Basics of hydrocarbons for Edexcel GCSE Chemistry
This page covers the following topics:
2. Homologous series
3. Saturated compounds
Hydrocarbons are molecules containing only carbon and hydrogen, they are named according to the number of carbons present.
A homologous series is a group of hydrocarbons which all have the same general formula, an example of this is all alkanes have the general formula CnH2n+2 where 'n' is the number of carbons in the chain. Physical properties of molecules change up a homologous series.
When all carbon atoms are bonded to four different atoms, a molecule is considered saturated. Sometimes a carbon atom is only bonded to three different molecules and a double bond forms between two carbon atoms, this is an unsaturated molecule.
Why do unsaturated molecules decolourise bromine water?
The carbon-carbon double bond opens up and the carbons form a bond with the bromine atoms. When the bromine is removed from the water it loses its brown colour.
What does the name of the compound CH₄ start with?
What will the name of the compound C₄H₁₀ start with?
Is the boiling point of a long chained molecule higher or lower than the boiling point of a shorter molecule from the same homologous series?
The boiling point of a long chained molecule is higher.
Are long or short chain molecules from the same homogenous series more volatile?
Short chain molecules are more volatile.
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