Question

The heavier halogens (Cl, Br, and I) form compounds in which the central halogen atom, \(X\), is bonded directly to oxygen and to fluorine. Several examples are known, including those with formulas of the type \(\mathrm{FXO}_{2}, \mathrm{FXO}_{3, \text { and } \mathrm{F}_{3} \mathrm{XO} . \text { The structures of these }}\) molecules are all consistent with the VSEPR model. Draw Lewis structures and predict the geometries of (a) chloryl fluoride, \(\mathrm{FClO}_{2}\); (b) perchloryl fluoride, \(\mathrm{FClO}_{3} ;(\mathrm{c}) \mathrm{F}_{3} \mathrm{ClO}\).

Short answer

The molecules FClO2, FClO3, and F3ClO all have chlorines as the central atom. They have trigonal pyramidal, tetrahedral, and tetrahedral geometries respectively, according to the VSEPR model. Note that the geometrical shape of a molecule does not depend on whether outer atoms are identical or different.

Step-by-step solution

Identify the Central Atom and Draw Lewis Structure

Identify the central atom. This is usually the atom that has the highest bonding capacity. Here, Chlorine (Cl) is the central atom for each molecule. Draw the Lewis structures for FClO2, FClO3, and F3ClO. In these Lewis structures, make sure to consider all the valence electrons and follow octet rule as per as possible.

Predict Geometries using VSEPR Model

Once the Lewis structure is completed, predict the 3-D geometrical arrangement of atoms in a molecule using the Valence Shell Electron Pair Repulsion Model. This model proposes that electron pairs will arrange themselves around the central atom to minimize repulsion.

Analyze the Molecule FClO2

For chloryl fluoride (FClO2), the central atom, Chlorine, is surrounded by three atoms and one lone pair. According to VSEPR model, this gives a trigonal pyramidal geometry.

Analyze the Molecule FClO3

For perchloryl fluoride (FClO3), the central atom, Chlorine, is surrounded by four atoms, with no lone pairs on the central atom. This gives a tetrahedral geometry according to VSEPR model.

Analyze the Molecule F3ClO

For F3ClO, the central atom, Chlorine, is surrounded by four atoms, with no lone pairs on the central atom. This gives a tetrahedral geometry according to VSEPR model.

Key concepts

Lewis Structures

Understanding Lewis structures is essential for predicting the shape of molecules and their chemical properties. These diagrams depict the bonds between atoms of a molecule as well as any lone pairs of electrons that may exist.

When drawing Lewis structures, we begin by counting the valence electrons available, which are the electrons in the outermost shell that are involved in bonding. Each bond between atoms will account for two shared electrons. We strive for each atom, especially the central one, to follow the octet rule, meaning it has eight electrons in its valence shell, whenever possible.

For halogen compounds like chloryl fluoride, perchloryl fluoride, and F3ClO, we place the halogen (Cl) in the center and distribute other atoms (F and O) around it, ensuring that we have the appropriate number of bonds and lone pairs to give each atom (especially the halogens) a complete octet—or as close to it as possible.

Molecular Geometry

The spatial arrangement of atoms within a molecule, known as molecular geometry, is determined by the interactions between bonding and non-bonding electron pairs in the valence shell of the central atom.

The VSEPR model is invaluable for predicting molecular geometry. It considers electron pairs—both shared (bonding) and unshared (lone pairs)—around a central atom and posits that these pairs will arrange themselves as far apart as possible to minimize repulsion. This arrangement dictates the molecule's shape.

Common Geometries

• Linear
• Trigonal planar
• Tetrahedral
• Trigonal bipyramidal
• Octahedral

Compounds like FClO2, FClO3, and F3ClO exhibit geometries ranging from trigonal pyramidal to tetrahedral due to the different arrangements of electron pairs around the chlorine.

Electron Pair Repulsion

The VSEPR model hinges on the concept of electron pair repulsion, a fundamental principle that helps explain the molecular shapes observed in halogen compounds like FClO2, FClO3, and F3ClO.

Electron pairs, whether they're involved in bonds or are non-bonding lone pairs, carry a negative charge. Because like charges repel, these pairs will automatically position themselves as far apart as possible in a three-dimensional space around the central atom. This repulsion affects the molecular geometry and leads to the arrangement that minimizes electron pair repulsion, ultimately defining the shape of the molecule.

Halogen Compounds

Halogen compounds, particularly those that involve a central halogen atom like chlorine bonded to different atoms such as oxygen and fluorine, exhibit a variety of molecular shapes due to their differing electron configurations and bond arrangements.

In the molecules FClO2, FClO3, and F3ClO, chlorine is the central atom and forms the pivot for the molecule's structure. As we can see in the exercise solutions, electrons shared in bonds and the presence of lone electron pairs contribute to diverse and specific molecular geometries predicted by the VSEPR model. These variations in structure influence the chemical reactivity and physical properties of each compound, illustrating the vast range of possibilities within halogen chemistry.