6.2.1 Types of hydrocarbon & 6.2.2 Alkanes

What are hydrocarbons?

• Hydrocarbons are organic compounds containing carbon and hydrogen atoms only.

• They do not contain any other elements.

Where are hydrocarbons commonly found?

Hydrocarbons are found in crude oil and are important fuels and chemical feedstocks.

What are the two types of hydrocarbons?

Aliphatic and Aromatic

What is an Aliphatic hydrocarbon?

• A hydrocarbon where carbon atoms are joined in straight chains, branched chains, or non-aromatic rings.

• Key feature: Electrons are fixed in standard single or double bonds.

What are Aromatic hydrocarbons?

• A hydrocarbon containing one or more benzene rings.

• Key feature: Contains a stable ring with a delocalised pi -electron cloud shared across the carbons.

What are Alkanes?

• Alkanes are hydrocarbons containing carbon and hydrogen only.

• They are saturated hydrocarbons.

• They contain only single covalent bonds between their carbon atoms.

What is the general formula of the alkanes?

CnH2n+2

What does Saturated mean?

• Contains only single carbon-carbon bonds.

• Has the maximum possible number of hydrogen atoms for its carbon skeleton.

• Does not contain carbon-carbon double or triple bonds.

What are two saturated families of saturated hydrocarbons?

• Cycloalkanes are hydrocarbons containing a carbon ring.

• They contain only single carbon-carbon bonds.

• They are saturated because they do not contain carbon-carbon double or triple bonds.

What is the general formula of the cycloalkanes?

CnH2n

What are the intermolecular forces that hold together alkanes?

London dispersion forces

What are London forces?

• London forces are attractions between temporary instantaneous dipoles and induced dipoles.

• These forces act between separate alkane molecules, NOT between the atoms within an individual molecule.

• The covalent bonds within each alkane molecule are much stronger than the intermolecular forces.

What happens when you increase the carbon chain length of an alkane?

1. The alkane molecules become larger.

2. They contain more electrons.

3. Their electron clouds become more polarisable.

4. London forces become stronger.

5. More energy is required to overcome these intermolecular forces.

6. Therefore, boiling temperatures increase.