Chemistry Form Four – Chapter One (Somalia Syllabus)

Define Hydrocarbons?

Hydrocarbons are compounds that contain carbon and hydrogen only

• Examples of Hydrocarbons are

a) methane b) propene c)pentyne

Hydrocarbons are mainly obtained from

• Natural Gas

• Coal

• Petroleum

Hydrocarbons are commonly used as

[ ] Fuels

[ ] Candle wax

[ ] Oil

[ ] gasoline

[ ] liquid propane(LP)

Hydrocarbons are also the raw materials in the synthesis of many different consumer products

including?

1. Fabrics

2. Soaps

3. Dyes

4. Cosmetics

5. Drugs

6. Plastic

7. Rubber

Classification of Hydrocarbons?

• On the basis of bond hydrocarbons are classified into

• On the basis of structure, hydrocarbons are classified into

• On the basis of their sources and properties, hydrocarbons are classified into

On the basis of bond hydrocarbons are classified into:

1. Saturated

2. Unsaturated

On the basis of structure, hydrocarbons are classified into

1. Cyclic hydrocarbons

2. Acyclic hydrocarbons

On the basis of their sources and properties, hydrocarbons are classified into

1. Aliphatic hydrocarbon

2. Aromatic hydrocarbons

What is Saturated hydrocarbon?

• These are hydrocarbons that contain only C-C single bond

Saturated hydrocarbons are also called me

alkanes

What is unsaturated hydrocarbons?

• These are hydrocarbons that contain carbon- carbon multiple bonds(double or triple bond)

Unsaturated hydrocarbons are further divided into

a) Alkenes

b) Alkynes

c) Aromatic hydrocarbons

What isCyclic hydrocarbons?

These are closed or ring structure hydrocarbons .

Cyclic hydrocarbons are subdivide into

(I) Alicyclic hydrocarbons,which further divided into (ii) Aromatic hydrocarbons, which is further

divided into

a)cyclo-alkanes: closed structure alkanes

b) cyclo-alkenes: closed structure Alkenes

c) cyclo-alkynes: closed structure Alkynes

• Aromatic hydrocarbons, which is further divided into

a)Benzenoid: Aromatic hydrocarbons that contain benzene ring

b)Nan-Benzenoid: Aromatic hydrocarbons that do not contain benzene ring

What is Acyclic hydrocarbons?

These are open chain structure hydrocarbons, and they are also called aliphatic hydrocarbon.

They are sub-divide into

(I) Alkanes

(ii) Alkenes

(iii) Alkynes

What is Aliphatic hydrocarbon?

These are hydrocarbons derived by chemical degradation of fats or oils.

They are sub-divide into:

a) Alkane

b) Alkene

c) Alkyne

Aromatic hydrocarbons

These are hydrocarbons obtained by chemical degradation of certain pleasant smelling plant

extracts.

Define Alkane?(paraffins)

Alkanes are saturated hydrocarbons containing only carbon-carbon single bonds.

Alkanes are also called saturated hydrocarbons. because they are saturated with hydrogen

What is methane?

Methane is primary compound in natural gas.

Methane it is used to heat homes,cookfood,and power factories

1.3.1 Classification of Alkanes

Alkanes are classified into two types

1.straight chain Alanes

2.Branched chain Alanes

What is straight chain Alanes?

These are Alkanes in which each carbon atom is bonded to not more than two carbon atom.

What is Branched chain Alanes?

These are Alkanes in which at least one carbon atom is bonded to more than two other carbon

atom.

Structurally, branched chain Alanes consist of two part

• Parent chain

• Side chain

What is parent chain

This is the longest straight carbon-carbon chain of carbon atom.

Define side chain

These are short chains attached to the parent chain.

The side chain is also known as substituten or branch .

What is Alkyl groups

In organic chemistry, an alkyl group is an alkane that has one hydrogen less.

a) Normal (n)

This system is used to name straight chain Alanes.

b)Iso(I)

This system is used to name Alkanes in which one methyl group is attached to the second

carbon of the parent chain { iso-alkane}

c)Neo-(N)

This system is used to name Alkanes in which two methyl groups are attached to the second

carbon of Parent chain.[Neo-Alkanes]

IUPAC(international Union pure and applied chemistry) modified by agroup of scientist in (1958)

Isomerism in Alkanes

Isomers are defined as molecules with the same molecular formula but different structural

formula.

1.3.4 physical properties of Alkanes

1. The first four members of straight chain Alanes-- methane,ethane, propane and butane are

gases

2. [C5-C17] are liquid [C18-C........] are solids

.Alkanes do not undergo many reaction;they are called paraffins, from Latin parum affinis means

little affinity .

Alkanes reaction under certain conditions

1. Substitution

2. Combustion

What is substitution?

In a substitution reaction,One atom is displaced by another atom.

What is combustion?

Alkanes burnt in the presence of sufficient oxygen to forms carbon dioxide and water and

enormous amounts of heat energy is released.this type of combustion is known as complete

combustion.

1.3.6 General methods of preparation of Alkanes..

1. From Alkyl halides (R-X) by

2. Decarboxylation

From Alkyl halides divided into two

a)Reduction reaction

b) wurtz reaction

Decarboxylation is prepared by

*Laboratory preparation of methane

• From Alkyl halides (R-X) by

Reduction reaction

awurtz reaction

Decarboxylation

• Laboratory preparation of methane

What is cycloakanes?

