Objectives (5 - 10 minutes)

1. Understand the basic concepts of molecular geometry: Students should be able to understand and describe the fundamental concepts of molecular geometry, including the definition of molecular geometry, the importance of understanding the shape of molecules, and the relationship between the structure and property of molecules.

2. Apply the Valence Shell Electron Pair Repulsion (VSEPR) model: The objective is for students to apply VSEPR to deduce the molecular geometry of a given molecule. They should be able to predict the molecular geometry of a molecule, knowing the number of valence electron pairs in the molecule.

3. Solve practical problems of molecular geometry: Students should be able to solve practical problems, such as determining the molecular geometry of a specific molecule, using VSEPR.

Secondary Objectives:

• Stimulate critical thinking and problem-solving: In addition to understanding and applying the concepts, students should be encouraged to think critically and work to solve practical problems. This will help develop their critical thinking and problem-solving skills.

• Promote collaboration and communication: During problem-solving, students should be encouraged to collaborate and communicate with each other. This will not only help improve their teamwork skills but also enhance their communication skills.

Introduction (10 - 15 minutes)

1. Content Review: The teacher should start the lesson by briefly reviewing the basic concepts that will be necessary for understanding the lesson topic. This may include the structure of the atom, the formation of chemical bonds, and the distribution of electrons in energy levels and sublevels.

2. Problem Situations: The teacher can present two problem situations to arouse students' interest and demonstrate the relevance of the topic. For example:

   • "Why is water a polar compound and carbon dioxide is nonpolar, even though both are formed by covalent bonds?"
   • "How is it possible that ammonia, which has four valence electron pairs, has a pyramidal molecular geometry, while methane, which also has four valence electron pairs, has a tetrahedral molecular geometry?"

3. Contextualization: The teacher should then contextualize the importance of studying molecular geometry, explaining that the shape of a molecule influences its physical and chemical properties, including polarity, solubility, boiling point, among others. Practical examples can be cited, such as the importance of molecular geometry in understanding the structure and reactivity of organic compounds, in the synthesis of new materials and medicines, and even in understanding natural phenomena, such as the greenhouse effect.

4. Introduction to the Topic: The teacher should introduce the topic of molecular geometry, explaining that the geometry of a molecule is determined by the repulsion between valence electron pairs, and that there are different ways to arrange these electron pairs around a central atom.

5. Curiosities: To arouse students' curiosity, the teacher can share some curiosities, such as:

   • "Did you know that the shape of the DNA molecule, a double helix, was discovered by James Watson and Francis Crick in 1953, through the study of its molecular geometry?"
   • "And that the shape of the fullerene molecule, a carbon allotrope shaped like a soccer ball, was predicted before it was even synthesized in the laboratory, through the study of its molecular geometry?"

This Introduction should help spark students' interest in the topic, showing its relevance and practical application, and prepare them for the Development of the lesson content.

Development (20 - 25 minutes)

1. Theory of Molecular Geometry (10 - 12 minutes): The teacher should start the theoretical part of the lesson by explaining the concept of molecular geometry. They should emphasize that the geometry of a molecule is the three-dimensional arrangement of the atoms that compose it, excluding the contribution of free electrons. The teacher can use molecular models or drawings to illustrate different geometries, such as linear, trigonal planar, tetrahedral, pyramidal, angular, and trigonal bipyramidal.

   • Definition of molecular geometry: The teacher should explain that molecular geometry is the three-dimensional arrangement of the atoms that form a molecule.
   • Importance of understanding the shape of molecules: The teacher should emphasize that the shape of a molecule determines many of its physical and chemical properties, including polarity, solubility, boiling point, among others. Therefore, understanding molecular geometry is essential to predict and explain the behavior of molecules.
   • Examples of molecular geometry: The teacher should present examples of molecules with different geometries, explaining how the geometry is determined by the number and type of bonds and valence electron pairs.

2. Valence Shell Electron Pair Repulsion (VSEPR) Model (5 - 7 minutes): The teacher should then introduce the Valence Shell Electron Pair Repulsion (VSEPR) model. They should explain that this model describes how valence electron pairs around a central atom move away from each other to minimize repulsion and thus determine the molecule's geometry.

   • Principle of VSEPR: The teacher should explain that, according to VSEPR, valence electron pairs around a central atom, whether a bonding electron pair or a non-bonding electron pair, will repel each other. They should emphasize that this repulsion is greater between non-bonding electron pairs than between a bonding electron pair and a non-bonding electron pair.
   • Rules of VSEPR: The teacher should present the rules of VSEPR, which are:
     1. Valence electron pairs around a central atom move as far apart as possible to minimize repulsion.
     2. Repulsion between non-bonding electron pairs is greater than the repulsion between a bonding electron pair and a non-bonding electron pair.
     3. Repulsion between bonding electron pairs is minimized.
   • How to use VSEPR to determine molecular geometry: The teacher should explain that, to determine the molecular geometry of a molecule using VSEPR, we must:
     1. Count the total number of valence electron pairs around the central atom.
     2. Deduce the molecular geometry following the rules of VSEPR.

