bonded only to three other carbon atoms, forming a planar structure of flat six-membered rings.

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This leaves each carbon atom with 1 free valence electrons which forms a delocalised electron cloud located between the layers (called aromaticity), similar to that present in metals.

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These electrons are able to move within sheets. As a result, graphite is able to conduct electricity. However, it can cause a temporary dipole in one sheet which by electrical induction will cause a dipole of the opposite charge to occur in a neighbouring sheet. For these reasons, it is used for the electrodes in dry cell batteries and superconductors.

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In graphite, weak intermolecular forces between layers are present, resulting in these layers being able to readily sheer off or to slide over one another. For these reasons, it is used for pencils, and also as a dry lubricant.

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Graphite lubrication abilities are hypothesised to be due to the presence of a fluid layer (i.e. air) between the layers (as graphite is a poor lubricant in a vacuum).

Other allotropes of carbon 

Electrical discharge between graphite electrodes in low pressure helium causes graphite to evaporate and then condense as soot. If soluble in benzene or toluene, it forms a yellow-brown substance with 60 carbon atoms that has a soccer ball structure.

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Buckminster fullerenes (bucky-balls) are 5-6 membered rings that combine to form a spherical cage. The most common has 60 carbon atoms. Other fullerenes with 70, 74 and 80 carbon atoms have also been produced. In fact, the number of carbon atoms can range from 32 to 84 carbon atoms.

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Bucky-balls have some delocalised electrons but not like graphite.

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Cage-like fullerenes may have uses as superconductors or as lubricants because of the weak intermolecular forces between their ball-shaped molecules. However since they are expensive to produce, other materials are used instead.

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Nanotubes (or bucky-tubes) are other group of fullerenes consist of molecules that have tube-like shape, that are several nanometres long.

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Nanotubes have high tensile strength, and can act as either conductors or insulators