Nature’s Chemistry #1: Homologous Series
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What is a homologous series?
A family of compounds with the same general formula and similar chemical properties that show a gradual change in physical properties
Hydrocarbon
Molecules which consist of hydrogen and carbon atoms only
Molecular formula
Formula which shows the number of atoms of the different elements which are present in one molecule of a substance (Eg H2O)
Full structural formula
A 2D drawing of a 3D molecule. It shows the atoms present and the position of a covalent bond.
Shortened structural formula
Shows the position of the atoms in the molecules without showing the bonds
Alkanes summary
• subset of Saturated hydrocarbons • end in -ane • only contain carbon to carbon single bonds • general formula CnH2n+2 • all insoluble in water • commonly used as fuels
Alkanes end in…
-ane
Isomer
Molecules which have the same molecular formula but different structural formula
Isomer pitfalls
• flipping it (if given an isomer with branch above, don’t just draw one with branch below) • drawing the branch nearer the right hand side of the molecule stead of the left • drawing a bend in the longest chain
Physical property
Something that can be observed or measured
As the number of carbon atoms increases…
the boiling point increases
As the size of the molecule increases,
The size of force of attraction also increases
What does it mean that alkanes have more intermolecular forces the bigger the molecule?
More energy is required to overcome the forces and convert the liquid into a gas
Chemical property
A property that becomes evident during a chemical reaction
Flammability
Ease of combustion
As the chain length increases…
Flammability decreases
Why are smaller alkanes more flammable?
They can mix with oxygen in the air
How do alkanes undergo combustion?
With oxygen in the air
What are the products of combustion?
Carbon dioxide, water
Testing for the products of combustion
CO2 - turns limewater milky WATER - turns cobalt chloride from blue to pink - melts at 0°C - boils at 100°C
Alkanes: Complete combustion
In a plentiful supply of oxygen, alkanes burn to produce only carbon dioxide and water
Alkanes: incomplete combustion
In a limited supply of oxygen, alkanes burn to produce carbon, carbon monoxide, and water
Saturated hydrocarbons
A hydrocarbon in which all carbon to carbon covalent bonds are single bonds
The effect of saturation on alkanes
Relatively unreactive, with the exception of combustion