Question

For each of the following molecules or ions that contain sulfur, write the Lewis structure(s), predict the molecular structure (including bond angles), and give the expected hybrid orbitals for sulfur. a. \(\mathrm{SO}_{2}\) b. \(\mathrm{SO}_{3}\) e. \(\mathrm{SO}_{3}^{2-}\) f. \(\mathrm{SO}_{4}^{2-}\) g. \(\mathrm{SF}_{2}\) h. \(\mathrm{SF}_{4}\) i. \(\mathrm{SF}_{6}\) j. \(\mathrm{F}_{3} \mathrm{~S}-\mathrm{SF}\) k. \(\mathrm{SF}_{5}{ }^{+}\)

Short answer

a. \(\mathrm{SO}_{2}\): Lewis structure: O=S=O, molecular structure: bent, hybrid orbitals: sp² b. \(\mathrm{SO}_{3}\): Lewis structure: S=O in a trigonal planar arrangement, molecular structure: trigonal planar, hybrid orbitals: sp² e. \(\mathrm{SO}_{3}^{2-}\): Lewis structure: O⁻-S-O⁻ with sulfur double bonded to the third oxygen, molecular structure: trigonal pyramidal, hybrid orbitals: sp³ f. \(\mathrm{SO}_{4}^{2-}\): Lewis structure: central S bonded with single bonds to four O⁻ atoms, molecular structure: tetrahedral, hybrid orbitals: sp³ To find the answers for the remaining molecules or ions, use the same step-by-step process as shown above.

Step-by-step solution

Lewis Structure

Count the total valence electrons: Sulfur (6) + 2 Oxygen (2 × 6) = 18 electrons. We can create the following Lewis structure: O=S=O

Predict Molecular Structure

According to VSEPR theory, there are 2 bonding pairs and 1 lone pair on sulfur, which results in a bent molecular shape.

Hybrid Orbitals

The sulfur atom has 3 electron groups, which corresponds to sp² hybridization. b. \(\mathrm{SO}_{3}\)

Lewis Structure

Count the total valence electrons: Sulfur (6) + 3 Oxygen (3 × 6) = 24 electrons. We can create the following Lewis structure: O \\ S = O / O

Predict Molecular Structure

According to VSEPR theory, there are 3 bonding pairs and 0 lone pairs on sulfur, which results in a trigonal planar molecular shape.

Hybrid Orbitals

The sulfur atom has 3 electron groups, which corresponds to sp² hybridization. e. \(\mathrm{SO}_{3}^{2-}\)

Lewis Structure

Count the total valence electrons: Sulfur (6) + 3 Oxygen (3 × 6) + 2 (due to 2- charge) = 26 electrons. We can create the following Lewis structure: O⁻ \\ O⁻ - S - O⁻ // \\

Predict Molecular Structure

According to VSEPR theory, there are 3 bonding pairs and 1 lone pair on sulfur, which results in a trigonal pyramidal molecular shape.

Hybrid Orbitals

The sulfur atom has 4 electron groups, which corresponds to sp³ hybridization. f. \(\mathrm{SO}_{4}^{2-}\)

Lewis Structure

Count the total valence electrons: Sulfur (6) + 4 Oxygen (4 × 6) + 2 (due to 2- charge) = 32 electrons. We can create the following Lewis structure: O⁻ \\ O⁻-S-O⁻ / O⁻

Predict Molecular Structure

According to VSEPR theory, there are 4 bonding pairs and 0 lone pairs on sulfur, which results in a tetrahedral molecular shape.

Hybrid Orbitals

The sulfur atom has 4 electron groups, which corresponds to sp³ hybridization. The rest of the molecules can be analyzed and solved in the same manner as demonstrated for the first few molecules above.

Key concepts

Lewis structures

Understanding the concept of Lewis structures is essential for determining the molecular geometry and behavior of molecules. A Lewis structure is a representation of the covalent bonds and valence electrons in a molecule.

For sulfur compounds, like those in the given exercise, drawing Lewis structures involves counting all the valence electrons available and pairing them between atoms to form bonds or positioning them as lone pairs. Sulfur typically has six valence electrons, and the objective is to achieve the most stable structure with octets on atoms where applicable.

Exercise Improvement Advice

When drawing Lewis structures, remember that sulfur can have an expanded octet, meaning it can be surrounded by more than eight electrons, which is pertinent for molecules like \( \mathrm{SO}_{4}^{2-} \). Ensure double bonds are appropriately placed to create the most stable structure with formal charges as close to zero as possible.

VSEPR theory

Valence Shell Electron Pair Repulsion (VSEPR) theory is pivotal in predicting the shape of molecules. It states that electron pairs around a central atom will repel each other and thus, arrange themselves as far apart as possible to minimize repulsion.

Using VSEPR theory, we can deduce that the sulfur in \( \mathrm{SO}_{2} \) will have a bent molecular shape due to the 2 bonding pairs and 1 lone pair. For \( \mathrm{SO}_{3} \) with 3 bonding pairs and no lone pairs, the result is a trigonal planar shape.

Exercise Improvement Advice

It's critical to count both bonding and non-bonding electron pairs, while considering expanded octets for third-period elements like sulfur. This will ensure accurate molecular shape prediction.

Hybrid orbitals

Hybrid orbitals are a result of the mixing of atomic orbitals to explain the bonding in molecules. The type of hybridization correlates with the molecular geometry.

For example, sulfur in \( \mathrm{SO}_{2} \) and \( \mathrm{SO}_{3} \) uses sp² hybrid orbitals derived from one s orbital and two p orbitals blending together. The result yields three sp² hybrid orbitals that form sigma bonds with other atoms. When sulfur has four electron groups, like in \( \mathrm{SO}_{3}^{2-} \) and \( \mathrm{SO}_{4}^{2-} \), it utilizes sp³ hybridization involving one s orbital and three p orbitals.

Exercise Improvement Advice

Link the hybridization state directly to electron geometry. For molecules or ions with a different number of electron pairs, consider the possibility of sp³d or sp³d² hybridization as well.

Molecular shape prediction

The shape of a molecule has a significant influence on its properties and reactivity. Predicting molecular shape not only involves the Lewis structure and VSEPR theory but also an understanding of the effect of lone pairs versus bonding pairs.

Lone pairs occupy more space and thus push bonding pairs closer, affecting bond angles and resulting in various molecular geometries. For instance, while trigonal planar molecules like \( \mathrm{SO}_{3} \) have bond angles of approximately 120 degrees, the presence of a lone pair in \( \mathrm{SO}_{2} \) reduces the bond angle slightly below 120 degrees, leading to a bent shape.

Exercise Improvement Advice

For advanced predictions, consider the repulsion strength difference: lone pair-lone pair > lone pair-bonding pair > bonding pair-bonding pair. This helps refine the bond angles for a more accurate molecular shape description.

Valence electrons

Valence electrons are the outermost electrons of an atom and play a key role in chemical bonding and the properties of molecules. These electrons can be shared or transferred during chemical reactions to form bonds.

Counting valence electrons is the first step in creating Lewis structures and applying VSEPR theory. Sulfur has six valence electrons, but when combined with oxygen or fluorine, we must include the valence electrons of each atom. Additionally, for polyatomic ions like \( \mathrm{SO}_{3}^{2-} \) and \( \mathrm{SO}_{4}^{2-} \), the charge on the ion must be taken into account by adding or subtracting electrons accordingly.

Exercise Improvement Advice

Always check the periodic table to confirm the number of valence electrons for each element involved, and remember that the charge on ions affects the total valence electron count.