HydrocarbonsGrade 10

Organic Chemistry

•Is the study of carbon-containing compounds except carbon dioxide, carbon monoxide and carbonates.

•What is made from organic materials?

–All living organisms.

–All petroleum products.

–Most drugs and medicines.

Hydrocarbons

•Hydrocarbons are organic substances that are made up of carbon and hydrogen only.

•Which of the following is/are hydrocarbon?

CH4 C2H5OH CO2 C6H6

Alkanes

•Alkanes are hydrocarbons obtained directly from crude oil.

•Alkanes are saturated hydrocarbons with a general formula CnH2n+2

•Saturated means :–the molecule has no C=C double bonds, –only carbon-carbon single bonds–the maximum number of atoms .– no atoms can add to it.

Finding the general formula of Alkanes

•The general formula is Cn H2n+2

•n is the number of carbon atoms.

•For n=1 C1H2(1)+2 CH4

•For n=2 C2H2(2)+2 C2H6

•For n=3 C3H2(3)+2 C3H8

•For n=4 C4H2(4)+2 C4H10

•For n=5 C5H2(5)+2 C5H12

Objective 3.1

Homologous series

•A homologous series is a family of compounds which has :

Same general formula. Similar chemical properties Successive members differ by CH2 Gradual change in their physical properties melting/boiling points, solubility etc.

Alkanes belong to the same homologous series.

Naming alkanes

•The name of the alkane starts with a part that indicates the number of carbon atom and ends with –ane

•When n=1 meth+ane = methane

•When n=2 eth+ane = ethane

•When n=3 prop+ane= propane

•When n=4 but+ane = butane

•When n=5 pent+ane= pentane

Structural formula

Is the structure that shows all the bonds in the molecule.

Drawing alkanes

•Only the bonding pairs between atoms are shown.

•A bond is represented by a small line.

Structures of alkanes

Ethane

Propane

Butane

Pentane

Alkenes

•These are obtained from the cracking of alkanes.

•They are unsaturated hydrocarbons

•They form a homologous series with a general formula CnH2n

•Unsaturated means :–the molecule has C=C double bonds.– we can add atoms to it.

Finding the general formula of Alkenes

•The general formula is Cn H2n

•n is the number of carbon atoms.

•For n=1 C1H2(1) CH2 NOT FOUND

•For n=2 C2H2(2) C2H4

•For n=3 C3H2(3) C3H6

•For n=4 C4H2(4) C4H8

•For n=5 C5H2(5) C5H10

Naming alkenes

•The name of the alkene starts with a part that indicates the number of carbon atom and ends with –ene

•When n=1 meth+ene = methene

•When n=2 eth+ene = ethene

•When n=3 prop+ene= propene

•When n=4 but+ene = butene

•When n=5 pent+ene= pentene

Structures of alkanes

Ethene

Propene

Butene

Pentene

Differentiating alkanes from alkenes

Br2

Add bromine water (brown colour) to the test tubes.

The colour will disappear in one tube only.Which tube is it?

Differentiating alkanes from alkenes

•Keep in mind that the brown colour is due to the presence of Br-Br.

.When Bromine is added to an alkene, the Br-Br bond will break and the double bond in the alkene will break too.

.An addition reaction will occur and the product formed will not contain Br-Br.

.This means the brown colour will disappear.

Differentiating alkanes from alkenes