Learning Objectives (5 - 7 minutes)

1. Understand the concept of molecular formula: Students should be able to define molecular formula, understand its significance, and how it is used to represent the chemical makeup of a substance.

2. Learn to calculate molecular formula: Students should be able to apply the concepts of empirical formula and molar mass to determine the molecular formula of a substance. This involves the ability to manipulate chemical formulas and use the periodic table to obtain molar masses.

3. Develop problem-solving skills: Through practice in molecular formula calculations, students should develop problem-solving skills, including critical thinking, analysis, and application of concepts.

Sub-objectives:

• Encourage active participation: The teacher should encourage active student participation by asking questions, facilitating discussions, and providing constructive feedback.

• Promote independent learning: The teacher should guide students to explore and practice the content beyond the classroom setting through assigned readings, homework assignments, and online activities.

Introduction (10 - 12 minutes)

1. Review of prior concepts: The teacher should begin the lesson by reviewing the concepts of percent composition and empirical formula, which are fundamental to understanding the topic of the lesson. This review can be done through direct questioning of students or through a brief slide presentation. (2 - 3 minutes)

2. Problem situations: The teacher can present students with two problem situations that will drive the development of the lesson. The first could be to determine the molecular formula of a substance given its empirical formula and molar mass. The second could involve manipulating a molecular formula to find the empirical formula. These problem situations should be challenging enough to stimulate students' critical thinking but not so complex as to discourage them. (3 - 4 minutes)

3. Contextualization: The teacher should then contextualize the importance of the topic by explaining how determining molecular formula is crucial in the chemical industry, medicine, pharmacy, and more. The teacher can cite real-world examples, such as determining the molecular formula of a drug to ensure its effectiveness or determining the molecular formula of a polymer to control its physical properties. (2 - 3 minutes)

4. Attention grabber: To pique students' interest, the teacher can share some fun facts related to the topic. For instance, they could mention that the longest known molecular formula is that of titin, a human protein with 189,819 atoms that would take about 1.5 hours to pronounce. Another fun fact is that the molecular formula for sugar (C12H22O11) is the same for sucrose, lactose, and maltose, even though they are substances with different chemical and physical properties. (2 - 3 minutes)

Development (20 - 25 minutes)

1. Modeling Activity - "Building Formulas" (10 - 12 minutes)

   • Preparation: The teacher should prepare a set of cards in advance, each with an atom and a number next to it. The atoms can be represented by their initials (e.g., O for oxygen, C for carbon, H for hydrogen, etc.), and the numbers represent the quantity of that type of atom in the molecular formula (e.g., 2 for carbon dioxide, 3 for diantimony trioxide, etc.). The teacher should also prepare a periodic table to assist students in the activity.

   • Implementation: Students, divided into groups of up to 5, should be given a set of random cards and the task of using the cards and the periodic table to build the molecular formula of a chemical substance. The teacher should guide students to start by building the empirical formula and then the molecular formula, checking the correctness of the procedure.

   • Discussion: After completing the activity, the groups should present their molecular formulas to the class and discuss the process of building, highlighting any difficulties encountered and how they were resolved. The teacher should use the discussion to reinforce the concepts of empirical formula and molecular formula and the importance of the periodic table and molar masses.

2. Practice Activity - "Determining Molecular Formulas" (10 - 12 minutes)

   • Preparation: The teacher should prepare a set of problems that involve determining the molecular formula from the empirical formula and the molar mass in advance.

   • Implementation: Students, still divided into groups, should be given the problems and the task of solving them. To do this, they should first calculate the molar mass of the empirical formula and then multiply all the subscripts in the empirical formula by the same number (so that the sum of the subscripts equals 1). The result will be the molecular formula.

   • Discussion: After completing the problem-solving, the groups should present their solutions to the class. The teacher should discuss the solutions, clarify any doubts, and provide constructive feedback. The teacher should also emphasize the importance of checking the correctness of the obtained molecular formulas, for example, by calculating the molar mass.

3. Game Activity - "Molecular Formula Challenge" (5 - 7 minutes)

   • Preparation: The teacher should prepare a set of cards with molecular formulas of various chemical substances in advance.

   • Implementation: Students, still divided into groups, should be given the cards and the task of identifying the corresponding substances. To do this, they should manipulate the molecular formulas, for example, by removing or adding atoms, and checking if the empirical formula and molar mass match those of the given substance.

