Transcript Organic Chemistry

Hydrocarbons
Grade 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
Add bromine water (brown colour) to the
test tubes.
Br2
Differentiating alkanes from alkenes
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.