Objectives (5 - 7 minutes)

1. Understanding the concept of atomic mass: Students should be able to understand what atomic mass is, how it is determined, and what unit is used to express it.

2. Calculating the average atomic mass: Students should learn how to calculate the average atomic mass of an element based on its isotopic abundances and relative atomic masses.

3. Applying the concept of atomic mass in practical problems: Students should be able to apply the concept of atomic mass in real situations, such as determining the quantity of an element in a sample.

Secondary objectives:

• Development of problem-solving skills: Through the application of the concept of atomic mass in practical problems, students should develop their problem-solving skills.

• Enhancement of critical thinking skills: By learning about atomic mass and its application, students should enhance their critical thinking skills, being able to analyze and interpret information more effectively.

Introduction (10 - 15 minutes)

1. Review of previous content: The teacher should start the lesson by reviewing the concepts of atom, isotopes, and the structure of the atom (nucleus, protons, neutrons, and electrons). This review is essential for students to better understand the concept of atomic mass. (3 - 5 minutes)

2. Problem situation: The teacher can propose two problem situations to arouse the interest and curiosity of the students. The first one could be: "How do scientists determine the mass of particles as small as atoms?" And the second: "Imagine you have two samples of the same element, one with lighter atoms and the other with heavier atoms. How could you calculate the average mass of these atoms?" (3 - 5 minutes)

3. Contextualization: The teacher should contextualize the importance of studying atomic mass, explaining that this concept is fundamental for various areas of science, such as chemistry, physics, and biology. For example, atomic mass is used to determine the quantity of an element in a sample, calculating the amount of substance or moles. Additionally, it is used to understand and predict the behavior of atoms in chemical reactions. (2 - 3 minutes)

4. Capturing students' attention: To arouse students' curiosity, the teacher can share two curiosities. The first one is that the atomic mass of carbon is used as a reference to calculate the atomic mass of all other elements, with carbon-12 chosen as the standard. And the second is that the periodic table, which is one of the main study tools in chemistry, organizes the elements in increasing order of atomic mass. (2 - 3 minutes)

Development (20 - 25 minutes)

1. Activity "Building Atoms" (10 - 15 minutes)

   • Materials needed: Cardboard, colored pens, stickers of different colors, scissors, glue.

   • Activity description: Students, divided into groups of up to 5, must build an atom of an element from the periodic table using the available materials. They should choose the element and then research its characteristics, including its atomic mass. Then, they should draw the atom on the cardboard, indicating the quantity of protons, neutrons, and electrons according to the chosen element. Stickers of different colors can be used to represent each subatomic particle. Finally, they should calculate the atomic mass of the atom they built, based on the masses of the subatomic particles and their isotopic abundances.

   • Step by step:

     1. Choose an element from the periodic table.
     2. Research the quantity of protons, neutrons, and electrons of that element.
     3. Draw the atom on the cardboard, using stickers to represent the subatomic particles.
     4. Calculate the atomic mass of the atom, based on the masses of the subatomic particles and their isotopic abundances.

2. Activity "Hunting for Atomic Mass" (10 - 15 minutes)

   • Materials needed: List of elements from the periodic table, calculator, paper, and pen.

   • Activity description: In this activity, students must calculate the average atomic mass of different elements. The teacher will distribute the list of elements to each group of students. They should research the relative atomic masses of the elements on the periodic table and calculate the average atomic mass based on the isotopic abundance of each isotope of the element. The group that correctly calculates the average atomic mass for the majority of the elements on the list will be the winner.

   • Step by step:

     1. Receive the list of elements.
     2. Research the relative atomic masses of the elements.
     3. Calculate the average atomic mass of each element.
     4. Compare the answers with those of other groups.
     5. The group with the most correct answers wins the activity.

3. Discussion and Reflection (5 - 10 minutes)

   • Activity description: After completing the activities, the teacher should promote a discussion in the classroom, allowing students to share their experiences, difficulties, and learnings. The teacher can ask questions to encourage students' reflection, such as: "What did you learn from the atom-building activity?" or "What were the biggest difficulties encountered when calculating the average atomic mass of the elements?" The teacher should clarify any doubts students may have and reinforce the concepts learned.

