Chapter 7: Problem 17
Write Lewis structures for \(\mathrm{XeOF}_{2}\) and \(\mathrm{ClOF}_{3}\). Use VSEPR theory to predict the electron-region and molecular geometries of these molecules, and note any differences between these geometries.
Short Answer
Expert verified
\(\mathrm{XeOF}_2\) and \(\mathrm{ClOF}_3\) are both "T-shaped" molecularly, despite their "trigonal bipyramidal" electron-region geometries.
Step by step solution
01
Count the Valence Electrons
Start by counting the total number of valence electrons for each molecule. For \(\mathrm{XeOF}_2\), xenon (Xe) has 8 valence electrons, oxygen (O) has 6, and each fluorine (F) has 7, giving a total of \(8 + 6 + 2 \times 7 = 28\) electrons. For \(\mathrm{ClOF}_3\), chlorine (Cl) has 7 valence electrons, oxygen (O) has 6, and each fluorine (F) has 7, giving a total of \(7 + 6 + 3 \times 7 = 34\) electrons.
02
Draw the Lewis Structures
For \(\mathrm{XeOF}_2\), place Xe in the center with one O and two F atoms bonded to it; arrange the remaining electrons to complete the octets of O and F, and assign lone pairs on Xe. For \(\mathrm{ClOF}_3\), place Cl in the center with one O and three F atoms bonded to it; complete the octets of O and F, and assign lone pairs on Cl. Xe and Cl can expand their octet because they are in period 5 and 3, respectively.
03
Determine the Electron-Region Geometries
For \(\mathrm{XeOF}_2\), using VSEPR, find the electron-region geometry by considering all lone pairs and bonds around Xe. With 5 electron regions (2 bonding and 3 lone pairs), the geometry is "trigonal bipyramidal". For \(\mathrm{ClOF}_3\), it also has 5 regions (3 bonding and 2 lone pairs), making the electron-region geometry "trigonal bipyramidal" as well.
04
Determine the Molecular Geometries
For \(\mathrm{XeOF}_2\), the molecular geometry is "T-shaped" due to the presence of 2 bonding pairs and 3 lone pairs. For \(\mathrm{ClOF}_3\), with 3 bonding pairs and 2 lone pairs, the molecular geometry is "T-shaped" too.
05
Compare Electron-Region and Molecular Geometries
The electron-region geometries for both molecules differ from their molecular geometries. While the electron-region geometry is "trigonal bipyramidal" for both, the lone pairs affect the shape, resulting in a "T-shaped" molecular geometry for both \(\mathrm{XeOF}_2\) and \(\mathrm{ClOF}_3\).
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Key Concepts
These are the key concepts you need to understand to accurately answer the question.
VSEPR Theory
Valence Shell Electron Pair Repulsion (VSEPR) theory helps us understand the shapes of molecules. It's based on the idea that electron pairs around a central atom repel each other. This leads the pairs to arrange themselves as far apart as possible.
In practice, this means counting all the electron regions — bonded pairs and lone pairs — around the central atom. This count determines the electron-region geometry.
In practice, this means counting all the electron regions — bonded pairs and lone pairs — around the central atom. This count determines the electron-region geometry.
- For example, if there are five electron regions, the geometry is termed "trigonal bipyramidal."
Molecular Geometry
Molecular geometry describes the actual shape of a molecule. It focuses on the positions of the atoms, not the lone pairs.
Even though lone pairs are invisible in these models, they push bonding pairs closer together, changing the shape.
Even though lone pairs are invisible in these models, they push bonding pairs closer together, changing the shape.
- For instance, in both \( \mathrm{XeOF}_2 \) and \( \mathrm{ClOF}_3 \), the electron-region geometry is trigonal bipyramidal.
- But because of the lone pairs, the "real" shape that includes the bonded atoms is T-shaped.
Valence Electrons
Valence electrons are the outermost electrons of an atom, crucial for forming chemical bonds. They determine how atoms interact and bind with each other.
To count valence electrons, check the group number of each element in the periodic table.
To count valence electrons, check the group number of each element in the periodic table.
- For \( \mathrm{XeOF}_2 \), xenon contributes 8, oxygen 6, and each fluorine 7, totaling 28.
- For \( \mathrm{ClOF}_3 \), chlorine has 7, oxygen 6, and each fluorine 7, adding up to 34.
Electron-Region Geometry
Electron-region geometry is determined by the total count of lone pairs and bonding pairs around the central atom. This concept is crucial for predicting the overall 3D arrangement of electron pairs.
In both \( \mathrm{XeOF}_2 \) and \( \mathrm{ClOF}_3 \), the electron-region geometry is trigonal bipyramidal because each has five regions around the central atom.
In both \( \mathrm{XeOF}_2 \) and \( \mathrm{ClOF}_3 \), the electron-region geometry is trigonal bipyramidal because each has five regions around the central atom.
- These regions include all the bonds and lone pairs.