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Chemistry » Chemistry 112: Organic Molecules » Organic Molecular Structures

Special Properties of Carbon

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Special properties of carbon

Carbon has a number of unique properties which influence how it behaves and how it bonds with other atoms:

• Carbon (see figure below) has four valence electrons which means that each carbon atom can form a maximum of four bonds with other atoms. Because of the number of bonds that carbon can form with other atoms, organic compounds can be very complex.

• Carbon can form bonds with other carbon atoms to form single, double or triple covalent bonds.

• Carbon can also form bonds with other atoms like hydrogen, oxygen, nitrogen and the halogens.

• Carbon can bond to form straight chain, branched, and cyclic molecules.

Carbon (a) as seen on the periodic table and (b) a Lewis dot representation.

• Because of this, long chain structures can form. This is known as catenation – the bonding of atoms of the same element into longer chains. These chains can either be unbranched (see figure below) or branched (have a branched group, see the second figure below) and can contain single carbon-carbon bonds only, or double and triple carbon-carbon bonds as well.

Unbranched carbon chains with (a) single carbon-carbon bonds, (b) single and double carbon-carbon bonds and (c) single and triple carbon-carbon bonds.

Branched carbon chains with (a) single carbon-carbon bonds, (b) single and double carbon-carbon bonds and (c) single and triple carbon-carbon bonds.

• Because of its position on the periodic table, most of the bonds that carbon forms with other atoms are covalent. Think for example of a $$\text{C}-\text{C}$$ bond. The difference in electronegativity between the two atoms is zero, so this is a pure covalent bond. In the case of a $$\text{C}-\text{H}$$ bond, the difference in electronegativity between carbon ($$\text{2.5}$$) and hydrogen ($$\text{2.2}$$) is so small that $$\text{C}-\text{H}$$ bonds are almost purely covalent. The result of this is that most organic compounds are non-polar. This affects some of the properties of organic compounds.

Sources of carbon

The main source of the carbon in organic compounds is carbon dioxide in the atmosphere. Plants use sunlight to convert carbon dioxide and water (inorganic compounds) into sugar (an organic compound) through the process of photosynthesis.

$$6\text{CO}_{2}(\text{g}) + 6\text{H}_{2}\text{O}(\text{l})$$ $$\to$$ $$\text{C}_{6}\text{H}_{12}\text{O}_{6}(\text{aq}) + 6\text{O}_{2}(\text{g})$$

Plants are therefore able to make their own organic compounds through photosynthesis, while animals feed on plants or plant products in order to gain the organic compounds that they need to survive.

Other important sources of carbon are fossil fuels such as coal, petroleum and natural gas. This is because fossil fuels are themselves formed from the decaying remains of dead organisms (refer to Grade 11 for more information on fossil fuels).