Lesson plan of Introduction to Organic Chemistry: Kekulé's Postulates

Objectives (5-7 minutes)

1. Understand the historical context and the importance of Kekulé's postulates for Organic Chemistry, and how they contributed to the formation of organic compounds.
2. Identify Kekulé's postulates and understand how these postulates were fundamental to the structuring and prediction of chemical reactions.
3. Apply Kekulé's postulates to solve simple problems, such as building molecular structures and predicting possible reactions.

Secondary Objectives:

1. Develop self-directed research and study skills, encouraging students to seek information beyond the content presented in the classroom.
2. Stimulate students' critical thinking and argumentation skills by promoting discussions on the evolution of scientific concepts over time.
3. Foster students' interest in Chemistry, demonstrating the applicability of theoretical concepts to everyday practice.

Introduction (10-15 minutes)

1. Review of previous concepts (3-5 minutes): The teacher should begin the class by quickly reviewing previous concepts that are fundamental to understanding the topic of the class. This includes recapitulating what atoms, chemical bonds, and the difference between organic and inorganic compounds are. This review can be done through questions directed to the students to activate their prior knowledge.

2. Problem situations (3-5 minutes): Next, the teacher should present two problem situations that will arouse the students' interest and prepare them for the topic of the class. For example, you could ask: "How were scientists able to predict the structure of a molecule before they could see it?" and "Why is it important to understand the structure of a molecule in Organic Chemistry?"

3. Contextualization (2-3 minutes): The teacher should then contextualize the importance of the subject, explaining how Organic Chemistry is present in our daily lives, from the production of medicines to the manufacture of plastics. Examples of scientific discoveries that were made possible thanks to the understanding of the structure of molecules, such as the synthesis of aspirin, can be mentioned.

4. Introduction to the topic (2-4 minutes): To gain the students' attention, the teacher can introduce the topic by telling two interesting facts:

• Curiosity 1: "Did you know that Organic Chemistry, which studies carbon compounds, was initially called Vital Chemistry, because it was believed that only living organisms were capable of producing these complex substances?"

• Curiosity 2: "And that the dream of the German scientist Friedrich August Kekulé was to discover the structure of benzene, a very important organic compound in the chemical industry? He had an insight into the structure of benzene while he was sleeping and dreaming of a snake biting its own tail, which led him to propose the ring structure that we know today."

The teacher should then announce the topic of the class - "Introduction to Organic Chemistry: Kekulé's Postulates" - and begin explaining the content.

Development (20-25 minutes)

1. Activity "Building Molecules" (10-12 minutes): The teacher should divide the class into groups of up to 5 students. Each group will receive a set of cards with representations of carbon and hydrogen atoms, as well as bonds of different colors. The objective of the activity is for the students, using Kekulé's postulates, to build the molecular structures of simple organic compounds, such as methane (CH4), ethene (C2H4), and ethyne (C2H2).

• Step 1: Students should review Kekulé's postulates and chemical bonds, discussing in a group how they can be applied to build the molecules.
• Step 2: Students should take the cards and begin assembling the molecules, remembering to respect the valence of the atoms and the geometry of the bonds.
• Step 3: After assembly, each group should present their molecules to the class, explaining how they applied Kekulé's postulates.

2. Activity "Unveiling Benzene" (10-13 minutes): Still in groups, the students will receive a slightly more complex challenge: building the structure of benzene (C6H6).

• Step 1: The teacher should introduce the concept of resonance, explaining how it was fundamental to understanding the structure of benzene and how Kekulé's postulates relate to this phenomenon.
• Step 2: Students, using the cards and colored bonds, should try to build the structure of benzene. They should realize that the planar structure proposed by Kekulé is not sufficient to explain all the properties of benzene, and that it is necessary to consider the resonance between the forms with single and double bonds.
• Step 3: Each group should present their proposals for the structure of benzene and their considerations on resonance. The teacher should then correct and explain the correct structure, reinforcing the importance of critical thinking and experimentation in science.

3. Discussion and Reflection (5-7 minutes): After the conclusion of the activities, the teacher should promote a classroom discussion so that the students can share their experiences and difficulties. The teacher should ask questions that stimulate the students to reflect on what they have learned, such as "Why is the structure of benzene so important in Organic Chemistry?" and "How do Kekulé's postulates help us understand and predict chemical reactions?" The teacher should also clarify any doubts that may have arisen during the activities.

Feedback (10-12 minutes)

1. Group Discussion (3-5 minutes): The teacher should promote a group discussion with all students so that they can share the solutions or conclusions found by each group in the activities "Building Molecules" and "Unveiling Benzene". Each group will have up to 3 minutes to present their conclusions, highlighting how they applied Kekulé's postulates and resonance in building the molecules. The teacher should encourage everyone to participate, asking questions to ensure understanding of the concept and correct application of the postulates.

2. Connection with Theory (2-3 minutes): After the presentations, the teacher should make the connection between the practical activities and the theory of Kekulé's postulates. It should be emphasized how the structure of benzene, for example, was originally proposed by Kekulé and later confirmed experimentally. The teacher can also mention other contributions of Kekulé to Organic Chemistry, such as the idea that carbon can form chains and the concept of isomerism.

3. Individual Reflection (3-4 minutes): The teacher should propose that the students reflect individually on what they have learned in the class. To do this, the teacher should ask questions such as:

• "What was the most important concept you learned today?"
• "What questions have not yet been answered?"
• "How can you apply what you learned today to everyday situations?"

The students should write down their answers, which will be used to guide the review of the content in the next class.

4. Feedback (2-3 minutes): Finally, the teacher should ask the students for feedback on the dynamics of the class, the understanding of the content, and the clarity of the explanations. The teacher can ask questions such as:

• "Did the activity 'Building Molecules' help to understand Kekulé's postulates? How could we improve it?"
• "Was the activity 'Unveiling Benzene' challenging? What did you learn from it?"
• "Did you miss any content in today's class?"

Student feedback is extremely valuable for improving the planning of future classes and ensuring that the content is understood effectively.

Conclusion (5-7 minutes)

1. Summary of Content (2-3 minutes): The teacher should begin the Conclusion by summarizing the main points covered during the class. This includes the importance of Kekulé's postulates in Organic Chemistry, the structure of benzene, and how resonance and Kekulé's postulates were used to predict and understand chemical reactions. The teacher should emphasize how the class connected theory, practice, and the history of science, reinforcing the relevance of critical thinking and experimentation in science.

2. Connection between Theory, Practice, and Applications (1-2 minutes): The teacher should then explain how the class connected theory, practice, and applications. It should be emphasized how the activities "Building Molecules" and "Unveiling Benzene" allowed the students to apply Kekulé's postulates and resonance in the construction of molecular structures. The teacher can mention examples of practical applications of the concepts learned, such as the synthesis of medicines and the production of plastics.

3. Extra Materials (1-2 minutes): The teacher should suggest extra materials for students who wish to deepen their knowledge of the topic of the class. This may include books, articles, videos, and Chemistry websites that cover Kekulé's postulates and Organic Chemistry in more detail. The teacher may also suggest extra exercises for students who wish to practice building molecular structures and predicting chemical reactions.

4. Relevance of the Subject (1 minute): Finally, the teacher should emphasize the importance of the subject for the students' daily lives. It should be explained how understanding the structure of molecules and chemical reactions is fundamental to a variety of practical applications, from the production of medicines to the manufacture of materials for everyday use. The teacher can conclude the class by reinforcing the idea that Organic Chemistry, in addition to being a fascinating field of study, is a science that has a direct impact on everyone's lives.