Physical and Chemical Properties of Carbon

What is Carbon? Properties of Carbon and Isotopes

WHAT IS CARBON?

Carbon is a chemical element which 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 the coal deposits, however, the carbon obtained from coal deposits must be processed for its commercial use.



CARBON ISOTOPES

1) CARBON-12(12C) ---> it has six neutrons and six protons. This is the most common isotope.
2) CARBON-13(13C) ----> it has seven neutrons. It is the heaviest isotope after 12C.
3) CARBON-14(14C) ----->It contains eight neutrons in its nucleus. This isotope is unstable and highly radioactive. 
However, it will decay into a stable product over time.

PHYSICAL PROPERTIES 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 similarity in chemical properties. It occurs in the same physical state in two or more crystalline forms. The most popular among these 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 a sp2 hybridized carbon atom. It has a relative density of 2.3. It is black in color and opaque. It is a good conductor of electricity. It is a very good lubricant and the softest materials 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.

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-centered cubic crystal structure. It is composed of sp3 hybridized 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 air at 900oC to give carbon dioxide. It is insoluble in all solvents.

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 which is pure like coal and some which may not be pure and are mixtures of hydrogen and carbon.

The purest form of carbon is 'Fullerene’. They have the potential to function as a semiconductor, conductor, and superconductor 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.

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 the production of heat and light.

C (s) + O2 (g) -----> 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 Smokey flame and produces soot. Unsaturated compounds undergo incomplete combustion.

2) OXIDATION REACTION:

Carbon and its compounds are oxidized in the presence of oxygen.

C (s) + O2 (g) ------> 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 double bond is heated in the presence of hydrogen using nickel catalyst, it produces ethane.
                   CH2=CH2 + H2+ (Nickel catalyst) ⇨ 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- ----> CH3OH + Cl-