Sulfur tetrafluoride \(\left(\mathrm{SF}_{4}\right)\) reacts slowly with \(\mathrm{O}_{2}\) to form sulfur tetrafluoride monoxide (OSF_4) according to the following unbalanced reaction: $$ \mathrm{SF}_{4}(g)+\mathrm{O}_{2}(g) \longrightarrow \operatorname{OSF}_{4}(g) $$ The \(O\) atom and the four \(\mathrm{F}\) atoms in \(\mathrm{OSF}_{4}\) are bonded to a central S atom. (a) Balance the equation. (b) Write a Lewis structure of \(\mathrm{OSF}_{4}\) in which the formal charges of all atoms are zero. (c) Use average bond enthalpies (Table 8.3) to estimate the enthalpy of the reaction. Is it endothermic or exothermic? (d) Determine the electron-domain geometry of OSF \(_{4}\), 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.

Step by step solution

01

Identify the given chemical reaction

We have the given unbalanced chemical reaction: \(SF_4(g) + O_2(g) \longrightarrow OSF_4(g)\)

02

Balance the chemical equation

First, balance the sulfur (S) atoms: \(SF_4(g) + O_2(g) \longrightarrow OSF_4(g)\) There is one S atom on both sides, so it's balanced. Now, balance the oxygen (O) atoms: \(SF_4(g) + 0.5O_2(g) \longrightarrow OSF_4(g)\) Finally, balance the fluorine (F) atoms: \(SF_4(g) + 0.5O_2(g) \longrightarrow OSF_4(g)\) There are 4 F atoms on both sides, so it's balanced. The balanced equation is: \(SF_4(g) + 0.5O_2(g) \longrightarrow OSF_4(g)\) #b. Writing the Lewis Structure of OSF4#

03

Determine the total number of valence electrons

For OSF4: Sulfur (S) has 6 valence electrons Oxygen (O) has 6 valence electrons Each fluorine (F) has 7 valence electrons, so 4 F atoms have 4 * 7 = 28 valence electrons Total valence electrons = 6 + 6 + 28 = 40

04

Place the least electronegative atom at the center

Sulfur is the least electronegative atom in OSF4, so it will be the central atom.

05

Distribute the valence electrons to the outer atoms

There are 4 F atoms and 1 O atom surrounding the S atom. Each F and O atom needs 2 electrons to form a single covalent bond. 2 bonds to F atoms = 2 * 4 F atoms = 8 electrons 1 bond to the O atom = 2 electrons The total number of electrons used for these bonds = 8 + 2 = 10 Remaining valence electrons = 40 - 10 = 30

06

Distribute the remaining valence electrons

Since oxygen has a larger electron affinity than fluorine, we should place the remaining valence electrons on oxygen. Oxygen needs 4 more electrons to fulfill the octet rule. We have 30 remaining electrons to distribute among the four F atoms and O atom: (6 * 4 = 24 electrons) on 4 F atoms, and (6 = 6 electrons) on O atom. Now, the Lewis structure has zero formal charges on all atoms. #c. Enthalpy of the Reaction#

07

Determine the enthalpy of the reaction

Using Table 8.3, we have the following average bond enthalpies: SF(single bond) = 327 kJ/mol O=O (double bond) = 498 kJ/mol S=O (double bond) = 532 kJ/mol F-F (single bond) = 154 kJ/mol Calculate the enthalpy change: Enthalpy change = (Σ Bond enthalpies of products) - (Σ Bond enthalpies of reactants) = (1 * S=O + 4 * SF) - (4 * SF + 0.5 * O=O) Enthalpy change = (1 * 532 + 4 * 327) - (4 * 327 + 0.5 * 498) = 1940 - 1899 = 41 kJ/mol

08

Determine if the reaction is endothermic or exothermic

The enthalpy change is positive (41 kJ/mol), so the reaction is endothermic. #d. Electron-Domain Geometry and Molecular Geometries of OSF4#

09

Determine the electron-domain geometry

The central sulfur (S) atom in OSF4 is surrounded by 4 single bonds and 1 double bond (to oxygen). It has no lone pairs. In total, there are 5 electron domains (3 single bonds, 1 double bond, and 1 lone pair). The electron-domain geometry is trigonal bipyramidal.

10

Two possible molecular geometries

In trigonal bipyramidal electron-domain geometry, there are two possible molecular geometries: 1. Seesaw: when the oxygen occupies an equatorial position 2. T-shaped: when the oxygen occupies an axial position #e. Equatorial and Axial Fluorines in Each Molecular Geometry#

11

Seesaw Geometry

Seesaw Geometry: 3 equatorial fluorines and 1 axial fluorine

12

T-shaped Geometry

T-shaped Geometry: 2 equatorial fluorines and 2 axial fluorines

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