Hydrocarbons & Alkanes (CIE A Level Chemistry)

• Organic chemistry is the chemistry of carbon compounds
• Carbon forms a vast number of compounds because it can form strong covalent bonds with itself
• This enables it to form long chains of carbon atoms, branched chains or cycles, and hence an almost infinite variety of carbon compounds are known
• Carbon always forms four covalent bonds which can be single, double or triple bonds

Examples of carbon structures

There is an almost infinite variety of chains, branches and rings able to form

• A functional group is a specific atom or group of atoms which confer certain physical and chemical properties onto the molecule
• Organic molecules are classified by the dominant functional group on the molecule
• Organic compounds with the same functional group, but with each successive member different by CH₂ are called a homologous series
  • Every time a carbon atom is added to the chain, two hydrogen atoms are also added, which is why the successive members differ by CH₂

• Hydrocarbons are compounds that are made up of carbon and hydrogen atoms ONLY

Examples of hydrocarbons

Ethanol is NOT a hydrocarbon as the molecule also contains an oxygen atom and is not solely made up of carbon and hydrogen

• A functional group is an atom or a group of atoms in an organic molecule, which determines the physical and chemical properties of the molecule
• Alkanes are the simplest hydrocarbons with no functional group
• They are made up of carbon and hydrogen atoms bonded to each other with single covalent bonds

Different types of alkanes

Alkanes are compounds made up of carbon and hydrogen atoms only and contain no functional group

Homologous Series of Alkanes Table

Name of alkane	Number of carbons	Chemical formula	Boiling point in °C	State at room temperature	Melting point in °C
Methane	1	CH4	-162	gas	-183
Ethane	2	C2H6	-89	gas	-172
Propane	3	C3H8	-42	gas	-188
Butane	4	C4H10	0	gas	-138
Pentane	5	C5H12	36	liquid	-130