Back to: Organic Chemistry 100 Level
Welcome to class!
Hey there, champ! It’s always a joy to see you back in class. I love how focused and curious you are. Today’s lesson is all about Alkenes and Alkynes—two very important families of organic compounds that you come across more often than you think. Let’s learn about them together in a way that’s simple, clear and exciting. Ready? Let’s go!
Alkenes And Alkynes
What Are Alkenes and Alkynes?
Just like alkanes, alkenes and alkynes are hydrocarbons—compounds made up of only carbon and hydrogen. But here’s what makes them different:
Alkenes contain at least one double bond (C=C) between carbon atoms.
Alkynes contain at least one triple bond (C≡C) between carbon atoms.
Because of these multiple bonds, alkenes and alkynes are unsaturated hydrocarbons. This means they don’t have as many hydrogen atoms as they possibly could, since the double or triple bond takes up space.
Structure and Examples
Let’s look at a few examples:
Ethene (C₂H₄) → simplest alkene. Found in fruits like bananas when they’re ripening!
Propene (C₃H₆) → used to make plastics.
Ethyne (C₂H₂) → also called acetylene, used in welding torches.
Butyne (C₄H₆) → used in making synthetic rubber.
Just like alkanes, you can use the IUPAC naming system.
Alkenes use the suffix -ene, and alkynes use -yne.
Example:
CH₂=CH₂ → Ethene
CH≡CH → Ethyne
Physical and Chemical Properties
Alkenes and alkynes are usually colourless gases or liquids.
They are more reactive than alkanes because of the double or triple bonds.
They can undergo addition reactions, where the double or triple bond is broken, and atoms are added.
Addition Reaction Example
Let’s say you have ethene (C₂H₄) and you add bromine (Br₂) to it. The double bond breaks and the bromine atoms attach to the carbon atoms. This reaction helps to test for unsaturation—if a compound turns orange bromine water colourless, it’s an alkene or alkyne.
Everyday Example You’ll Relate To
Imagine you’re inflating a balloon. If you fill it just a little, it’s like an alkane—full but not stretched. But if you keep blowing and it stretches, that tension is like the double or triple bond in alkenes and alkynes—full of potential energy. That energy makes them reactive and useful in industry.
In Nigeria, alkenes are important in making plastics, synthetic fibres, and medicines, while alkynes like ethyne are used in metal welding—something you’ll see on roadsides or in workshops around your community.
Summary
- Alkenes have double bonds, alkynes have triple bonds.
- Both are unsaturated hydrocarbons.
- They are more reactive than alkanes.
- Alkenes and alkynes undergo addition reactions.
- They are widely used in industries, agriculture, and construction.
Evaluation
- What is the main difference between alkanes and alkenes?
- What is the simplest alkyne?
- What type of reaction do alkenes usually undergo?
- What does it mean for a compound to be unsaturated?
- Name the compound with the formula CH≡CH.
You did an amazing job today! You’re not just learning facts—you’re understanding how the world around you works. Whether it’s ripening fruits, welding metals, or making plastics, alkenes and alkynes are right there. Keep learning with Afrilearn—where every lesson is designed with love, care, and you in mind. You’re doing excellently well. See you in the next class!