Sulfur tetrafluoride (SF₄) reacts slowly with O₂ to form sulfur tetrafluoride monoxide (OSF₄) according to the following unbalanced reaction: SF₄(g) + O₂(g) → OSF₄(g). The O atom and the four F atoms in OSF₄ are bonded to a central S atom. (d) Determine the electron-domain geometry of OSF₄, and write two possible molecular geometries for the molecule based on this electron-domain geometry. (e) For each of the molecules you drew in part (d), state how many fluorines are equatorial and how many are axial.

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To determine the electron-domain geometry of OSF₄, first count the total number of electron domains around the central sulfur atom. OSF₄ has one oxygen atom and four fluorine atoms bonded to sulfur, plus one lone pair of electrons on sulfur. This results in six electron domains.

The electron-domain geometry for a molecule with six electron domains is octahedral. This geometry considers both bonding and non-bonding electron pairs.

Based on the octahedral electron-domain geometry, two possible molecular geometries for OSF₄ can be derived: square pyramidal and seesaw. These geometries depend on the arrangement of the lone pair and bonded atoms.

In the square pyramidal geometry, the lone pair occupies one of the equatorial positions, resulting in four fluorine atoms in the equatorial plane and one oxygen atom in the axial position.

In the seesaw geometry, the lone pair occupies one of the equatorial positions, resulting in two fluorine atoms in the equatorial plane and two fluorine atoms in the axial positions, with the oxygen atom also in an equatorial position.

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 is determined by the number of electron domains, which can include single bonds, double bonds, triple bonds, and lone pairs. For example, a central atom with four electron domains will have a tetrahedral electron-domain geometry.

Molecular Geometry

Molecular geometry describes the three-dimensional arrangement of atoms in a molecule, which can differ from the electron-domain geometry due to the presence of lone pairs. The molecular geometry is influenced by the repulsion between electron domains, leading to specific shapes such as trigonal bipyramidal or seesaw. Understanding the distinction between electron-domain and molecular geometry is crucial for predicting the shape of a molecule.

Equatorial and Axial Positions

In molecules with trigonal bipyramidal geometry, such as SF₄, the positions of atoms can be classified as equatorial or axial. Equatorial positions are located in the plane of the molecule and are typically occupied by larger substituents to minimize steric hindrance, while axial positions are oriented perpendicular to this plane. Identifying which fluorine atoms occupy these positions is essential for understanding the molecular structure and its properties.

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Equatorial vs. Axial Positions

Related Practice

Textbook Question

The energy-level diagram in Figure 9.36 shows that the sideways overlap of a pair of p orbitals produces two molecular orbitals, one bonding and one antibonding. In ethylene there is a pair of electrons in the bonding π orbital between the two carbons. Absorption of a photon of the appropriate wavelength can result in promotion of one of the bonding electrons from the p2p to the p*2p molecular orbital. (b) Assuming this electronic transition corresponds to the HOMO-LUMO transition, what is the LUMO in ethylene?

Textbook Question

The energy-level diagram in Figure 9.36 shows that the sideways overlap of a pair of p orbitals produces two molecular orbitals, one bonding and one antibonding. In ethylene there is a pair of electrons in the bonding π orbital between the two carbons. Absorption of a photon of the appropriate wavelength can result in promotion of one of the bonding electrons from the p2p to the p*2p molecular orbital. (c) Is the C¬C bond in ethylene stronger or weaker in the excited state than in the ground state? Why?

Textbook Question

Sulfur tetrafluoride 1SF42 reacts slowly with O2 to form sulfur tetrafluoride monoxide 1OSF42 according to the following unbalanced reaction: SF41g2 + O21g2¡OSF41g2 The O atom and the four F atoms in OSF4 are bonded to a central S atom. (a) Balance the equation.

Textbook Question

Sulfur tetrafluoride (SF₄) reacts slowly with O₂ to form sulfur tetrafluoride monoxide (OSF₄) according to the following unbalanced reaction: SF₄(g) + O₂(g) → OSF₄(g) The O atom and the four F atoms in OSF₄ are bonded to a central S atom. (b) Write a Lewis structure of OSF₄ in which the formal charges of all atoms are zero.

Textbook Question

Sulfur tetrafluoride (SF₄) reacts slowly with O₂ to form sulfur tetrafluoride monoxide (OSF₄) according to the following unbalanced reaction: SF₄(g) + O₂(g) → OSF₄(g) The O atom and the four F atoms in OSF₄ are bonded to a central S atom. (c) Use average bond enthalpies (Table 8.3) to estimate the enthalpy of the reaction. Is it endothermic or exothermic?