Carbon compounds can be present in our food, clothing, and even the pencil’s lead we use. It exists in both its and mixed forms. It can be found as coal or graphite in its basic form. It exists as metal carbonates, hydrocarbons, and carbon dioxide gas in its combined state. Chemical properties of Carbon Compounds form lengthy chains, branches, and close structures by forming direct bonds between atoms of the same element.

It produces a vast spectrum of compounds, from tissues to medications, combined with other elements such as dihydrogen, dioxygen, chlorine, and Sulphur. In this article, we will study some of the chemical properties of carbon compounds and the example that makes them so useful.

Before studying the chemical properties of carbon compounds, let us see what carbon is?

Carbon

Carbon is the fourth element in the periodic table’s second period, with an atomic number \(6\) and an atomic mass of \(12\). It is the sixteenth most abundant element on the planet and can be found in both the and combined states.

It is in the middle of the period and can react with atoms on both sides. This element is the foundation of a unique, organic environment due to the multitude of possible connections. The electronic configuration of carbon atom is \({\rm{1}}{{\rm{s}}^{\rm{2}}}{\rm{2}}{{\rm{s}}^{\rm{2}}}{\rm{2}}{{\rm{p}}^{\rm{2}}}\). The structure of electronic levels in compounds, on the other hand, might vary greatly.

The characteristic properties that make carbon so important are as follows-

• i. Catenation- It is the property of a self combination of carbon atoms to form long chains. It gives rise to an extremely large number of carbon compounds.
• ii. Tetravalency- A carbon has four electrons in its outermost shell, and a stable electronic configuration can be obtained by sharing those four electrons.

All carbon compounds have some characteristics in common. Below given are some of the properties of carbon compounds from a chemical approach. The following are four major chemical reactions:

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Combustion (or Burning)

The process of burning a carbon compound in the air to give carbon dioxide, water, heat and light, is known as combustion.

Combustion is also called burning, and it can be of two types- complete combustion and incomplete combustion. Most of the carbon compounds burn in the air to produce a lot of heat.

i. For example, alkanes burn in air to produce a lot of heat, due to which alkanes are excellent fuels.

When methane (natural gas) burns is a sufficient supply of air, then carbon dioxide and water vapour are formed, and a lot of heat is also produced.

\({\rm{C}}{{\rm{H}}_4} + 2{{\rm{O}}_2}{\rm{(combustion)}} \to {\rm{C}}{{\rm{O}}_2} + 2{{\rm{H}}_2}{\rm{O}} + {\rm{Heat}} + {\rm{Light}}\)

Since natural gas produces a lot of heat during the reaction and does not cause much air pollution, it is used as fuel in homes, transport, and industry. Many vehicles nowadays use CNG to run.
The cooking gas (LPG) we use in our homes is mainly an alkane called butane \(\left( {{{\rm{C}}_{\rm{4}}}{{\rm{H}}_{{\rm{10}}}}} \right){\rm{.}}\)

The saturated hydrocarbons (alkanes) generally burn in the air with a blue, non-sooty flame. This is because the percentage of carbon in saturated hydrocarbons is comparatively low, which gets oxidised completely by the oxygen present in the air. If the supply of air for burning gets limited, then incomplete combustion of saturated hydrocarbons will take place, and they will burn by producing a sooty flame.

Therefore, the gas stove used in our homes is provided with tiny holes or inlets for the air so that sufficient oxygen/air is available for the complete burning of the fuel to produce a smokeless blue flame.

ii. For example, the unsaturated hydrocarbons (alkenes and alkynes) burn in the air with a yellow, sooty flame. This is because the percentage of carbon in unsaturated hydrocarbons is comparatively higher, which does not get oxidised completely in the air or oxygen.

Incomplete combustion of alkene

\({{\rm{C}}_2}{{\rm{H}}_4} + 2{{\rm{O}}_2}{\rm{(limited\, oxygen)}} \to 2{\rm{CO}} + 2{{\rm{H}}_2}{\rm{O}} + {\rm{sooty\, flame}}\)

But if unsaturated hydrocarbons are burned in pure oxygen, then they will burn completely, producing a blue flame.

Complete combustion of alkene

\({{\rm{C}}_2}{{\rm{H}}_4} + 3{{\rm{O}}_2}{\rm{(combustion)}} \to 2{\rm{C}}{{\rm{O}}_2} + 2{{\rm{H}}_2}{\rm{O}} + {\rm{Blue\, flame}}\)

iii. For example, ethanol or ethyl alcohol is a highly combustible and volatile liquid. When a flame is brought into contact, it immediately catches fire and burns with a blue flame.

\({{\rm{C}}_2}{{\rm{H}}_5}{\rm{OH}} + 3{{\rm{O}}_2} \to 2{\rm{C}}{{\rm{O}}_2} + 3{{\rm{H}}_2}{\rm{O}}\)

Oxidation Reaction

The addition of oxygen to a molecule or the removal of hydrogen from a molecule is called oxidation. 

This reaction can cause a compound’s functional group to shift. Although combustion is an oxidation reaction in general, not all oxidation reactions are combustion reactions.

