Problem 126 - Chemistry Principles and Practice

Question

Recently, the compound \(\mathrm{CF}_{3} \mathrm{SF}_{5}\) was discovered in the atmosphere and identified as a potential greenhouse gas. Assume the carbon and sulfur atoms are both central atoms, and draw the Lewis structure for this compound. What is the hybridization of each central atom and the bond angles with the surrounding atoms?

Step-by-Step Solution

Answer

Carbon has sp3 hybridization with ~109.5° bond angles; sulfur has sp3d2 with ~90° and ~120° bond angles.

Step 1: Identify the Atoms and Bonds

The compound is CF3SF5. Here, "C" represents carbon, "S" represents sulfur, "F" represents fluorine, and the subscripts denote the number of each type of atom bonded to them. Carbon and sulfur are the central atoms.

Step 2: Determine Valence Electrons

Carbon has 4 valence electrons, fluorine has 7 valence electrons, and sulfur has 6 valence electrons. The total valence electrons for CF3SF5 are calculated as: Carbon = 4, Sulfur = 6, Fluorine (8 F atoms total due to subscript) = 8*7 = 56. Total valence electrons = 4 + 6 + 56 = 66.

Step 3: Draw Lewis Structure

Start by placing carbon and sulfur as the central atoms. Bond carbon to three fluorines and sulfur to five fluorines. Connect carbon and sulfur with a single bond. Distribute remaining valence electrons to fulfill the octet rule for all atoms involved. CF3 is attached to carbon and SF5 is attached to sulfur.

Step 4: Determine Hybridization of Carbon

Carbon is bonded to three fluorines and one sulfur, making a total of four sigma bonds. Therefore, the hybridization of carbon is sp3.

Step 5: Determine Hybridization of Sulfur

Sulfur is bonded to five fluorines and one carbon atom, a total of six sigma bonds/lone pairs. Sulfur has sp3d2 hybridization owing to its six bonded groups.

Step 6: Calculate Bond Angles

With carbon's sp3 hybridization, the expected bond angles around carbon are approximately 109.5°. For sulfur's sp3d2 hybridization, the bond angles are approximately 90° and 120°.

Key Concepts

Hybridization

In chemistry, hybridization is a concept that helps us understand the sharing and overlapping of orbitals by different atoms to form molecules. In the case of our compound \( \text{CF}_3\text{SF}_5 \), we have two central atoms: carbon and sulfur. Their hybridization is critical to determining the molecule's shape and bond angles.

**Carbon's Hybridization:**

• Carbon is bonded to three fluorine atoms and one sulfur atom.
• This setup involves a total of four sigma bonds.
• For carbon to form these bonds, its orbitals undergo \( sp^3 \) hybridization.

The \( sp^3 \) hybridization means one s orbital mixes with three p orbitals, resulting in four equivalent orbitals pointing in different directions.

**Sulfur's Hybridization:**

• Sulfur is bonded to five fluorine atoms and one carbon atom.
• This configuration involves six bonding interactions.
• Therefore, sulfur undergoes \( sp^3d^2 \) hybridization.

This results in six hybrid orbitals arranged in an octahedral geometry, which helps explain the shape of the portion of the molecule around sulfur.

Bond Angles

Bond angles are the angles between adjacent lines representing bonds connecting atoms. The bond angles greatly depend on the hybridization of the central atoms.

**Carbon's Bond Angles:**

• With \( sp^3 \) hybridization, carbon’s bond angles are close to \( 109.5^{\circ} \).
• This tetrahedral angle minimizes electron pair repulsions around the carbon atom.

For example, in \( \text{CF}_3 \), each F-C-F angle is roughly \( 109.5^{\circ} \).

**Sulfur's Bond Angles:**

• The \( sp^3d^2 \) hybridization results in two distinct sets of bond angles.
• One set of bond angles measures approximately \( 90^{\circ} \), characteristic of octahedral structures.
• Another set measures around \( 120^{\circ} \), indicative of trigonal bipyramidal geometries present within the molecule.

These angles are vital for understanding how the electronic distribution around sulfur affects molecular geometries, as in \( \text{SF}_5 \).

Greenhouse Gas

Greenhouse gases are molecules in the atmosphere that can absorb infrared radiation and trap heat, contributing to the greenhouse effect. \( \text{CF}_3\text{SF}_5 \) has been identified as an emerging greenhouse gas.

**Why It Matters:**

• These gases play a crucial role in global temperature regulation by trapping heat.
• However, excessive concentrations can lead to global warming.

**Characteristics of \( \text{CF}_3\text{SF}_5 \):**

• It has multiple polar bonds due to the high electronegativity difference between fluorine and the central carbon and sulfur.
• This makes the molecule effective at absorbing and emitting infrared radiation.
• Its stability in the atmosphere could lead to long-term effects on earth’s climate.

Understanding and monitoring such gases are essential for climate change mitigation strategies.

Valence Electrons

Valence electrons are the outermost electrons of an atom and play a significant role in chemical bonding and reactions. For \( \text{CF}_3\text{SF}_5 \), knowing the number of valence electrons helps us draw the Lewis structure.

**Breaking It Down:**

• **Carbon** has 4 valence electrons.
• **Sulfur** has 6 valence electrons.
• **Fluorine** has 7 valence electrons, and given there are 8 fluorine atoms, the total contribution from fluorine is \( 8 \times 7 = 56 \) electrons.

**Total Valence Electrons:**

• Adding these, the molecule has a total of \( 66 \) valence electrons.
• These electrons used to form bonds and fulfill the octet rule around each atom.

Valence electrons are essential for predicting molecular structures and ensuring that each atom achieves a stable electronic arrangement in the structure.