Problem 58 - Chemistry The Central Science In Si Units

Question

The oxygen atoms in \(\mathrm{O}_{2}\) participate in multiple bonding, whereas those in hydrogen peroxide, \(\mathrm{H}_{2} \mathrm{O}_{2},\) do not. (a) Draw Lewis structures for both molecules. (b) What is the hybridization of the oxygen atoms in each molecule? (c) Which molecule has the stronger \(\mathrm{O}-\mathrm{O}\) bond?

Step-by-Step Solution

Answer

(a) O2 has a double bond, H2O2 has single bonds. (b) O2: sp², H2O2: sp³. (c) O2 has the stronger O-O bond.

Step 1: Understanding Lewis Structures

Lewis structures, also known as Lewis dot structures, help visualize the bonding in molecules. Valence electrons are represented by dots around the elements. For \(\mathrm{O}_2\), each oxygen atom shares two pairs of electrons, forming a double bond. The Lewis structure for \(\mathrm{O}_2\) shows a double bond between two oxygen atoms, each with two lone pairs of electrons.**Lewis Structure of \(\mathrm{O}_2\):**\[ \text{O}=\text{O} \]For \(\mathrm{H}_2\mathrm{O}_2\), each oxygen forms a single bond with one hydrogen and one single bond with another oxygen, resulting in a structure with single bonds.**Lewis Structure of \(\mathrm{H}_2\mathrm{O}_2\):**\[ \text{H}-\text{O}-\text{O}-\text{H} \]Each oxygen in \(\mathrm{H}_2\mathrm{O}_2\) has two lone pairs.

Step 2: Determining the Hybridization of Oxygen Atoms

Hybridization involves mixing atomic orbitals to form new hybrid orbitals suitable for the pairing of electrons to form bonds. In \(\mathrm{O}_2\), the oxygen atoms form a double bond, using sp\(^2\) hybrid orbitals since one \(\text{p}\) orbital remains unhybridized.In \(\mathrm{H}_2\mathrm{O}_2\), each oxygen atom forms two single bonds, requiring sp\(^3\) hybridization, which accounts for four hybrid orbitals (two for bonds and two for lone pairs).

Step 3: Comparing O-O Bond Strength

The bond strength between two atoms is generally related to the bond order; higher bond order corresponds to stronger bonds. In \(\mathrm{O}_2\), the oxygen-oxygen bond is a double bond, having a bond order of 2. In \(\mathrm{H}_2\mathrm{O}_2\), the bond is a single bond with a bond order of 1. Therefore, the double bond in \(\mathrm{O}_2\) is stronger than the single bond in \(\mathrm{H}_2\mathrm{O}_2\).

Key Concepts

Hybridization of Oxygen

In the molecular world, hybridization is a process where atomic orbitals mix to create new orbitals suitable for bonding. This is crucial for understanding how oxygen bonds in different molecules. Let's take a closer look at the hybridization of oxygen in both O₂ and H₂O₂.

For O₂:

• O₂ features a double bond between the oxygen atoms.
• To account for this double-bond, oxygen atoms utilize sp² hybridization. This occurs because one p orbital remains unhybridized and is involved in forming the second (complementary to the first sigma) pi-bond.

For H₂O₂:

• Each oxygen atom only makes single bonds, necessitating sp³ hybridization.
• In this case, all p orbitals are used to form four sp³ hybrid orbitals, two for bonding and two accommodating the lone pairs.

Understanding the distinction between these hybridizations is essential for appreciating the different bonding capabilities of oxygen atoms in these molecules.

Multiple and Single Bonds

The differences in bonding between multiple and single bonds is a key principle in chemistry, affecting molecular structure and stability.

**Multiple Bonds in O₂:**

• In O₂, a double bond is formed between the oxygen molecules.
• A double bond consists of one sigma bond and one pi bond. This leads to a more rigid structure and increased bond strength.
• The presence of the pi bond is crucial for understanding why O₂ has a higher bond energy and shorter bond length.

**Single Bonds in H₂O₂:**

• In contrast, H₂O₂ has only single bonds between its oxygen atoms and hydrogen atoms.
• Single bonds involve just a sigma bond.
• These bonds offer greater freedom for rotation about the bond axis compared to double bonds, but they are less stable and weaker.

The hybridization and bonding differences explain why the molecules have different properties.

Bond Order and Bond Strength

Bond order plays a significant role in determining bond strength and stability. It is essentially a measure of the number of chemical bonds between a pair of atoms.

**Bond Order in O₂:**

• In O₂, the bond order is 2 because it has a double bond.
• This higher bond order indicates a stronger bond compared to single bonds.

**Bond Order in H₂O₂:**

• Conversely, in H₂O₂, the bond order is 1, indicating a single bond.
• With a lower bond order, the bond is weaker and generally longer.

The strength of bonds directly correlates to bond order; therefore, a higher bond order typically means a stronger and shorter bond. Understanding these concepts helps predict the physical and chemical properties of molecules.