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Carbon and its Compounds

Chapter: Carbon and its Compounds

Introduction

Carbon is termed to be an element of enormous importance to us in both elemental and combined form. Food, clothes, medicines, books, and many of the things are based on this element carbon. Also all the living structures are carbon based.  Only 0.02% carbon is found in earth’s crust. Carbon is found in minerals like hydrogen carbonates, carbonates, coal and petroleum. 0.03% of carbon dioxide is present in the atmosphere. Though it is available in very small amount, its importance is very large.

Bonding in Carbon – The Covalent Bond:

Most of the carbon compounds are found to be poor conductors of electricity. Carbon compounds have covalent bonds between them. Covalent bond is a bond that is formed by sharing an electron pair between two atoms.  Carbon compounds behave as poor conductors of electricity because of the presence of covalent bond between them. Carbon atoms form covalent bonds between themselves and with the atoms of other elements also.

Allotropes of Carbon

Allotropy is defined as the property of some chemical elements to exist in two or more different forms. The two different allotropes of carbon are diamond and graphite. In diamond, each carbon atom is bonded to other four carbon atoms forming a rigid 3-dimensional structure while in the case of graphite each carbon atom is bonded to other three carbon atoms in the same plane giving a hexagonal array.Fullerene is also an allotrope of carbon containing clusters of 60 carbons joined together to form a sphere (similar to the football) and this allotrope is also called as buckminsterfullerene.

 

 

Nature of Carbon

The covalent bond enables carbon to form a large number of compounds. Two major factors noticed in the case of carbon are –

1 - Carbon has the distinctive capability to form bonds with other atoms of carbon thus giving rise to more large molecules. This property is called as catenation. Carbon may be present as long chains, branched chains or sometimes arranged in rings in these compounds. Carbon compounds show the property of catenation to such an extent that is not shown in any other elements. The carbon-carbon bond is very strong and hence it is stable. This gives us the large number of compounds with many carbon atoms linked to each other.

2 - Carbon has a valency of four. Carbon is capable of bonding with four other atoms of carbon or atoms of some other mono-valent element. Compounds of carbon are formed with oxygen, hydrogen, nitrogen, sulphur, chlorine and many other elements giving rise to compounds with specific properties which depend on the elements other than carbon present in the molecule.

Saturated and Unsaturated Carbon Compounds

Carbon atoms may be connected by single, double or triple bonds. Saturated compounds are such compounds which are linked by single bonds between the carbon atoms. Carbon Compounds having double or triple bonds between their carbon atoms are called unsaturated compounds.

Let us consider example of methane, which is a compound of carbon. Methane is extensively used as a fuel and is a key component of bio-gas and Compressed Natural Gas (CNG). It is also one of the simplest compounds formed by carbon. Methane has a formula CH4. It is formed by bonding between carbon and hydrogen. Ethane is another compound formed this way.

 

 

Nomenclature of Carbon Compounds

The names of compounds in a homologous series are based on the name of the basic carbon chain modified by a “prefix” “phrase before” or “suffix” “phrase after” indicating the nature of the functional group.

The following method is used to name a carbon compound:

1 - Categorize the number of carbon atoms in the compound. A compound having three carbon atoms would have the name propane

2 - It is indicated in the name of the compound with either a prefix or a suffix in case if a functional group is present.

3 - If the name of the functional group is to be given as a suffix, the name of the carbon chain is modified by deleting the final ‘e’ and adding the appropriate suffix.

4 - The final ‘ane’ in the name of the carbon chain is substituted by ‘ene’ or ‘yne’, if the carbon chain is unsaturated,

Chemical Properties of Carbon Compounds

The different chemical properties of carbon compounds are

1 . Combustion

Combustion is the process of carbon burning in the presence of oxygen and releases light and heat.

C + O2 → CO2 + heat and light

Saturated hydrocarbons will give a clean flame when burnt and unsaturated carbons give yellow flame with black smoke.

2 . Oxidation

Oxidation is defined as the process when oxygen combines with an element, changing the appearance of the element. Carbon compounds can be easily oxidised on combustion.

The substances which are capable of adding oxygen to others are known as oxidizing agents

3 . Addition Reaction

Hydrogen is added to unsaturated hydrocarbons in the presence of catalysts like nickel or palladium to form saturated hydrocarbons. Catalysts are defined as substances which allow a reaction to happen at a different rate without the reaction getting affected itself. Hydrogenation of vegetable oils is such a reaction and nickel is used as a catalyst.

4 . Substitution Reaction

Substitution reaction is a reaction in which one type of atom or a group of atoms takes the place of another.

Saturated hydrocarbons are quite unreactive and also inert in the presence of most reagents. However, in the presence of sunlight, chlorine is added to hydrocarbons in a very fast reaction. Chlorine can replace the hydrogen atoms one by one.

Soaps and Detergents

Most of the dirt particles on skin or clothes are oily in nature. When a dirty cloth is put in water containing dissolved soap, the oil does not dissolve in water. The soap molecules are actually sodium and potassium salts long chain carboxylic acids. The hydrophilic part and the hydrophobic part are the two vital parts of every soap molecule. The acid end of the soap dissolves in water while its carbon chain dissolves in the oil. In this way, soap molecules form a special round type structure called micelles in which one end of the soap molecule is towards the oil droplet and the other end is towards the water. This forms an emulsion in water. The soap micelles help in removing the dirt particle from the surface and this dirt dissolves in water and hence the surface gets cleaned.