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Ch.9 - Molecular Geometry and Bonding Theories
All textbooksBrown 14th EditionCh.9 - Molecular Geometry and Bonding TheoriesProblem 25a
Chapter 9, Problem 25a

Give the electron-domain and molecular geometries for the following molecules and ions: (a) BeF2

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Step 1: Determine the central atom in the molecule. In BeF2, the central atom is Beryllium (Be).
Step 2: Draw the Lewis structure of the molecule. In BeF2, Beryllium forms single bonds with two Fluorine atoms. Beryllium has 2 valence electrons, all of which are used in bonding, and Fluorine has 7 valence electrons, 6 of which are used in forming three lone pairs, and one is used in bonding.
Step 3: Determine the electron-domain geometry based on the number of electron domains (regions of high electron density). In BeF2, there are two electron domains (two single bonds), so the electron-domain geometry is linear.
Step 4: Determine the molecular geometry based on the number of bonding domains and lone pairs on the central atom. In BeF2, there are two bonding domains and no lone pairs on the central atom, so the molecular geometry is also linear.
Step 5: Summarize the electron-domain and molecular geometries. For BeF2, both the electron-domain and molecular geometries are linear.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Electron-Domain Geometry

Electron-domain geometry refers to the spatial arrangement of all electron domains (bonding and lone pairs) around a central atom in a molecule. It helps predict the overall shape of the molecule based on the number of electron domains. For example, in BeF2, there are two bonding pairs and no lone pairs, leading to a linear electron-domain geometry.
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Molecular Geometry

Molecular geometry describes the three-dimensional arrangement of atoms in a molecule, considering only the positions of the nuclei of the atoms. It is influenced by the electron-domain geometry but focuses solely on the atoms, excluding lone pairs. In the case of BeF2, the molecular geometry is also linear, as the two fluorine atoms are positioned opposite each other.
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VSEPR Theory

Valence Shell Electron Pair Repulsion (VSEPR) theory is a model used to predict the geometry of individual molecules based on the repulsion between electron pairs in the valence shell of the central atom. According to VSEPR, electron pairs will arrange themselves to minimize repulsion, which helps determine both electron-domain and molecular geometries. This theory is essential for understanding the shapes of molecules like BeF2.
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