Objectives (5 - 10 minutes)

1. Understand the concept of an atom and its importance in the formation of everything that exists in the universe.
2. Identify the main components of an atom, including protons, electrons, and neutrons, and their characteristics.
3. Recognize the basic structure of an atom, including the nucleus and the electron cloud, and how electrons move in this electron cloud.

Secondary Objectives:

• Stimulate curiosity and scientific investigation on the subject, encouraging students to seek more information.
• Develop the ability to analyze and synthesize the subject, allowing students to establish connections between the concept of an atom and other science topics.
• Promote active student participation in the class through discussions and practical activities.

Introduction (10 - 15 minutes)

1. Review of previous contents: The teacher should start the class by briefly reviewing the concepts of matter and subatomic particles (protons, electrons, and neutrons) that were learned in previous classes. This review serves to prepare the ground for the new topic, which is the atom. (3 - 5 minutes)

2. Problem situation: The teacher can propose two questions to instigate students' curiosity and spark interest in the subject:

   • Why do different types of matter have different properties?
   • If matter is composed of subatomic particles, how do these particles organize to form the variety of substances we see around us? (3 - 5 minutes)

3. Contextualization: The teacher should explain that the atom is the basic unit that makes up all matter and that its study is essential for us to understand how the world around us works, from the properties of the materials we use to the chemical processes that occur in our bodies. For example, the importance of knowledge about atoms in medicine (e.g., in radiotherapy) and technology (e.g., in the manufacturing of computer chips) can be highlighted. (2 - 3 minutes)

4. Introduction to the topic: The teacher should present the history of the Development of the atom concept, from the early ideas of Greek philosophers to the modern formulation. For example, the contribution of Democritus, who first proposed the idea that matter was composed of indivisible particles called atoms, and the subsequent discovery of subatomic particles by scientists like J.J. Thomson and Ernest Rutherford can be mentioned. (2 - 3 minutes)

5. Engaging students' attention: To capture students' interest, the teacher can share some curiosities about atoms, such as the fact that, despite being incredibly small, they are composed of a huge amount of empty space (for example, if a hydrogen atom were the size of a classroom, the nucleus would be the size of a grain of sand in the center) and that, although there are more than 100 different types of atoms, most of the matter we interact with daily is composed of only a few types. (2 - 3 minutes)

Development (20 - 25 minutes)

1. Atom theory: The teacher should start the theoretical part of the class by explaining that the atom is the smallest unit of a chemical element that still retains the properties of that element. (3 - 5 minutes)

   • The teacher should explain that there are more than 100 different types of atoms, each with a different number of protons, electrons, and neutrons. These different types of atoms are called chemical elements and are organized in the periodic table.

   • The teacher should discuss the basic structure of an atom, which consists of a central nucleus, where the protons and neutrons are, and an electron cloud around the nucleus, where the electrons move.

2. Subatomic particles: Next, the teacher should explain the characteristics and location of the three main subatomic particles: protons, electrons, and neutrons. (5 - 7 minutes)

   • Protons: The teacher should explain that protons are positively charged particles found in the nucleus of the atom. Each chemical element has a specific number of protons, which determines its place in the periodic table.

   • Electrons: The teacher should explain that electrons are negatively charged particles that orbit the nucleus of the atom in the electron cloud. The number of electrons is equal to the number of protons in a neutral atom.

   • Neutrons: The teacher should explain that neutrons are neutral particles found in the nucleus of the atom. They help keep the protons together in the nucleus but do not affect the chemical properties of the element.

3. Bohr model: The teacher should present the Bohr model, which describes the location of electrons in the electron cloud. (5 - 7 minutes)

   • The teacher should explain that, according to the Bohr model, electrons move in orbits around the nucleus in discrete energy levels. Each orbit has a fixed amount of energy, and electrons can jump from one orbit to another by absorbing or emitting energy in the form of light photons.

   • The teacher should discuss the concept of electron shells, which are the different orbits that electrons can occupy. The first shell, the closest to the nucleus, can hold up to 2 electrons, the second shell up to 8 electrons, and so on.

4. Atomic number and mass number: The teacher should explain the meaning of the atomic number (Z) and the mass number (A) and how they are used to describe an atom. (2 - 3 minutes)

   • The atomic number is equal to the number of protons in an atom and determines the chemical element.

   • The mass number is the sum of the number of protons and neutrons in an atom.

5. Consolidation exercises: To consolidate learning, the teacher should propose some consolidation exercises, such as identifying the number of protons, electrons, and neutrons in an atom based on its electronic configuration or locating them in the periodic table. (3 - 5 minutes)

Return (10 - 15 minutes)

1. Group discussion (5 - 7 minutes): The teacher should promote a group discussion about what was learned in the class. Students should be encouraged to share their insights, doubts, and questions that arose during the class. The teacher should guide the discussion, ensuring that all key points are addressed and doubts are clarified. This is an opportunity for students to consolidate their learning and for the teacher to assess the class's understanding of the topic.

2. Connection to the real world (3 - 5 minutes): The teacher should propose that students reflect on how the concept of the atom connects to the real world. Some points for discussion may include:

   • Technological applications: How is knowledge about atoms applied in the technology we use daily? (e.g., in the manufacturing of computer chips, in nuclear energy production, etc.)

   • Relevance to health: How is knowledge about atoms relevant to health and medicine? (e.g., in radiotherapy, in the production of radioisotopes for medical diagnosis, etc.)

   • Importance in everyday life: How can knowledge about atoms help us better understand the world around us? (e.g., why different types of materials have different properties, how chemical reactions occur, etc.)

3. Individual reflection (2 - 3 minutes): Finally, the teacher should propose that students reflect individually on what they learned in the class. Some points for reflection may include:

   • What was the most important concept you learned today?

   • What questions have not been answered yet? (These questions can be discussed in the next class or can serve as the basis for students' individual research.)

   • How can you apply what you learned today in your daily life or in other subjects?

This Return stage is crucial to consolidate learning, encourage reflection and connection of knowledge to the real world, and identify any gaps in students' understanding that need to be addressed in future classes.

Conclusion (5 - 10 minutes)

1. Summary of key points (2 - 3 minutes): The teacher should recap the key points of the class, reinforcing the concept of the atom as the smallest unit of a chemical element and the basic structure of an atom, including the nucleus, the electron cloud, and the subatomic particles (protons, electrons, and neutrons). Additionally, the Bohr model and the importance of the atomic number and mass number in describing an atom should be recalled.

2. Connection between theory, practice, and applications (1 - 2 minutes): The teacher should reinforce how the class connected theory, practice, and applications. This can be done, for example, by highlighting how the theoretical explanation of atoms and their characteristics was supported by practical activities, such as solving exercises. Additionally, the practical applications of the atom concept, such as in technology and medicine, should be remembered.

3. Extra materials (1 - 2 minutes): The teacher should suggest extra materials to deepen students' understanding of the topic. This may include books, websites, videos, and documentaries that address the topic in more detail or present interesting applications of the atom concept. For example, the teacher may suggest that students watch a video about the history of the atom, read an article about the discovery of subatomic particles, or explore an online simulator that allows manipulating virtual atoms.

4. Relevance of the topic (1 - 2 minutes): Finally, the teacher should emphasize the importance of the topic for students' daily lives and for the world in general. It should be reinforced that the atom is the fundamental unit of matter and, therefore, the study of atoms is crucial for us to understand the world around us. For example, it can be mentioned that knowledge about atoms is essential for science and technology, for medicine, for industry, and even for our understanding of ourselves as human beings (e.g., genetics, which is the study of heredity, is based on how atoms organize to form biological molecules and structures).