Chemical Properties of Carbon Compounds

Carbon is a very different and surprising element. The symbol of carbon is 'C' while its atomic number is 6. It is a non-metallic tetravalent element. The electronic configuration of carbon in K and L shells is 2,4. So, it has four valence electrons. Therefore, its valency is also 4, so it enters into covalent bonding with other elements by sharing electrons.  Having a valency of four, carbon is one of the most versatile elements. Carbon has a unique property of direct bonding between atoms of the same element to form long chains, to form branches, or to form close structures. This property is known as catenation. No wonder, it can form an almost infinite number of compounds, most of which are chemically organic in nature. 

These special properties and behaviour exhibited by carbon, coupled with the fact that it can form an infinite number of compounds led to the emergence of a different branch of chemistry, called organic chemistry. 

However, the reactions that these compounds undergo are limited. Some important reactions are discussed here.

Combustion (Burning of Carbon Compound in Air)

Carbon and its compounds burn in the presence of oxygen or air to give carbon dioxide, water vapours, and energy. This process of burning carbon compounds in excess of oxygen to give heat and light is called a combustion reaction.

Example:-

1)  C + O2 ---------> CO2 + Energy

2)  C2H5OH + 3O2 ----------> CO2 + 3H2O + Energy

3)  CH4 + O2 ----------> CO2 + H2O + Energy

Most carbon compounds are good fuels. Due to combustion in the presence of oxygen, we will get a clean bluish flame with saturated hydrocarbons. This will be in the case of complete combustion. If there is an incomplete combustion of saturated hydrocarbons due to lack of oxygen, a sooty flame will be observed. On the other hand, we will get a yellow flame with smoke in the case of unsaturated hydrocarbons. The important point to be noted here is that complete combustion of carbon compounds yields CO2 gas as the product. However, in the case of incomplete combustion, CO (carbon monoxide) is formed. CO is a poisonous gas that has a great affinity to haemoglobin in the blood. It combines with haemoglobin to form a compound called carboxyhemoglobin. It prevents oxygen from reaching the body cells. This condition is fatal and can lead to the death of a person, also known as carbon monoxide poisoning. 

Oxidation (Addition of Oxygen)

Oxidation can be defined as the addition of oxygen to a molecule or the removal of hydrogen from a molecule. This can change the particular functional group of a compound. Combustion is generally an oxidation reaction, but all oxidation reactions are not combustion reactions. Oxidation of alcohols produces carboxylic acid in the presence of oxidizing agents.

For Example: Ethanol, on oxidation in the presence of an oxidising agent will form ethanal (an aldehyde). As the oxidation continues, ethanal will get changed to ethanoic acid. 

What is an Oxidizing Agent?

An oxidizing agent is a substance that oxidizes other substances(adds oxygen to or removes hydrogen from other compounds) while itself getting reduced. Potassium permanganate and acidified potassium dichromate are examples of strong oxidizing agents. 

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Addition Reaction 

Unsaturated organic compounds [containing multiple bonds(=,≡)] react with hydrogen to form saturated organic compounds in the presence of catalysts. This is known as the addition reaction.

CH2=CH2 + H2  ------> CH3- CH3

 (ethene)                           (ethane)


For Example:-

Hydrogenation of vegetable oils is a process in which hydrogen is added to unsaturated oils and gives fats(saturated) in the presence of Ni as a catalyst.  Although oil, being unsaturated is better for health than fat but the disadvantage is that it cannot be preserved for a long time.

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Substitution Reaction

A reaction in which a less reactive atom or a group of atoms in an organic molecule gets replaced by another more reactive atom or group of atoms is called a substitution reaction. It is a type of single displacement reaction.

The saturated hydrocarbons are chemically least reactive. They are also called paraffins, provided the fact that they have no or little affinity towards a chemical change. Reactions of saturated hydrocarbons in the presence of sunlight with chlorine is an example of a substitution reaction.

Being a halogen, chlorine is more reactive and has the ability to displace the hydrogen atom. 

For Example - Methane reacts with chlorine in the presence of sunlight. Hydrogen atoms of methane are replaced by chlorine atoms to form methyl chloride. Also, when methyl chloride reacts with chlorine in the presence of sunlight, the same reaction goes on to form methylene chloride.

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Did You Know?

  1. Why does the bottom of some vessels gets blackened after some time? 

Sometimes, it is observed that the bottom of vessels gets blackened because of incomplete combustion of gas due to blockage in the burner's nozzle. Due to this, there is an insufficient supply of oxygen. 

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FAQ (Frequently Asked Questions)

1. What is Esterification?

Esterification is a reaction in which two reactants(an alcohol and a carboxylic acid) react together, to form a compound called ester as the reaction product. In this reaction, a.molecule of water is also eliminated. Ester is a sweet-smelling compound. It is common in organic chemistry. The general formula of the ester is RCOOR', where R and R' are alkyl groups. 

For example, when ethanoic acid reacts with ethanol, the product formed by the reaction is an ester.

CH3COOH + C2H5OH --------> CH3COOC2H5 + H2O

2. What is Polymerization?

Solution: Alkenes and alkynes at higher temperatures undergo polymerization to form bigger molecules called polymers. The repeating units which are linked and cross-linked to form long chains are called monomers. These monomers are repeated to form polymers and the process is called polymerization. 

This process is extensively used in the manufacturing of plastics and synthetic fibres.

Example:

Ethene at 400 °C undergoes polymerization to form polyethene.

nCH2 = CH2 → [-CH2 -CH2 - CH2 - CH2-]n

The polymer is usually named by adding the word “poly” to the name of the monomer. Thus, the polymer of ethene is named polyethene or polythene. Similarly, styrene is the monomer of polystyrene.