3. Problem Solving with VSEPR (5 - 6 minutes): The teacher should then present some examples of problems involving VSEPR and molecular geometry, and guide students in solving these problems. The teacher should explain each step of the resolution, showing how to apply VSEPR to determine the molecular geometry.

   • Example 1: The teacher can start with a simple example, such as determining the molecular geometry of a molecule with only one central atom and two valence electron pairs. The teacher should explain that, according to VSEPR, electron pairs move as far apart as possible, leading to a linear geometry.
   • Example 2: Next, the teacher can present a more complex example, such as determining the molecular geometry of a molecule with a central atom and four valence electron pairs. The teacher should explain that, according to VSEPR, the geometry will be tetrahedral if all electron pairs are bonding, or pyramidal if there is a non-bonding electron pair. The teacher should guide students in counting the electron pairs and deducing the molecular geometry.

The Development of the lesson should help students understand the concepts of molecular geometry and VSEPR, and apply these concepts to solve practical problems. The teacher should be attentive to clarify any doubts that may arise and ensure that all students are keeping up with the pace of the lesson.

Return (10 - 15 minutes)

1. Concept Review (5 - 7 minutes): The teacher should start the Return stage by reviewing the main concepts covered in the lesson. The teacher can ask students questions to verify their understanding of the concepts.

   • Question 1: "What is molecular geometry and why is it important for chemistry?"
   • Question 2: "How does the Valence Shell Electron Pair Repulsion (VSEPR) model help us predict the geometry of a molecule?"
   • Question 3: "How can we use VSEPR to determine the molecular geometry of a molecule?"

2. Connection between Theory and Practice (3 - 5 minutes): The teacher should then connect the presented theory with practice. This can be done through practical examples that demonstrate the application of theoretical concepts.

   • Example 1: The teacher can recall the example of water and carbon dioxide presented in the Introduction of the lesson. They can explain that the molecular geometry of water, which is angular, makes it polar, while the molecular geometry of carbon dioxide, which is linear, makes it nonpolar. This influences their properties, such as solubility and the ability to form hydrogen bonds.
   • Example 2: The teacher can present a new example, such as the molecular geometry of methane, which is tetrahedral due to the repulsion between the four valence electron pairs, all of them bonding. This contributes to the stability of methane and its low reactivity.

3. Reflection on Learning (2 - 3 minutes): The teacher should then ask students to reflect on what they learned in the lesson. They can do this by answering questions like:

   1. "What was the most important concept you learned today?"
   2. "What questions do you still have about molecular geometry and VSEPR?"

4. Homework Assignment (1 minute): Finally, the teacher should assign homework that reinforces the concepts learned. The assignment may include solving additional problems, researching the geometry of specific molecules, and preparing for the next lesson. The teacher should clearly explain what is expected of the students and when the assignment should be submitted.

The Return stage is a crucial part of the lesson plan, as it allows the teacher to check if students understood the concepts presented and are able to apply them. In addition, reflecting on learning and homework assignments help consolidate the acquired knowledge and prepare students for future lessons.

Conclusion (5 - 7 minutes)

1. Summary of Contents (2 - 3 minutes): The teacher should summarize the main points covered during the lesson. This includes the definition of molecular geometry, the importance of understanding the shape of molecules, the Valence Shell Electron Pair Repulsion (VSEPR) model, and how to use it to determine the molecular geometry of a molecule. The teacher can recall the practical examples used during the lesson to illustrate these concepts.

2. Connection between Theory, Practice, and Applications (1 - 2 minutes): The teacher should highlight how the lesson connected theory, practice, and applications. The teacher can recall the practical examples used during the lesson to demonstrate the application of theoretical concepts. They should emphasize that understanding molecular geometry and VSEPR is essential to predict and explain the behavior of molecules, and that this has applications in various fields, such as chemistry, biology, medicine, materials engineering, among others.

3. Extra Materials (1 minute): The teacher should suggest some extra materials for students who wish to deepen their knowledge on the topic. This may include chemistry books, educational websites, and videos on molecular geometry and VSEPR. The teacher can also suggest some additional exercises for students to practice determining molecular geometry.

4. Relevance of the Topic (1 - 2 minutes): Finally, the teacher should reinforce the importance of the topic for students' daily lives. They should explain that the geometry of a molecule determines many of its properties, and that this has implications in various everyday situations. The teacher can cite examples, such as the influence of molecular geometry on compound solubility, the effectiveness of medications, the composition of the atmosphere, and the functioning of electronic devices.

The Conclusion is an essential stage of the lesson plan, as it allows the teacher to recap the main points of the lesson, reinforce the connection between theory, practice, and applications, and highlight the relevance of the topic for students. Additionally, by suggesting extra materials and emphasizing the importance of the topic, the teacher stimulates independent learning and students' curiosity.