Hydrocarbons

This lesson covers:

  1. What 'organic chemistry' is
  2. What a 'hydrocarbon' is
  3. What an 'alkane' is
  4. The alkanes general formula: CnH2n+2
  5. What 'saturated' means for alkanes

Isomers

Isomers are molecules that have the same molecular formula, but different structural formulas, this means they are made of the same atoms, but the atoms are arranged differently.

Illustration showing two isomers with the molecular formula C5H12, highlighting different structural formulas.
Diagram showing the structural formulas of pentane and 2-methylbutane, both with the molecular formula C5H12.


For example, the two molecules above both have the formula C5H12 - meaning 5 carbon atoms and 12 hydrogen atoms. However the atoms are arranged differently, which is why they have different names.

Organic chemistry is about molecules that contain which element?

Carbon

Magnesium

Iron

Argon

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Diagram showing the molecular structure of propane with three carbon atoms and eight hydrogen atoms.

Is the molecule above a hydrocarbon?

Yes

No

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Diagram showing the molecular structure of propanol with carbon, hydrogen, and oxygen atoms.

Is the molecule above a hydrocarbon?

Yes

No

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Diagram showing the molecular structure of propene with carbon and hydrogen atoms.

Is the molecule above a hydrocarbon?

Yes

No

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Diagram showing the structure of alkanes with carbon and hydrogen atoms and single bonds.

Alkanes are a homologous series of molecules that contain:


  1. Only carbon and hydrogen atoms.
  2. Only single bonds (alkanes have no double bonds).

What is the definition of a homologous series? 

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Diagram showing the molecular structures of methane CH4 and ethane C2H6 labelled as A and B respectively.
Diagram showing the molecular structures of alkanes with labels C and D, representing propane and butane.

The names of alkanes always end in 'ane'.


Match the molecules A to D on the diagram above with their names:


Methane:

Butane:

Ethane:

Propane:


A
D
B
C

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Diagram showing the molecular structure of ethane with two carbon atoms and six hydrogen atoms.

Which alkane is shown above?

Methane

Ethane

Propane 

Butane

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Structural formula of butane showing carbon and hydrogen atoms.

Which alkane is shown above?

Propane 

Ethane

Methane

Butane

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Diagram illustrating the structure of an alkane chain with highlighted CH2 groups.

The alkane 'chain' can be very long. Longer alkanes simply have more CH2 groups (highlighted above) in the chain.

Each homologous series has its own general formula, which allows you work out how many atoms of each element a molecule will have. 


What is the general formula for alkanes? 


(Remember that 'n' represents the number of carbon atoms)

CnH2n

CnHn

CnH2n+2

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How many hydrogen atoms are there in an alkane with 5 carbon atoms?

12

hydrogen atoms

hydrogen atoms

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An alkane only has single covalent bonds. There are no double bonds or triple bonds.


What is another way to describe hydrocarbons with only single bonds?

Unsaturated

Lone molecules

Saturated

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What is the definition of a hydrocarbon? 

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