Cycloakanes are cyclic hydrocarbon with only single carbon-carbon bonds

What is Alkanes (OLEFINS)

• Alkanes are unsaturated hydrocarbons containing at least one carbon-carbon double bond

between carbon atom..

1.4 .1 Classification of Alkenes

Alkenes are classified into two groups;

1. Symmetric alkanes

2. Asymmetric alkanes

What is symmetric alkanes.

These are Alkanes in which two same groups are being attached to the carbon-carbon double

bond .

What is asymmetric alkanes.

These are Alkanes in which two different groups are being attached to the carbon-carbon

double bond.

1.4.4 General methods of preparation of Alkenes

1. Dehydration of alcohol

2. Dehydrohalogenation of alkyl halides

3. Dehalogenation of vicinal dehalide

What is vicinal dehalide?

Vicinal dehalide is dihalide that the two halogen atoms are bond to the adjacent carbon.

1.4.5 physical properties of Alkenes

1. the first three Alkenes are gases, next few members are liquids and higher members are

solids

2. Ethylene is colourless gas with sweet odour while others are colourless

3. They are soluble in organic solvents like benzene but are insoluble in water 💦

4. Boiling points of Alkenes increases with the increase in molecular mass

5. Alkenes with branches have lower boiling points

1.4.6 Chemical properties of Alkenes

a) Hydrogenation (Additionof H2)

b) Halogenation (Additionof halogens)

c)Hydrohalogenation (Additionof hydrogen halides (H-X)

d) Hydration (Addition of H2O)

e) Combustion

f)polymerization

Combustion Reaction of Alkenes

(Complete combustion of ethene-excess supply of oxygen)

(Incomplete combustion of ethene-insufficient supply oxygen)

Polymerization is divided into two

1. Monomers

2. Polymers

• . During this reaction small molecules Called monomers

• Are assembled together into large molecules called polymers

1.4.7 Use of Alkenes

1. Ethylene is used to manufacture polythene

2. In combustion with oxygen,ethane is used oxyethylene flame which is used for cutting and

welding metal.

3. Ethene is also used as ripening agent for food

4. Alkenes are used prepare Alkanes,alcohols etc

1.5 ALKYNES (ACETYLENE)

• Alkynes are defined as unsaturated hydrocarbon compounds containing at least one carbon -

carbon triple bond between carbon atom.

Because of the triple bond, Alkynes are highly unsaturated hydrocarbons.

• Alkynes are also called acetylene.

• Formula of Alkynes {[CnH2n-2)

1.5.2 isomerism in Alkynes

a) chain isomerism

b) position isomerism

1.6.3 General methods of preparation of Alkynes. Alkynes are prepared

1. Action of water with calcium carbide

2. Dehydrohalogenation of vicinal and Germinal dihalides

3. Dehalogenation of tetrahalides

~dehydrohalogenation of vicinal and Germinal dihalides~this process undergoes two steps.

Step1 : Alcoholic KOH is used as catalysts to produce haloalkene

Step 2: sodamide is used as catalysts to produce Alkyne

• Define Germinal dihalide is dihalide that the two halogen atoms are bonded to the same

carbon atom.

Dehalogenation of tetrahalides? to prepare

In this process tetrahalides are heated with zinc dust to get Alkynes.

1.5.4 physical properties of Alkynes.

1. The first three Alkynes are gases,the next eight members are liquids and higher members are

solids

2. All Alkynes except ethane are odourless

3. Alkynes have slightly higher boiling points than corresponding Alkanes and Alkenes.

4. The melting and boiling points increases with increase in molecular mass or number of

number of carbon atoms.

5. They are less dense in water and they are insoluble in water.

1.5.5 Chemical properties of Alkynes

a) Hydrogenation (Addition of H2)

b) Halogenation (Addition of halogens)

c) Hydrohalogenation (Addition of Hydrogen Halides)

d) Combustion (Reaction with air)

1.5.6 uses of Alkyne

1. Acetylene is used in oxy- acetylene flame which is used for cutting and welding matals

2. acetylene is used in manufacture of westron

3. Alkynes are used in formation of aldehydes ,ketones,alkanes e tc

4. Alkynes are also used for manufacturing plastics and synthetic rubber

Define Aromatic hydrocarbons are which have pleasant aromatic.

For example cinnamon, vanilla, jasmine ......

Define Benzenoid

These are aromatic hydrocarbons that contain benzene ring structure.

Define Non Benzenoid?

These are aromatic hydrocarbons that do not contain benzene ring structure.

Benzene was discovered byMichael Faraday in {1825}

1.6.2 Classification of benzene

Benzene are classified into

1. Monosubstited benzene

2. Distributed benzene

3. Polysubstituted benzene

Define monosubstited benzene?

These are benzenes in which only one of the hydrogen atoms has been substituted.

Define distributed benzene?

These are benzenes in which two hydrogen atoms havbe been substituted.

Define polysubstituted benzene?

These are benzenes in which more than two two hydrogen atoms has been substituted.

1.64 Chemical properties of benzene

1. Combustion Reactions

2. Substitution reaction

Substitution reaction

Divided into two types

a) Halogenations

b) Nitration

1.6.5 Use of benzene

1. Benzene can be converted to styrene which is used in the manufacture of synthetic fibres like

nylon

2. Benzene is important sources of chemicals which are used as pesticides and detergents

3. Derivatives of benzene such as toluene is used in making explosive

4. Derivatives of benzene aniline are used as dyes and drugs

General formula Alkanes.

CnH2n+2

General formula Alkenes.

CnH2n

General formula of Alkynes

CnH2n-2

General formula cycloa