Carbon And Its Compound

Carbon is one of the most important non-metals.

Its symbol is C and its atomic number is 6.

Carbon is present in the Earth’s crust in the form of minerals and in the atmosphere as carbon dioxide.

According to the PDF:

• Carbon in Earth’s crust as minerals – 0.02%
• Carbon in atmosphere as CO₂ – 0.03%

All living things are made up of carbon or carbon-containing compounds.

Many substances used in daily life, such as soaps, detergents and medicines, are also made up of carbon compounds.

Covalent Bond In Carbon Compounds

The valency of carbon is 4.

Carbon has electronic configuration 2,4.

To become stable, carbon would need to either:

• Gain 4 electrons
• Lose 4 electrons

But both are difficult.

Why Carbon Does Not Gain 4 Electrons

Carbon cannot easily gain 4 electrons to form C⁴⁻ because this would make the ion highly unstable due to strong electron-electron repulsion.

Why Carbon Does Not Lose 4 Electrons

Carbon cannot easily lose 4 electrons to form C⁴⁺ because it would require a very high amount of energy.

Therefore, carbon achieves stability by sharing electrons.

The bonds formed by mutual sharing of electrons are called covalent bonds.

Types Of Covalent Bonds

Single Covalent Bond

A single covalent bond is formed when each atom contributes one electron.

It is represented by -.

Example:

H-F

Double Covalent Bond

A double covalent bond is formed when each atom contributes two electrons.

It is represented by =.

Example:

O=O

Triple Covalent Bond

A triple covalent bond is formed when each atom contributes three electrons.

It is represented by ≡.

Example:

N≡N

Properties Of Covalent Compounds

• Covalent bonds are formed by mutual sharing of electrons.
• Covalent compounds may be solid, liquid or gas.
• They generally have low melting and boiling points.
• They have weak intermolecular forces of attraction.
• They are poorly soluble in polar solvents like water.
• They are soluble in organic or non-polar solvents.
• They do not contain ions.
• They are bad conductors of electricity.

Allotropic Forms Of Carbon

The phenomenon in which an element exists in two or more forms having different physical properties but similar chemical properties is called allotropy.

These different forms are called allotropes.

Carbon is broadly classified into:

• Crystalline forms
• Amorphous forms

Crystalline Allotropes Of Carbon

The crystalline forms of carbon include:

• Diamond
• Graphite
• Fullerenes

These are the purest forms of carbon.

They have similar chemical properties but different physical properties because their carbon atoms are arranged differently.

Diamond

Diamond is a white transparent crystal.

The Kohinoor diamond is one of the oldest and most famous diamonds in the world.

Diamond occurs naturally and can also be synthesized by subjecting pure carbon to very high pressure and temperature.

Synthetic diamonds are generally small in size.

The size of diamonds is measured in carats.

• 1 carat = 200 mg

Structure Of Diamond

• Diamond is the hardest natural substance.
• Each carbon atom is bonded to four other carbon atoms by strong single covalent bonds.
• It forms a rigid three-dimensional structure.
• It has a tetrahedral structure.
• Bond angle is 109°28′.
• Atoms are closely packed, so density is high.
• Melting point is about 3930°C or 4203 K.
• All valence electrons are involved in bonding.
• No free electrons are present.
• Therefore, diamond is a bad conductor of electricity.

Uses Of Diamond

• Used for cutting glass.
• Used for drilling purposes.
• Used in surgical tools, such as cataract operations.
• Used in jewellery and precious gems.
• Used in making dies for drawing thin wires.

Graphite

Graphite is a greyish-black substance.

It occurs naturally with mica, quartz and silica.

It can also be prepared artificially in an electric furnace at 2273-2773 K.

Structure Of Graphite

• Each carbon atom is bonded to three other carbon atoms in the same plane.
• It forms hexagonal rings.
• It has a layered structure.
• One electron remains free or delocalized.
• Layers are held together by weak forces.
• This makes graphite soft and slippery.
• It has a two-dimensional sheet-like structure.
• Distance between layers is about 340 pm.
• Carbon atoms are less closely packed than diamond.
• Density of graphite is 2.22 g/cm³.
• Density of diamond is 3.51 g/cm³.
• Graphite is a good conductor of heat and electricity due to free electrons.

Uses Of Graphite

• Used as lubricant or graphite grease.
• Used in pencil leads after mixing with clay or wax.
• Used for making electrodes.
• Used for making crucibles because it can resist high temperature.

Diamond And Graphite: Difference

Property	Diamond	Graphite
Structure	3D tetrahedral structure	Layered 2D hexagonal structure
Bonding	Each carbon bonded to 4 atoms	Each carbon bonded to 3 atoms
Nature	Hardest natural substance	Soft and slippery
Density	High, 3.51 g/cm³	Lower, 2.22 g/cm³
Electrical conductivity	Non-conductor	Good conductor
Reason	No free electrons	Presence of free electrons
Appearance	Transparent	Black or grey opaque

Fullerenes

Fullerenes are a new family of carbon allotropes.

