There is a lot going on when halogenalkanes and hydroxide ions react

Today, I used my own variation of the generate-sort-connect-elaborate routine from the Visible Thinking Project to help students uncover for themselves the central ideas concerning these two reactions.

The context for this activity is nucleophilic substitution and elimination reactions. Prior to the routine students had learned about nucleophilic substitution reactions and SN1 and SN2 mechanisms. An elimination reaction was seen for the first time during the routine.

Steps

GENERATE Students look at the SN2 and E2 reaction mechanisms below and generate a list of words, ideas or aspects associates with the two mechanisms. To make good connections I found that the students needed a minimum of five ideas for each mechanism.

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Conditions: heat strongly under reflux. Concentrated NaOH. Ethanol is used as a solvent.

SORT Students sort their ideas into two lists

CONNECT Students connect their ideas by drawing lines (or some other type of connection) between ideas that share a connection.

ELABORATE Students consider the connections and sort them into those that are more central or more important when comparing these two reactions and those that are peripheral or less important.  Students share with the class their central ideas and elaborate on them. To help them elaborate ask “What makes you say that?”.

What did the students think? Their central ideas were

The conditions of the reaction determines the products produced

Substitution and elimination reactions proceed by different mechanisms (movement of electrons, leaving atoms)

the type of halogenalkane (primary, secondary, tertiary) determines whether a substitution and / or elimination reaction occurs

During the activity the students for the most part worked independently to generate and sort their ideas. During the GENERATE step I found that a minimum of five ideas for each mechanism was needed to make good connection. It was the CONNECT stage that generated the most discussion and collaboration between students.

By making their thinking visible in this way I gained rich information about what students knew about reaction mechanisms and whether they could identify the central / most important ideas. I was so pleased they GOT IT!

IB Links NOTES
Group 4 Aims
Prior knowledge nucleophilic substitution reactions and the SN1 and SN2 mechanism
Chemistry syllabus & cross curricular links 10.2, 20.1
Learner Profile thinkers, knowledgeable, reflective
IB Approaches to Teaching inquiry based, conceptually focused
IB Approaches to Learning thinking skills
Assessment Formative

 

 

Reference:

Ritchhart, R., Church, M., & Morrison. (2011). Making Thinking Visible. San Francisco: Josseyboss.

 

 

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