Hydrocarbon Family: Alkanes, Alkenes, Alkynes

Why it matters

Imagine a carbon atom as a social butterfly with exactly four hands to hold. It never lets go, but it changes partners to fit the crowd.

Predict first

If a hydrocarbon molecule contains a carbon-carbon double bond, which family does it belong to?

The suffix '-ene' signals a double bond. Alkanes are single-bonded, alkynes are triple-bonded.

• Alkane
• Alkene — correct
• Alkyne
• Alcohol

What you do

Two carbons, four bonds each. Flip the bond between them single, double, then triple, and watch ethane become ethene then ethyne. Each extra C–C bond leaves room for two fewer hydrogens — and names a new family: alkane, alkene, alkyne.

Check yourself

Why is Methane (CH₄) classified as an alkane?

Alkanes are saturated hydrocarbons, meaning they contain only single covalent bonds. Methane has C-H single bonds only.

Which formula represents an alkyne?

Alkynes contain a carbon-carbon triple bond. C₂H₂ (Ethyne) requires a triple bond to satisfy carbon's valency of 4.

What is the general trend in hydrogen count as bond order increases from alkane to alkyne for the same number of carbons?

As carbon atoms use more valencies to bond with each other (double/triple), fewer valencies remain for hydrogen. C₂H₆ (alkane) > C₂H₄ (alkene) > C₂H₂ (alkyne).

• It contains only single bonds between carbon and hydrogen — correct
• It has a double bond between carbon atoms
• It is a gas at room temperature
• It contains four hydrogen atoms
• C₂H₆
• C₂H₄
• C₂H₂ — correct
• CH₄
• Hydrogen count increases
• Hydrogen count decreases — correct
• Hydrogen count stays the same