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Chapter 16
Chapter 16Alkanes and
AlkenesAlkanes and
Alkenes
ORGANIC CHEMISTRY
• Chemistry of CARBON compounds
• Organic compounds contain numerous carbon atoms
• Over 2 millions organic compounds need classifications
• Classified into families called “HOMOLOGOUS SERIES”
• 3 Homologous Series :
Alkanes
Alkenes
Alcohols
• PHYSICAL properties changes gradually down each series . As the number of carbon atoms in a molecule increases, boiling point increases, compound becomes less flammable and more viscous
HOMOLOGOUS SERIES
• A family of organic compounds with similar CHEMICAL properties• Chemical properties due to same FUNCTIONAL GROUP
AlkaneFunctional Group :
C – CCarbon-carbon Single Bond
H H H | | |H- C – C – C -H | | | H H H
FUNCTIONAL GROUPS
FUNCTIONAL GROUPS
Alkene
Functional Group :
C = CCarbon-carbon Double Bond
H H H
H- C - C = C – H
H
Alcohol
Functional Group :
-O – HHydroxy Group
H H | | H- C – C – O -H | | H H
FUNCTIONAL GROUP
NAMING OF ORGANIC COMPOUNDS
Naming is divided into 2 parts :
1st part tell the no. of carbon
1st part of name No. of carbon atoms
Meth-
Eth-
Prop-
But-
Pent-
Hex-
Hep-
Oct-
1
2
3
4
5
6
7
8
NAMING OF ORGANIC COMPOUNDS
2nd part shows the homologous series of compound
Name ending Homologous Series
-ane
-ene
-ol
Alkane
Alkene
Alcohol
Deduce the structure of
PROPANE
3 carbon atoms alkane
H H H | | |H- C – C – C -H | | | H H H
Alcohol = -ol
H H H H H | | | | |H- C – C – C – C – C – O -H | | | | H H H H H
5 carbon atoms = PENT
What is the chemical name of
PENTANOLWhat is the molecular formula ?
PHYSICAL PROPERTIES
1) Boiling Points
2) Solubility
BOILING POINTS
ALKANESNo. of carbon
Chemical Name
Molecular Formula
Rel. Molecular
Mass
Structural Formula Boiling Point
1 Methane CH4 16 H
|
H- C –H
|
H
-162
2 Ethane C2H6 30 H H
| |
H- C – C –H
| |
H H
-89
3 Propane C3H8 44 H H H
| | |
H- C – C – C –H
| | |
H H H
-42
4 Butane C4H10 58 H H H H
| | | |
H- C – C – C – C –H
| | | |
H H H H
-0.5
BOILING CURVE OF ALKANESB
oilin
g P
oin
t o C
200
150
100
50
0
-50
-100
-150
-200
No. of Carbon2 4 6 8 10
Methane
Ethane
Propane
ButanePentane
Hexane
The boiling point increases down a homologous series
BOILING POINTS
Alkanes are covalent compounds. They have low boiling point
Alkanes are gases or liquids at room temperature.
Why does boiling point increases down a homologous series?
BOILING POINTS
As carbon number increases, molecular size also increases.
The larger the size of molecules, the greater is the van der Waals forces
between them
SOLUBILITY
THREE
SOLUBILITY OF ALKANES
From these products, what can you say about the solubility of alkanes?
Refer to Handout “Chief Uses of Oil Products”
They are not soluble because they are oil-based
SOLUBILITY OF ALKANES
All alkanes are NOT soluble
alkanesalkanes
a group of organic compounds with the general formula, CnH2n+2, where n is the number of carbon atoms in one molecule
names of alkanes end in –ane
are molecular compounds
have low boiling points; tend to be liquids and gases at room conditions
are insoluble in water
a group of organic compounds with the general formula, CnH2n+2, where n is the number of carbon atoms in one molecule
names of alkanes end in –ane
are molecular compounds
have low boiling points; tend to be liquids and gases at room conditions
are insoluble in water
alkanesalkanes
a ball-and-stick model of methane,
CH4
alkanesalkanes
alkanes burn in air to form CO2 and H2O
example: combustion of propane, C3H8
alkanes burn in air to form CO2 and H2O
example: combustion of propane, C3H8
combustioncombustion
C3H8 + 5O2 3CO2 + 4H2O
incomplete combustion results in the formation of carbon monoxide, CO and soot, C
incomplete combustion results in the formation of carbon monoxide, CO and soot, C
alkanesalkanes
main use of alkanes is in combustion to produce energy:
main use of alkanes is in combustion to produce energy:
o bottled gas for cookingo fuels for buses and carso fuels for aircrafts
o bottled gas for cookingo fuels for buses and carso fuels for aircrafts
uses of alkanesuses of alkanes
alkanesalkanes
alkanes react with chlorine in the presence of light
example: substitution reaction of methane with chlorine
alkanes react with chlorine in the presence of light
example: substitution reaction of methane with chlorine
substitution with chlorinesubstitution with chlorine
CH4 + Cl2 CH3Cl + HCl
o a hydrogen atom in methane is replaced by a chlorine atom
o This is called a substitution reaction
o more hydrogen atoms in methane can be replaced by chlorine atoms to produce organic halogen compounds (CH2Cl2, CHCl3 and CCl4)
o a hydrogen atom in methane is replaced by a chlorine atom
o This is called a substitution reaction
o more hydrogen atoms in methane can be replaced by chlorine atoms to produce organic halogen compounds (CH2Cl2, CHCl3 and CCl4)
Story of a Star
Starry
Candies!!!
Starry
Substitution
Substitution
Starry
Time for Chemistry!
Starry
Carbon atom
Hydrogen atom
Chlorine atom
Covalent bonds
Time for Chemistry!
Starry C
H
H
H
H
Cl Cl
Time for Chemistry!
C
H
H
Cl
HStarry
H Cl
Substitution Reaction
• A reaction in which one or more atoms of an organic compound are replaced with one or more other atoms
C
H
H
H
H C
H
H
Cl
H
• Methane + Chlorine Monochloromethane + Hydrogen Chloride
+ Cl-Cl + HCl
CH4 + Cl2 CH3Cl + HCl
monochloromethane
Substitution Reaction
• Write out the substitution equations if monochloromethane is further substituted with more chlorine molecules. What will the final product be?
CH4(g) + Cl2(g) CH3Cl (g) + HCl (g)
monochloromethane
Substitution Reaction
When more chlorine is added,
+ +C
H
H
Cl
H C
H
Cl
Cl
HCl-Cl HCl
CH3Cl (g) + Cl2(g) CH2Cl2(g) + HCl (g)
dichloromethanemonochloromethane
Substitution Reaction
When more chlorine is added,
C
H
Cl
Cl
H C
Cl
Cl
Cl
H+ Cl-Cl + HCl
CH2Cl2(g) + Cl2(g) CHCl3(l) + HCl(g)
trichloromethane
For your information :
Trichloromethane is commonly called chloroform and is very useful as an anaesthetic
dichloromethane
Substitution Reaction
When more chlorine is added,
C
Cl
Cl
Cl
H C
Cl
Cl
Cl
Cl+ Cl-Cl + HCl
CHCl3 + Cl2 CCl4 + HCl
tetrachloromethane
For your information :
Tetrachloromethane is a valuable solvent, used in dry cleaning because it is very volatile and good at dissolving grease and dirt.
trichloromethane
Summary
• Alkanes
- CombustionAlkanes + Oxygen
Carbon dioxide + water
- Substitution- with Chlorine to form
variety of substituted products
End of alkanes
Coming soon : test on fuels and alkanes
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