Ikatan Kimia (6) | Bentuk Molekul | Teori VSEPR | Teori Domain Elektron | Kimia Kelas X

Introduction

In this tutorial, we will explore how to predict molecular shapes using VSEPR (Valence Shell Electron Pair Repulsion) theory and the electron domain theory. This guide is particularly useful for high school chemistry students looking to enhance their understanding of molecular geometry. By following these steps, you can accurately determine the shape of various molecules based on their electron pairs.

Step 1: Understand Electron Pairs

Identify the types of electron pairs in a molecule

• Bonding pairs: Electrons that are shared between atoms (forming bonds).
• Lone pairs: Unshared or non-bonding electrons that belong to a single atom.
• Count the total number of bonding pairs and lone pairs around the central atom.

Step 2: Determine the Total Number of Electron Domains

• Electron domain: Any region where electrons are likely to be found, including bonding pairs and lone pairs.

Use the following formula to find the total number of electron domains

• Total Electron Domains = Number of Bonding Pairs + Number of Lone Pairs.
• For example, if a molecule has 3 bonding pairs and 1 lone pair, the total number of electron domains is 4.

Step 3: Apply VSEPR Theory

Use the total number of electron domains to predict the molecular shape

• 2 electron domains: Linear shape (180°)
• 3 electron domains: Trigonal planar shape (120°)
• 4 electron domains: Tetrahedral shape (109.5°)
• 5 electron domains: Trigonal bipyramidal shape (90° and 120°)
• 6 electron domains: Octahedral shape (90°)

Consider the effect of lone pairs on the shape

• Lone pairs take up more space than bonding pairs, which can alter the shape.

Step 4: Visualize the Molecular Shape

• Draw the Lewis structure of the molecule to visualize bonding and lone pairs.
• Use molecular modeling kits or software for a 3D representation if available.

Step 5: Practice with Examples

Apply the learned concepts to various molecules

Water (H₂O)

• 2 bonding pairs, 2 lone pairs = 4 electron domains → Bent shape.

Carbon dioxide (CO₂)

• 2 bonding pairs, 0 lone pairs = 2 electron domains → Linear shape.
• Analyze the shapes and confirm your predictions using VSEPR rules.

Conclusion

By understanding and applying VSEPR theory and the concept of electron domains, you can successfully predict the shapes of molecules. This skill is essential for further studies in chemistry and related fields. Keep practicing with different molecules to strengthen your grasp on molecular geometry. Happy learning!