Welcome to a new family. The alkanes Methane (CH 4 ) Draw a dot and cross diagram to represent the...
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Transcript of Welcome to a new family. The alkanes Methane (CH 4 ) Draw a dot and cross diagram to represent the...
Welcome to a new family
The alkanes
Methane (CH4)
Draw a dot and cross diagram to represent the bonding shown here.
What shape are the bonds around the carbon atom? Why?
Ethane (C2H6)
Draw a dot and cross diagram for ethane.
What shape will the bonds take around each carbon atom now?
Propane (C3H8)
Butane (C4H10)
The Alkanes: molecular formula or displayed formula?
Methane CH4
Ethane C2H6
Propane C3H8
Butane C4H10
Pentane C5H12
Hexane C6H14
Octane C8H18
The alkanes CnH2n + 2
Methane CH4
Ethane C2H6
Propane C3H8
Butane C4H10
Pentane C5H12
Hexane C6H14
Octane C8H18
General formula
Homologous series:
Same general formula, similar chemical properties but a graduation in physical properties
The alkanes CnH2n + 2
Methane CH4
Ethane C2H6
Propane C3H8
Butane C4H10
Pentane C5H12
Hexane C6H14
Octane C8H18
General formula
Generally unreactive, but burn exothermically.
Longer chains burn less easily.
COPY!
You have to be able to explain
this
Structural formulae
Alkanes are saturated compounds
No double bonds
Isomers
Same molecular formula, but different structures (arrangement of atoms)
Name? Name of this?
Why does this have lower boiling point?
Isomers
Draw out pentane.
How many other isomers can you draw?
Stretch yourself – can you name them?
Reactions of the Alkanes
Combustion
Chlorination
Combustion
Combustion
Hydrocarbons combust well. What does this mean?
What do you predict the products are of this reaction?
They burn producing carbon dioxide and water
Write a word equation for this reaction, then try a chemical equation
For example, with methane:CH4 + 2O2 CO2 + 2H2O
Incomplete combustion
How do you think this reaction is different?
What do you think the products are this time?
Why is this reaction so dangerous?
Who should be careful?
Hurricane Ike link
Incomplete combustion
When there is insufficient oxygen, carbon monoxide is also formed
It reduces the blood’s oxygen carrying capability
Chlorination of Methane
Alkanes react with chlorine in sunlight:
CH4 + Cl2 CH3Cl + HCl
How would you describe this reaction?A chlorine atom takes the place of a hydrogen atom
= substitution reaction.
What would happen if lots more chlorine was present?
