Unit 3, Topic 2:

Alkenes and Alkynes

Lesson Instructions

Review the learning goals and success criteria for Topic 2: Alkenes and Alkynes.
- Review the minds on, action, and consolidation sections of the lesson, completing any tasks as outlined.
- Complete the fill-in-the-blanks handouts that have been provided to you. They have been linked below.
- Practice and apply what you've learned by completing the practice tasks outlined at the end of the lesson.

Learning Goals

I am learning to ...

- Identify, name, and draw alkenes and alkynes.

Minds-On

Saturated and unsaturated hydrocarbons provide the chemistry behind the saturated and unsaturated fats in our diet. The presence and quantity of double bonds in the parent chains of these compounds help distinguish the monounsaturated, polyunsaturated, and trans fats from saturated fats.

Action

Alkenes

- Hydrocarbons that contain one or more double bonds. [ending: -ene].

Alkynes

- Hydrocarbons that contain one or more triple bonds. [ending: -yne].

All three of these examples are based on the five (5) carbon parent chain, pentane. However, notice how the ending of each name changes in the presence of a double or triple bond.

Why do double and triple bonds form?

Covalent bonding occurs when electrons are shared between atoms. Double and triple covalent bonds occur when four or six electrons are shared between two atoms, and they are indicated in Lewis structures by drawing two or three lines connecting one atom to another.

When naming these molecules, there are a few extra rules to follow. These are in addition to the naming rules from Topic 1: Alkanes.

Additional Rules for Naming Alkenes and Alkynes

The main chain (parent chain) must include the double or triple bonds at the lowest position number (indicate the position number).
Alkenes end with -ene, alkynes end with yne.
When numbering the main chain, double and triple bonds have priority over the alkyl branch.
This means if we have to choose between keeping a double/triple bond at a low position number, or an alkyl branch at a low position number, we will choose the double/triple bond.