Alkenes
High School
Definition
Hydrocarbons that contain at least one carbon–carbon double bond, with the general formula CₙH₂ₙ. The double bond makes alkenes more reactive than alkanes and allows addition reactions, including the formation of polymers.
Worked examples
\(\)C\(_2\)H\(_4\) (ethene): \(\)H\(_2\)C\({=}\)CH\(_2\)
The simplest alkene with one double bond; two carbons means \(2 \times 2 = 4\) hydrogens.
\(\)C\(_3\)H\(_6\) (propene): \(\)H\(_2\)C\({=}\)CH\({-}\)CH\(_3\)
Three carbons with one double bond; the formula \(\)C\(_n\)H\(_{2n}\) holds: \(n=3\), \(2n=6\).
Common mistakes
- Calling \(\)C\(_3\)H\(_8\) an alkene because it has three carbons → \(\)C\(_3\)H\(_8\) is propane (an alkane); propene is \(\)C\(_3\)H\(_6\) Alkenes follow \(\)C\(_n\)H\(_{2n}\), not \(\)C\(_n\)H\(_{2n+2}\); the double bond removes two hydrogens.
- Assuming alkenes and alkanes react the same way → Alkenes undergo addition reactions; alkanes mainly do substitution The double bond in alkenes makes them more reactive and allows atoms to add across the bond.
- Writing the double bond anywhere without checking carbon valence → Each carbon forms exactly four bonds total A double bond uses two of carbon's four bonds, leaving two for other atoms or groups.
Where you'll use it next
You'll use alkenes when studying addition reactions like hydrogenation and halogenation, polymerization to make plastics, and organic reaction mechanisms in advanced chemistry.
Found in 1 StudyPug lesson
Mastering Alkenes and Unsaturated Hydrocarbons
11th Grade11thChemistry 11
Dive into the world of alkenes and unsaturated hydrocarbons. Understand their unique structure, reactivity, and industrial applications. Enhance your organic chemistry knowledge with our comprehensive lessons.
See also
Reviewed by Pat Cheng, M.Ed. — StudyPug Curriculum Lead · Last updated June 6, 2026