   • Discussion: After completing the activity, the groups should present their answers to the class. The teacher should discuss the answers, clarify any doubts, and provide constructive feedback. The teacher should also emphasize the importance of checking the correctness of the obtained molecular formulas, for example, by calculating the molar mass.

Closure (8 - 10 minutes)

1. Group Discussion (3 - 4 minutes): The teacher should facilitate a group discussion with all students to share and discuss the solutions or conclusions reached by each group during the hands-on activities. This is an opportunity for students to learn from each other, clarify doubts, and reflect on the problem-solving processes. The teacher should act as a mediator, ensuring that all students have a chance to speak and that the discussion remains focused on the learning objectives.

   • Facilitation: The teacher should ask each group what they discovered during the activity and how they arrived at that conclusion. It is important for the teacher to ask open-ended questions that encourage students to explain their reasoning and justify their answers. The teacher should also encourage students to ask each other questions and offer constructive feedback.

2. Connecting to Theory (2 - 3 minutes): The teacher should then connect the hands-on activities to the theory. The teacher should explain how manipulating atoms and molecular formulas during the hands-on activities directly relates to determining molecular formula in theory. The teacher should also highlight the role of empirical formula and molar mass in determining molecular formula and how these concepts were applied during the hands-on activities.

   • Example: The teacher could explain that during the "Building Formulas" activity, students were essentially determining the molecular formula of a substance from its empirical formula. The teacher could also explain that during the "Determining Molecular Formulas" activity, students were applying the concept of molar mass to determine the multiplication factor that transforms the empirical formula into the molecular formula.

3. Final Reflection (2 - 3 minutes): Finally, the teacher should ask students to reflect individually on what they learned in the lesson. The teacher should ask questions that encourage students to think about the most important concepts, identify any difficulties they may still have, and plan what they will do to solidify their learning. The teacher should give students a minute to think silently and then ask them to share their reflections.

   • Reflection Questions:

     1. What was the most important concept you learned today?
     2. What questions do you still have?
     3. What do you plan to do to solidify what you learned today?

   • Facilitation: The teacher should ask a few students to share their answers with the class. The teacher should listen attentively, praise insightful answers, and provide constructive feedback for answers that need more clarification. The teacher should also reinforce the importance of independent study and practice for solidifying learning.

By the end of this stage, students should have a clear understanding of the concept of molecular formula and how to calculate it, as well as have developed problem-solving and critical-thinking skills. They should also be able to identify areas where they still have difficulties and plan what they will do to overcome them.

Conclusion (5 - 7 minutes)

1. Summary and Recap (2 - 3 minutes): The teacher should begin the conclusion of the lesson by reinforcing the main points covered during the lesson. This includes the definition of molecular formula, the difference between empirical formula and molecular formula, and the importance of molar mass and the periodic table in determining molecular formula. The teacher could use a visual summary, such as a diagram or a slide presentation, to reinforce the concepts and aid student comprehension.

2. Theory-Practice Connection (1 - 2 minutes): The teacher should then explain how the lesson connected theory and practice. The teacher could highlight how the hands-on activities, such as "Building Formulas" and "Determining Molecular Formulas," allowed students to apply the theoretical concepts in a concrete and meaningful way. The teacher should reinforce that understanding the theory is essential for effective problem-solving in practical situations.

3. Supplemental Materials (1 - 2 minutes): The teacher should suggest additional study materials for students who wish to explore the lesson topic further. This could include textbook chapters, educational videos, chemistry websites, and online practice exercises. The teacher should encourage students to explore these materials independently and seek the teacher for clarification of any questions that may arise.

4. Relevance of the Topic (1 minute): Finally, the teacher should reiterate the importance of determining molecular formula in everyday life and in various fields of study and work. The teacher could cite real-world examples, such as drug manufacturing, plastics production, and forensic analysis, to illustrate how the knowledge gained in the lesson is relevant and applicable. The teacher should encourage students to see chemistry as a practical and relevant science in their daily lives and to continue exploring and questioning the world around them from a chemical perspective.

By the end of this stage, students should have solidified their understanding of determining molecular formula, gained an appreciation for how theory applies in practice, and have a clear view of the relevance of the topic to everyday life and science in general.