They are spheroidal in shape and contain even numbers of carbon atoms ranging from 60 to 350 or more.

C₆₀ fullerene is the most stable form.

In C₆₀

• 60 carbon atoms are arranged like a soccer ball.
• It is also called a buckyball.
• It contains 20 hexagonal rings.
• It contains 12 pentagonal rings.
• Pentagons are attached only to hexagons.
• No two pentagons are fused together.

It is named Buckminster fullerene after architect Buckminster Fuller.

Unique Nature Of Carbon

Carbon forms a very large number of compounds because of its special properties.

The important reasons are:

• Catenation
• Tetravalency
• Tendency to form multiple bonds

Catenation

Catenation is the property of carbon to form long chains or rings by self-linking.

Carbon shows strong catenation because:

• Carbon atom is small in size.
• Carbon-carbon covalent bonds are strong.

Tetravalency Of Carbon

Carbon belongs to Group 14.

Its electronic configuration is 2,4.

Its valency is 4.

Because of tetravalency, carbon forms strong and stable bonds with many atoms.

This gives rise to a very large number of carbon compounds.

Tendency To Form Multiple Bonds

Carbon can form:

• Single bonds – C-C
• Double bonds – C=C
• Triple bonds – C≡C

Carbon also forms bonds with elements such as:

• Oxygen
• Nitrogen
• Sulphur

Isomerism

When compounds have the same molecular formula but different structures and properties, the phenomenon is called isomerism.

These different structures are called isomers.

Example

Pentane, C₅H₁₂, has 3 structural isomers:

• n-pentane
• iso-pentane
• neo-pentane

Organic Compounds

Compounds obtained directly or indirectly from living organisms are called organic compounds.

Examples

• Urea
• Sugar
• Oils
• Fats
• Proteins
• Dyes

The first organic compound synthesized in the laboratory was urea.

Hydrocarbons

Hydrocarbons are organic compounds containing only carbon and hydrogen.

Hydrocarbons are of two main types:

• Saturated hydrocarbons
• Unsaturated hydrocarbons

Saturated Hydrocarbons

Saturated hydrocarbons contain only single carbon-carbon bonds.

Each carbon forms four single bonds.

They are called:

• Alkanes
• Paraffins

The simplest hydrocarbon is methane, CH₄.

General Formula

CₙH₂ₙ₊₂

Example

• Ethane – C₂H₆

Saturated hydrocarbons are chemically less reactive because they contain only single bonds.

Unsaturated Hydrocarbons

Unsaturated hydrocarbons contain double or triple bonds.

Some carbon atoms are directly bonded to less than four atoms.

Unsaturated hydrocarbons are of two types:

• Alkenes
• Alkynes

Alkenes

• Contain double bond, C=C.
• General formula is CₙH₂ₙ.
• Also called olefins.

Example

• Ethene – C₂H₄
• Propene – C₃H₆

Alkynes

• Contain triple bond, C≡C.
• General formula is CₙH₂ₙ₋₂.
• Also called acetylene series.

Example

• Ethyne – C₂H₂
• Propyne – C₃H₄

Nomenclature Of Hydrocarbons

No. Of Carbon Atoms	Prefix	Alkane	Alkene	Alkyne
1	Meth	CH₄ Methane	–	–
2	Eth	C₂H₆ Ethane	C₂H₄ Ethene	C₂H₂ Ethyne
3	Prop	C₃H₈ Propane	C₃H₆ Propene	C₃H₄ Propyne
4	But	C₄H₁₀ Butane	C₄H₈ Butene	C₄H₆ Butyne
5	Pent	C₅H₁₂ Pentane	C₅H₁₀ Pentene	C₅H₈ Pentyne
6	Hex	C₆H₁₄ Hexane	C₆H₁₂ Hexene	C₆H₁₀ Hexyne
7	Hept	C₇H₁₆ Heptane	C₇H₁₄ Heptene	C₇H₁₂ Heptyne
8	Oct	C₈H₁₈ Octane	C₈H₁₆ Octene	C₈H₁₄ Octyne
9	Non	C₉H₂₀ Nonane	C₉H₁₈ Nonene	C₉H₁₆ Nonyne
10	Dec	C₁₀H₂₂ Decane	C₁₀H₂₀ Decene	C₁₀H₁₈ Decyne

Homologous Series

A homologous series is a family of organic compounds having the same functional group and similar chemical properties.

Important Points

• Members have similar chemical properties.
• They can be represented by one general formula.
• Two consecutive members differ by -CH₂ group.
• Physical properties change gradually with molecular mass.
• Melting and boiling points increase with increase in molecular mass.

