Contextualization
Molecular geometry is a field in chemistry that studies the shapes of molecules. This study is crucial in order to understand many fundamental aspects of chemistry, including chemical bond formation, properties of substances, chemical reactions, and the structure of new compounds. Molecular geometry can be determined by analyzing the electronic distribution of the atoms, and there are some major types: linear, trigonal, tetrahedral, pyramidal, and angular.
To understand molecular geometry is to understand a map of molecules. In the same way that a map helps us to find our way in an unknown location, molecular geometry helps us to understand how the atoms will organize in space, and this organization has a direct influence on the chemical and physical properties of the compounds.
Molecular geometry is linked with the Octet Rule, which provides us a way to understand the formation of molecules and how the atoms share electrons to form covalent bonds. The Valence Shell Electron Pair Repulsion (VSEPR) Theory is also an important principle that will be used in this project, because it allows us to predict the geometry of molecules.
Importance of Molecular Geometry
The comprehension of molecular geometry is an important topic, as it influences the physical and chemical properties of compounds, such as melting and boiling point, solubility, and reactivity, among others. This means that this field of knowledge is crucial not only for chemistry, but also for professionals in other areas such as Medicine, Pharmacy, Engineering, Biology, and so on.
The knowledge of molecular geometry is essential to understand how drugs interact with the human body, how materials are formed and what are their properties, besides being crucial to develop new compounds and materials. Therefore, to study molecular geometry is not only to gain theoretical knowledge, but also a practical skill that can be applied in different fields of science.
Practical Activity: Shaping Molecules
Objective
Students will use commonly found materials (jellybeans and toothpicks) to build three-dimensional models of molecules, thus visualizing their molecular geometries. Besides, they will investigate the properties of these molecules and their relation to their geometry.
Students should have a practical and intuitive understanding, after completing the project, about the way the molecular geometry affects the properties of compounds. Also, they will have the opportunity to physically handle molecular models and investigate their characteristics.
Detailed Project Overview
This activity is divided into three main parts: research and preparation, model building, analysis, and report.
1. Research and preparation: In this part of the project, each group must research and select five different molecules to build. The chosen molecules must include at least one example of each type of molecular geometry (linear, trigonal, tetrahedral, pyramidal, and angular). Also, the group must research and record the properties of the chosen molecules, including: melting point, boiling point, polarity, reactivity, and other relevant properties.
2. Model Building: Students will build physical models of the molecules researched, using the toothpicks and jellybeans. The toothpicks will represent the chemical bonds between atoms and the jellybeans the atoms. The teams should document this process taking pictures and writing a detailed description of it.
3. Analysis and report: Once the models are built, students will analyze each molecule and relate the researched properties (step 1) with the observed geometry of the constructed models. The objective here is to identify the relation between the structure and properties of molecules. Also, students should reflect about their experience working as a team, discussing how their collaboration contributed to the project.
Necessary materials:
- Toothpicks
- Different colors of jellybeans (different colors will represent different types of atoms)
- Research materials (books, internet access, etc.)
- Camera (to document the activity)
- Writing materials (for the report)
Step by step detailed procedure to carry out the activity:
- Divide the class into groups of 3-5 students each.
- Each group researches and selects the molecules (step 1 in the previous section).
- Using the indicated materials, each group builds the molecular models (step 2).
- Each group performs an analysis of their built molecules, relating their molecular geometry to the researched properties (step 3).
- Finally, each group prepares a report documenting the whole process, including pictures, discussions, and conclusions.
Project submission:
The project should be submitted in the form of a report, that must contain the following items:
- Introduction: Contextualization of the theme, objectives of the activity, and practical applicability of the knowledge about molecular geometry.
- Development: A detailed discussion about the process of selecting the molecules, building the models and the analysis of each molecule. The methodology of the activity must also be detailed here.
- Conclusions: Discussion about the obtained results and the conclusions regarding the relationship between molecular geometry and the properties of compounds. It must also include a reflection about teamwork.
- Bibliography: A list of all consulted references used to complete the project.
Students should write the report in a clear and organized way. Besides the topics addressed before, the reports must include pictures that document the process of the practical activity.
