The main differences between alkanes, alkene and alkynes are their functional groups and degree of unsaturation.
Alkenes, alkanes and alkynes are all hydrocarbons. This means that they are organic molecules that contain only hydrogen and carbon in its molecular structure.
Alkanes have a general formula of CnH2n+2 , n being the number of carbon atoms in its molecular structure. Alkanes are known as saturated hydrocarbons. This is because it does not contain any pi bonds or double bonds in its structure. Alkanes contain only C-H and C-C bonds in its structure – only C-H bonds in the case of methane. They are also generally unreactive and will only undergo substitution reactions with halogens in the presence of ultra-violet light and combustion. Long-chain hydrocarbons can also undergo catalytic cracking.
Alkenes have a general formula of CnH2n, n being the number of carbon atoms in its molecular structure(n > 1). Alkanes are known unsaturated hydrocarbons as it contains a C=C bond in its structure. The C=C is its functional group. Compared to alkanes, alkenes can undergo a larger range of chemical reactions such as combustion and various addition reactions( , addition polymerisation, hydration etc).
Alkynes have a general formula of CnH2n-2, n being the number of carbon atoms in its molecular structure(n > 1). Alkynes have the highest degree of unsaturation compared to the alkanes and alkenes. This is due to the presence of carbon-carbon triple bonds in its structure. The carbon-carbon triple bonds also happen to be the alkyne functional group.