When alcohols are oxidised in the presence of oxidising agents like alkaline potassium permanganate \(\left( {{\rm{KMn}}{{\rm{O}}_4}} \right)\) carboxylic acid is formed.
For example, ethanol forms an aldehyde (ethanal) when oxidised in the presence of an oxidising agent.

\({{\rm{C}}_2}{{\rm{H}}_5}{\rm{OH}} + [{\rm{O}}] \to {\rm{C}}{{\rm{H}}_3}{\rm{CHO}} + {{\rm{H}}_2}{\rm{O}}\)

Ethanal will be converted to ethanoic acid as the oxidation process continues in the presence of alkaline potassium permanganate \(\left( {{\rm{KMn}}{{\rm{O}}_4}} \right)\).

\({\rm{C}}{{\rm{H}}_3}{\rm{CHO}} + [{\rm{O}}] \to {\rm{C}}{{\rm{H}}_3}{\rm{COOH}}\)

Addition Reaction

Addition reactions are the characteristic property of unsaturated hydrocarbons, and it can be defined as-

The reaction in which an unsaturated hydrocarbon combines with another substance to give a single product is called an addition reaction. 

In these reactions, the attacking species adds to the molecule of unsaturated hydrocarbons, which gets converted to saturated hydrocarbons.

For example,

i. Addition of Hydrogen

The addition of hydrogen to an unsaturated hydrocarbon to obtain a saturated hydrocarbon is called hydrogenation. This process takes place in the presence of nickel or palladium metals as a catalyst.

This process of hydrogenation is used to prepare vegetable ghee from vegetable oils.

The vegetable oils or cooking oils are unsaturated in the sense that their molecules contain at least one double bond in their structure. Upon passing hydrogen gas through the oil in the presence of a nickel catalyst, the double bond changes to a single bond. Vegetable ghees such as Dalda is an example of this process.

ii. Addition of Halogens

Halogens such as chlorine and bromine also give addition reactions with unsaturated hydrocarbons.

The addition of bromine is particularly important because it is used as a test for unsaturated compounds. For this purpose, bromine is used in the form of bromine water that has a red-brown colour due to the presence of bromine in it. When bromine water is mixed with an unsaturated compound, then bromine gets added to the unsaturated compound, and the red-brown colour of the bromine water is discharged, and it becomes colourless. 

Thus, all unsaturated compounds decolourise bromine water, but saturated compounds do not.

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Substitution Reaction

A substitution reaction occurs when one atom or a group of atoms in a compound is replaced by another atom (or group of atoms). Single displacement reactions are known as substitution reactions.

Saturated hydrocarbons are quite unreactive because they contain only a carbon-carbon single bond. Being unreactive, saturated hydrocarbons do not react with many substances, but they undergo substitution reactions.

In the substitution reaction of alkane, one or more hydrogen atoms of a hydrocarbon are replaced by some other atoms. If the substitution takes place by chlorine, it is called chlorination. This reaction takes place in the presence of sunlight.

For example, methane reacts with chlorine in the presence of sunlight to form chloromethane and hydrogen chloride.

\({\rm{C}}{{\rm{H}}_4} + {\rm{C}}{{\rm{l}}_2}{\rm{(sunlight)}} \to {\rm{C}}{{\rm{H}}_3}{\rm{Cl}} + {\rm{HCl}}\)

Substitution by bromine and iodine atoms can be carried out in the same manner. The chemical reactions carried in the presence of sunlight are called photochemical reactions.

Summary

In this article, we studied in detail about the four important chemical reactions that carbon compounds undergo. We also studied that bromine water can be used to distinguish between saturated and unsaturated compounds and why the gas stove burners are provided with tiny holes. Now we know that hydrogenation of vegetable oils results in the formation of vegetable ghee.

Point to remember: The colour of the flames tells us whether there is complete combustion or incomplete combustion of substance taking place.

FAQs

Q.1. What are the chemical properties of carbon compounds?
Ans: The following are four major chemical properties that mostly carbon compounds possess:
i. Combustion or burning
ii. Oxidation reaction
iii. Addition reactions
iv. Substitution reaction

Q.2. Why does the bottom of some vessels get blackened after some time?
Ans: The bottoms of vessels can sometimes become darkened due to the limited supply of air or oxygen, leading to incomplete combustion caused by a clog in the burner’s nozzle. 

Q.3. Why do the burners of gas stoves have small holes or inlets?
Ans: The gas stove used in our homes is provided with tiny holes or inlets for the air so that sufficient oxygen/air is available for the complete burning of the fuel to produce a smokeless blue flame.

Q.4. How can saturated and unsaturated hydrocarbon compounds be differentiated using a chemical property?
Ans: The saturated and unsaturated hydrocarbon compounds can be differentiated by using bromine water. If the substance is unsaturated, it will decolourise the red-brown colour of bromine water, and if it is a saturated compound, it will have no effect.

Q.5. What do you understand about the substitution reaction of carbon compounds?
Ans: In the substitution reaction of alkane, one or more hydrogen atoms of a hydrocarbon are replaced by some other atoms. If the substitution takes place by chlorine, it is called chlorination. This reaction takes place in the presence of sunlight.

Q.6. An addition reaction takes place in which hydrocarbon-saturated or unsaturated?
Ans: Addition reaction takes place in unsaturated hydrocarbons, whereas substitution reaction takes place in saturated hydrocarbons.