Carbon and its Compounds : CBSE Class 10 Science Notes of Chapter 4

 

Compound

Two or more elements combine to form a compound. There are two types of compounds- Organic compounds and Inorganic compounds. Organic compounds are the ones that are made up of carbon and hydrogen.

 Covalent Bond

The bond formed by sharing a pair of electrons between two atoms is known as Covalent Bond. Carbon forms covalent bonds. Carbon exists in two forms- as a free state and as a combined state. Freeform of carbon is found in graphite, diamond and fullerene. In the combined state, carbon exists as Carbon-dioxide, Glucose, Sugar etc.

Allotropes of Carbon

Different forms of an element that have the same chemical properties but different physical properties are known as Allotropes. There are three allotropes of carbon- diamond, graphite and fullerene.

Diamond

Diamond exists as a three-dimensional network with strong carbon-carbon covalent bonds. Diamonds are hard in nature with high melting points. It shines in the presence of light and it is a bad conductor of electricity. The most common use of diamonds is in making jewellery. It is also used in cutting and drilling tools.

Graphite

Graphite is made from weak Van der Waal forces. Each carbon atom is bonded with the other three carbon atoms to form hexagonal rings. It serves as a good conductor of heat and electricity. It is used as a dry lubricant for machine parts as well as it is used in lead pencils.

Fullerene

It is a hollow cage that exists in the form of a sphere. Its structure is similar to fullerene. But along with hexagonal rings, sometimes pentagonal or heptagonal rings are also present.

Fig.1 Structure of fullerene

Two Important Properties of Carbon

Catenation and tetravalency are the two important properties of carbon. Catenation is a property of carbon by which carbon atoms can link one another via the covalent bonds and can form long chains, closed rings or branched chains etc. Carbon atoms can be linked by single, double or triple bonds. Carbon has a valency of 4 due to which it is known to have tetravalency. Due to this one carbon atom can bond with other 4 carbon atoms, with other atoms also such as Oxygen, Nitrogen etc.

Hydrocarbons

Compounds that are made up of carbon and hydrogen are known as Hydrocarbons. There are two types of hydrocarbons found – Saturated Hydrocarbons and Unsaturated Hydrocarbons. Saturated Hydrocarbons consist of single bonds between the carbon atoms. For Example, Alkanes. Alkanes are saturated hydrocarbons represented by a formula, CnH2n+2.

Unsaturated Hydrocarbons are the ones with double or triple bonds between the carbon atoms. For Example, Alkenes and Alkynes. Alkenes are represented as CnH2n whereas alkynes are represented as CnH2n-2. Some saturated hydrocarbons and unsaturated hydrocarbons are represented as –

Fig.2. Saturated hydrocarbons

Fig. 3. Unsaturated hydrocarbons

The structure of hydrocarbons can be represented in the form of electron dot structure as well as open structures as shown below-

Fig.4. Electron dot structure and open structure of ethane

Fig.5. Electron dot structure and open structure of ethyne

Carbons Compounds based on the structure

Carbon Compounds can be classified as straight-chain compounds, branched-chain compounds and cyclic compounds. They are represented as –

Fig.6. Straight chain carbon compound

Fig.7. Branched-chain compounds

Fig.8. Cyclic carbon compounds

Functional Groups

One of the hydrogen atoms in hydrocarbons can be replaced by other atoms according to their valencies. The atoms which decide the properties of the carbon atoms are known as Functional Groups. For Example, Cl, Br, -OH, Aldehyde, Ketone, Carboxylic Acid etc.

Homologous Series

Series of compounds in which the same functional group substitutes for the hydrogen atom in a chain of carbon.

Fig.9. Homologous series

Nomenclature of Carbon Compounds

• First of all, identify the number of carbon atoms in compounds. And in it identify the longest chain
• Then the functional group can be indicated by suffix or prefix.
• Cyclic hydrocarbon is designated by the prefix cyclo.
• If there are two or more different substituents they are listed in alphabetical order
• If the same substituent occurs more than once, the location of each point on which the substituent occurs is given

Fig.10. Different functional groups

Chemical Properties of Carbon Compounds

Combustion

Carbon along with its compound is used as a fuel as it burns in presence of oxygen to release energy. Saturated hydrocarbons produce blue and non-sooty flame whereas unsaturated hydrocarbons produce a yellow sooty flame.

CH4 + 2O2 → CO2 + 2H2O

Oxidation

Alcohol can be oxidised to aldehydes whereas aldehydes, in turn, can be oxidised to carboxylic acid. Oxidising agents such as potassium permanganate can be used for oxidation.

Addition Reaction

Hydrogenation of vegetable oil is an example of an additional reaction. Addition of hydrogen in presence of catalysts such as nickel or palladium. This converts the oil into ghee.

Substitution Reaction

When one atom in hydrocarbon is replaced by chlorine, bromine, etc. this is known as a Substitution Reaction.

Important Carbon Compounds: Ethanol and Ethanoic Acid

Ethanol is a volatile liquid with a low melting point. It reacts with sodium to form sodium ethoxide.

This reaction is used to test the presence of ethanol by the evolution of hydrogen gas.

Dehydration of ethanol in presence of hot sulphuric acid forms alkene.

Ethanoic acid is a colourless liquid. When pure ethanoic acid freezes like ice, it is known as Glacial Acetic Acid.  It is formed at a temperature of about 16.6 degrees centigrade

Ethanoic Acid/Acetic acid when reacts with ethanol forms an ester. Ester can be identified by its sweet smell.

The reaction of esters with a strong base is used to form soap. This is known as Saponification. Acetic acid also reacts with a strong base to form sodium acetate and water.

NaOH + CH3­COOH + CH3COONa + H2O

Soaps and Detergents

Sodium or potassium salt of a carboxylic acid is known as Soap. They work most effectively in soap water. Detergents are sulphonate or ammonium salt of a long chain of carboxylic acid. They can work effectively on soft as well as hard water.

Cleansing Action of Soaps and Detergents

The cleansing action of soaps and detergents is due to the ability to minimise the surface tension of water, to emulsify oil or grease and hold them in a suspension of water. When soap dissolves in water, it forms soap anions and soap cations. The hydrophobic part of soaps and detergents are soluble in grease and the hydrophilic part is soluble in water.

Soap and Micelle Formation

When dirt and grease are mixed with soap water, soap molecules arrange them in tiny clusters known as Micelle. The hydrophilic part sticks to the water and forms the outer surface of the micelle and the hydrophobic part binds to oil and grease.