Functional Groups

A functional group is an atom or group of atoms that gives characteristic chemical properties to an organic compound.

Examples From The Chapter Include

Functional Group	Class Of Compound	Example
-OH	Alcohol	Butanol
-CHO	Aldehyde	Propanal
-COOH	Carboxylic acid	Ethanoic acid
-Cl	Halo compound	Chloroethane

Important Reactions Of Carbon Compounds

Combustion

Carbon compounds burn in oxygen to form carbon dioxide and water.

Example

CH₄ + 2O₂ → CO₂ + 2H₂O

Combustion releases a large amount of heat and light.

Addition Reaction

Unsaturated hydrocarbons undergo addition reactions.

Example

Oils react with hydrogen in the presence of nickel or palladium catalyst to form fats.

This is an example of an addition reaction.

Substitution Reaction

Saturated hydrocarbons react with chlorine in the presence of sunlight.

In this reaction, hydrogen atoms are replaced by chlorine atoms.

This is called a substitution reaction.

Ethanol

Ethanol is an alcohol.

Chemical Formula

CH₃CH₂OH or C₂H₅OH

Physical Properties Of Ethanol

• Ethanol is a colourless liquid.
• It has a pleasant smell.
• Freezing point is 156 K.
• Boiling point is 351 K.
• It is soluble in water in all proportions.
• It is lighter than water.
• It has no effect on litmus solution.

Chemical Properties Of Ethanol

Combustion

Ethanol is highly inflammable.

It burns in oxygen with a pale non-luminous flame to form carbon dioxide and water.

CH₃CH₂OH + 3O₂ → 2CO₂ + 3H₂O

This is an exothermic reaction.

Reaction With Sodium Metal

Ethanol reacts with sodium metal to form sodium ethoxide and hydrogen gas.

2CH₃CH₂OH + 2Na → 2CH₃CH₂ONa + H₂

Reaction With Concentrated Sulphuric Acid

When ethanol is heated with excess concentrated sulphuric acid at 443 K, ethene is formed.

CH₃CH₂OH → CH₂=CH₂ + H₂O

Concentrated sulphuric acid acts as a dehydrating agent because it removes water from ethanol.

Reaction With Ethanoic Acid

Ethanol reacts with ethanoic acid in the presence of concentrated sulphuric acid to form ethyl ethanoate, an ester with fruity smell.

This reaction is called esterification.

Oxidation

Ethanol is oxidised to ethanoic acid in the presence of strong oxidising agents such as:

• KMnO₄
• K₂Cr₂O₇
• HNO₃

Reaction:

CH₃CH₂OH + [O] → CH₃COOH

Ethanoic Acid

Ethanoic acid is commonly known as acetic acid.

Molecular Formula

CH₃COOH

A 5-8% dilute solution of ethanoic acid in water is called vinegar.

Vinegar is used for preserving:

• Food
• Sausages
• Pickles

Physical Properties Of Ethanoic Acid

• It is colourless.
• It has a sharp pungent vinegar-like smell.
• It is corrosive.
• It has sour taste.
• Boiling point is 391 K.
• It is miscible with water, alcohol and ether in all proportions.
• Melting point is 290 K.

Ethanoic acid freezes during winter in cold climates, so it is called glacial acetic acid.

Chemical Properties Of Ethanoic Acid

Acidic Nature

Ethanoic acid is acidic and turns blue litmus red.

Reaction With Metals

Ethanoic acid reacts with sodium to form sodium ethanoate and hydrogen gas.

2CH₃COOH + 2Na → 2CH₃COONa + H₂

Reaction With Alkalies

Ethanoic acid reacts with sodium hydroxide to form sodium ethanoate and water.

CH₃COOH + NaOH → CH₃COONa + H₂O

Reaction With Bicarbonates And Carbonates

Ethanoic acid reacts with sodium bicarbonate to form sodium ethanoate, carbon dioxide and water.

CH₃COOH + NaHCO₃ → CH₃COONa + CO₂ + H₂O

It also reacts with sodium carbonate:

2CH₃COOH + Na₂CO₃ → 2CH₃COONa + CO₂ + H₂O

Reaction With Alcohols

Ethanoic acid reacts with alcohols in the presence of concentrated sulphuric acid to form an ester.

CH₃COOH + C₂H₅OH → CH₃COOC₂H₅ + H₂O

This reaction is called esterification.

Saponification

When an ester is treated with acid or alkali, it is converted back into alcohol and the salt of the acid.

Example:

CH₃COOC₂H₅ + NaOH → CH₃COONa + C₂H₅OH

This reaction is called saponification reaction.

Soap Molecules And Micelles

A soap molecule has:

• Hydrophilic head
• Hydrophobic tail

In Soap Micelles

• The ionic end of soap remains on the surface of the cluster.
• The carbon chain remains in the interior of the cluster.

This helps soap remove oily dirt from surfaces.

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