What is the difference between Electron Domain Geometry & Molecular Geometry

Summary

This video explains the distinction between Electron Domain Geometry (EDG) and Molecular Geometry (MG) in chemistry. EDG considers both bonds and lone pairs around a central atom, describing the arrangement of all electron domains. MG, on the other hand, focuses solely on the arrangement of bonds, ignoring lone pairs. Through examples like NH3, H2O, and CH4, the video illustrates how the number of electron domains and lone pairs determine these geometries. The video emphasizes how understanding both EDG and MG helps predict molecular shapes and bond angles in different molecules.

Takeaways

• 😀 Electron Domain Geometry (EDG) describes the arrangement of bonds and lone pairs based on the number of electron domains.
• 😀 Molecular Geometry (MG) focuses only on the arrangement of bonds, ignoring lone pairs, and is determined by both the number of electron domains and lone pairs.
• 😀 VSEPR (Valence Shell Electron Pair Repulsion) structures help predict the shapes and bond angles of molecules based on electron domain geometry.
• 😀 If a molecule has a certain number of electron domains, the EDG is determined by that number, regardless of lone pairs present.
• 😀 Molecular geometry ignores lone pairs, and is only concerned with the arrangement of bonds between atoms.
• 😀 When the number of lone pairs is zero, the molecular geometry and electron domain geometry will be identical.
• 😀 The molecular geometry of NH3 (ammonia) is trigonal pyramidal because it has four electron domains and one lone pair.
• 😀 The electron domain geometry of NH3 is tetrahedral because it has four electron domains, including lone pairs.
• 😀 The molecular geometry of water (H2O) is bent (angular) because of two lone pairs and four electron domains.
• 😀 The electron domain geometry of water is tetrahedral because it has four electron domains, including lone pairs.
• 😀 A molecule with four electron domains and no lone pairs, like CH4 (methane), will have a tetrahedral electron domain geometry and molecular geometry.

Q & A

What is the difference between electron domain geometry (EDG) and molecular geometry (MG)?

Electron domain geometry (EDG) describes the arrangement of all electron domains, including bonds and lone pairs. It is determined by the total number of electron domains. Molecular geometry (MG), on the other hand, focuses only on the arrangement of bonds, ignoring lone pairs. MG is determined by both the number of electron domains and the number of lone pairs.

Why do we ignore lone pairs when determining molecular geometry?

Lone pairs are ignored in molecular geometry because they don't directly affect the shape of the molecule. The molecular geometry focuses on the spatial arrangement of the atoms (bonds), not the lone pairs, which only affect the electron domain geometry.

How is the electron domain geometry of a molecule determined?

The electron domain geometry is determined by the number of electron domains around a central atom. This includes both bonding pairs of electrons and lone pairs of electrons. The arrangement is based on minimizing electron-electron repulsion, and each different number of electron domains has a specific geometry, such as linear, trigonal planar, tetrahedral, etc.

What is the molecular geometry of a molecule with four electron domains and one lone pair?

A molecule with four electron domains and one lone pair has a trigonal pyramidal molecular geometry. The lone pair affects the shape, causing the bonds to be pushed downward into a pyramid shape.

How does the presence of lone pairs affect the electron domain geometry?

Lone pairs influence the electron domain geometry by occupying space and contributing to the total number of electron domains. However, they do not affect the molecular geometry directly, since molecular geometry only considers the arrangement of bonds.

Why is the molecular geometry of NH3 (ammonia) trigonal pyramidal?

NH3 has four electron domains, one of which is a lone pair. When considering the bonds only (ignoring the lone pair), the molecule adopts a trigonal pyramidal molecular geometry, with the three bonding atoms at the vertices of a pyramid.

What is the electron domain geometry of H2O (water)?

The electron domain geometry of water is tetrahedral because it has four electron domains (two bonds and two lone pairs) around the central oxygen atom. However, the molecular geometry is bent or angular, as it ignores the lone pairs.

What is the molecular geometry of CH4 (methane)?

The molecular geometry of CH4 is tetrahedral because it has four electron domains (all bonding) and no lone pairs. This results in an equal, symmetric distribution of bonds.

What happens to the electron domain and molecular geometry when there are no lone pairs?

When there are no lone pairs, the electron domain geometry and molecular geometry are the same. For example, a molecule with four electron domains and no lone pairs will have both a tetrahedral electron domain geometry and a tetrahedral molecular geometry.

In the case of SO2, how do you determine its electron domain and molecular geometry?

SO2 has three electron domains (two bonds and one lone pair). The electron domain geometry is trigonal planar, considering all electron domains. The molecular geometry is bent or angular, as it ignores the lone pair and focuses on the bonding atoms.