Physical and Chemical Properties of Carbon

Carbon is a chemical element that is non-metallic. Its symbol is 'C'. Its atomic number is 6. It belongs to group 14 in the periodic table. Carbon is mainly found in coal deposits; however, the carbon obtained from coal deposits must be processed for its commercial use.

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Carbon is one of the most significant elements on Earth. It is also a major constituent of most organic compounds. Since all the living bodies on Earth are made of mostly organic compounds, they (indirectly, carbon and its compounds) become important for our existence. The human body constitutes about 18% of carbon. Apart from this, carbon has its utility in various domains of technology, also such as in pieces of jewellery, paints, synthetic fibres, production of steel and carbon dating, etc.

Physical Properties and Allotropes of Carbon

The atoms of carbon can be bonded in different ways. They form allotropes of carbon. Allotropes are a different form of an element with a difference in physical properties but a similarity in chemical properties. It occurs in the same physical state in two or more crystalline forms. The most popular among the three allotropes of carbon are graphite and diamond. They both have different crystalline structures.

Differences between Graphite and Diamond:

• Graphite: It has three covalent bonds around one carbon atom. It has a planar structure. It is composed of an sp2 hybridised carbon atom. It has a relative density of 2.3. It is black in colour and opaque. It is a good conductor of electricity. It is a very good lubricant and the softest material known and greasy to touch. Certain forms of graphite are used in thermal insulation and certain others in thermal conduction. It burns in air at 700–800oC to give carbon dioxide. It is insoluble in all ordinary solvents.

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• Diamond: It occurs naturally in a free state. It is a very stable allotrope of carbon made up of four covalent bonds around one carbon atom. It has a face-centred cubic crystal structure. It is composed of sp3 hybridised carbon atoms. It is transparent and has a high relative density. It also has a high refractive index of 2.45. It is a non-conductor of heat and electricity. Diamond is the hardest natural mineral found until now. It burns in the air at 900oC to give carbon dioxide. It is insoluble in all solvents.

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Both graphite and diamond occur in the solid state. They are both very brittle. The density of different forms of carbon depends upon their respective origin. There is some form of carbon that is pure like coal and some which may not be pure and are mixtures of hydrogen and carbon.

The third allotrope and the purest form of carbon are 'Fullerene’. They have the potential to function as a semiconductor, conductors, and superconductors under certain conditions. They can also change light transmission based on intensity and this is referred to as a photometric effect. They are safe and inert. They also create active derivatives.

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Chemical Properties of Carbon

Chemical properties determine how carbon will react with other substances or change from one form to the other. The chemical properties of carbon are observed during the chemical reactions. Carbon forms millions of compounds.

Carbon takes part in four main reactions:

1. Combustion Reaction: When carbon burns in air, it gives carbon dioxide, heat, and light. Combustion is referred to as the process in which burning of carbon in excess of oxygen results in the production of heat and light.

C(s) + ½ O2(g) \[\rightarrow\] CO2(g) + heat + light

Unsaturated carbon burns with a yellow flame and produces soot while saturated carbon burns with a blue flame. Combustion could be either complete combustion or incomplete combustion.

In the complete combustion of a hydrocarbon, combustion takes place in excess of oxygen and the final products are carbon dioxide and water. Heat and light are generated in the form of energy. Saturated compounds undergo complete combustion.

On the contrary, incomplete combustion takes place when there is insufficient oxygen and there is an excess of hydrocarbon. It produces products which are carbon monoxide or carbon and water. It also has a smoky flame and produces soot. Unsaturated compounds undergo incomplete combustion.

2. Oxidation Reaction: Carbon and its compounds are oxidised in the presence of oxygen.

C(s) + ½ O2(g) \[\rightarrow\] 2CO(g)

All combustion reactions are oxidation reactions but all oxidation reactions are not combustion reactions.

3. Addition Reaction: Carbon has the ability to make long strings or chains of atoms. This is referred to as the addition reaction. Unsaturated compounds undergo this reaction to become saturated.

Example: When ethene which contains a double bond is heated in the presence of hydrogen using a nickel catalyst, it produces ethane.

CH2=CH2 + H2 + (Nickel Catalyst) \[\rightarrow\]CH3 - CH3

4. Substitution Reaction: The substitution reaction is a reaction in which a functional group in a compound is replaced by another functional group.

Example: CH3Cl + OH- \[\rightarrow\] CH3OH + Cl- 

Carbon Isotopes

1. Carbon-12 (12C): It has six neutrons and six protons. This is the most common isotope. Carbon-12 is highly stable and has a proportion of about 98.89% in a given sample. Hence, it is the major constituent of any sample of carbon.

2. Carbon-13 (13C): It has seven neutrons and six protons. This carbon isotope is also stable in nature and is heavier than the carbon-12 isotope. The proportion of carbon-13 in a given sample is about 1.11%.

3. Carbon-14 (14C): It contains eight neutrons and six protons in its nucleus. This isotope is unstable and highly radioactive. However, it decays into a stable product over time. It is heavier than carbon - 12,13 and has a very low proportion in a sample of less than about 10-10 %.

Conclusion

This was a small discussion on carbon, its physical and chemical properties, allotropes of carbon and isotopes, and their percentage occurrence in a given sample, and the importance of carbon.