Return (10 - 12 minutes)

1. Group Discussion (3 - 5 minutes)

   • Activity description: The teacher should promote a group discussion, where each team shares their solutions or conclusions from the activities carried out. Each group will have a maximum of 3 minutes to present. The teacher should guide the discussion by asking questions that encourage students to explain the reasoning behind their solutions.

   • Step by step:

     1. Each group will have the opportunity to present their solutions or conclusions from the activities carried out.
     2. The teacher should guide the discussion by asking questions that encourage students to explain the reasoning behind their solutions.
     3. Other students should pay attention to their classmates' presentations and ask questions if necessary.

2. Connection to Theory (2 - 3 minutes)

   • Activity description: After the presentations, the teacher should make the connection between the activities carried out and the theory discussed in the Introduction of the lesson. The teacher should highlight how the activities illustrated or applied the theoretical concepts of atomic mass and average atomic mass.

   • Step by step:

     1. The teacher should briefly review the concepts of atomic mass and average atomic mass.
     2. The teacher should highlight how the activities carried out illustrated or applied these concepts.
     3. Students should be encouraged to make connections on their own, reflecting on how the activities helped solidify their understanding of the concepts.

3. Final Reflection (2 - 3 minutes)

   • Activity description: To conclude the lesson, the teacher should propose that students reflect individually on what they have learned. The teacher can ask questions that encourage students to think about the importance of the concept of atomic mass and how they can apply it in everyday situations or in other disciplines.

   • Step by step:

     1. The teacher should propose that students reflect individually on what they learned in the lesson.
     2. The teacher should ask questions that encourage students to think about the importance of the concept of atomic mass and how they can apply it in everyday situations or in other disciplines.
     3. Students should have a minute to think and then will have the opportunity to share their reflections, if they wish.

4. Teacher's Feedback (1 minute)

   • Activity description: The teacher should give brief feedback on the students' participation and performance during the lesson. The teacher should praise the students' effort and dedication and highlight the strengths of the class. Additionally, the teacher should identify any areas that may need further review or practice.

   • Step by step:

     1. The teacher should praise the students' effort and dedication.
     2. The teacher should highlight the strengths of the class.
     3. The teacher should identify any areas that may need further review or practice.
     4. The teacher should encourage students to continue practicing and studying the concept of atomic mass.

Conclusion (3 - 5 minutes)

1. Summary of Contents:

   • The teacher should recap the main points covered during the lesson, emphasizing the definition of atomic mass, the importance of carbon-12 as a reference standard, and the formula for calculating the average atomic mass.

   • The practical activities carried out should be recalled and how they helped consolidate students' understanding of the concept of atomic mass.

2. Connection between Theory, Practice, and Applications:

   • The teacher should emphasize how the lesson connected theory (definition of atomic mass and calculation of average atomic mass) with practice (activities "Building Atoms" and "Hunting for Atomic Mass").

   • It should also be highlighted how this knowledge can be applied in real situations, such as in determining the quantity of an element in a sample, or in predicting the behavior of atoms in chemical reactions.

3. Additional Materials:

   • The teacher should suggest extra materials for students who wish to deepen their knowledge on the subject. This may include additional readings, educational videos, online simulators, or additional exercises.

   • Examples of additional materials could be: the chapter on atomic mass from a chemistry book, an explanatory video on calculating the average atomic mass, an online simulator that allows students to build different atoms and calculate their atomic masses, or a set of reinforcement exercises.

4. Importance of the Subject:

   • Finally, the teacher should emphasize the relevance of the subject covered for everyday life and for other disciplines. For example, it should be explained that atomic mass is used in various applications of chemistry, physics, and biology, such as in determining quantities of substances, predicting chemical reactions, or studying radioactive isotopes.

   • The teacher can also ask students how they think what they learned can be useful in their lives, encouraging them to make connections between theory and practice.