Problem 55 - Chemistry: The Central Science in SI Units, Global Edition

Question

Compare the \(\mathrm{O}-\mathrm{O}\) bond length in \(\mathrm{O}_{2}\) versus \(\mathrm{H}_{2} \mathrm{O}_{2}\). Which bond is shorter? Why?

Step-by-Step Solution

Answer

The O-O bond length in \(O_2\) is shorter than in \(H_2O_2\) because of the stronger double bond in \(O_2\), which results from a greater number of shared electrons between the oxygen atoms. This stronger bonding leads to a shorter bond length as the oxygen atoms are pulled closer together.

Step 1: Identify the molecular structures for O₂ and H₂O₂

Both O₂ and H₂O₂ contain an O-O bond. Let's first understand the molecular structure for both molecules. \(O_2\) is a diatomic molecule consisting solely of two oxygen atoms bonded together. The O-O bond in O₂ can be represented in Lewis structures as a double bond: O = O \(H_2O_2\) (hydrogen peroxide) is a molecule consisting of two oxygen atoms and two hydrogen atoms. It has the following molecular structure: H - O - O - H It is essential to notice that in this molecule, the O-O bond is a single bond.

Step 2: Understand the electronic configuration and bonding in oxygen atoms

The electronic configuration of each oxygen atom is: 1s² 2s² 2p⁴ This means that each oxygen atom has six valence electrons - two in the 2s orbital and four in the 2p orbitals. In O₂, two oxygen atoms form a double bond, which means they share four electrons between them. This contributes to a stronger and shorter bond. In H₂O₂, the two oxygen atoms are connected via a single bond, sharing only two electrons, which results in a weaker and longer bond.

Step 3: Compare the bond length in O₂ and H₂O₂

Now that we understand the electronic configuration and bonding in oxygen atoms for both molecules, we can conclude which bond is shorter. The O-O double bond in O₂ is stronger than the O-O single bond in H₂O₂ because more electrons are shared between the two oxygen atoms in O₂. Due to this strong connection and the higher number of shared electrons, the double bond in O₂ will be shorter as the atoms are pulled closer together due to stronger electrostatic forces between the oxygen atoms.

Step 4: Conclusion

In conclusion, the O-O bond length in O₂ is shorter than the O-O bond length in H₂O₂ due to the greater number of shared electrons and stronger bonding in the O₂ molecule.

Key Concepts

Oxygen Molecules

Oxygen molecules are an important topic in chemistry, and they are represented by the chemical formula \( O_2 \). These molecules are the primary form of oxygen in our atmosphere and play a crucial role in many chemical reactions, including combustion and respiration.
An oxygen molecule is diatomic, meaning it is composed of two oxygen atoms. These atoms are linked together by a double bond, represented as \( O = O \). This double bonded structure allows the molecule to be stable and efficiently transportable in various biological and chemical processes.
Oxygen molecules have a bond length of about 121 pm (picometers). This is relatively short due to the double bond, which involves the sharing of four electrons between the atoms, creating a stronger attraction that pulls the atoms closer together. The compact nature of \( O_2 \) contributes to its stability and reactivity, making it a vital molecule in many essential reactions.

Chemical Bonding

Chemical bonding refers to the forces that hold atoms together within a molecule. These bonds are essential for forming all the substances we encounter daily. There are three main types of chemical bonds: ionic, covalent, and metallic.
In the case of oxygen molecules \( O_2 \), the bond is covalent. Covalent bonds are formed by the sharing of electrons between atoms. Specifically, oxygen atoms each have six valence electrons and need two more to achieve a full outer shell, which is why they form a double bond.

• A double bond involves sharing four electrons between two atoms.
• This bond is stronger and shorter compared to a single bond, which shares only two electrons.
• The strength of a double bond arises from the greater electrostatic attraction between the paired atoms, which also results in a shorter bond length.

In contrast, hydrogen peroxide (\( H_2O_2 \)) contains an O-O single bond. This type of bond shares only two electrons, resulting in a weaker and longer bond compared to the double bond in \( O_2 \). Understanding these differences in electron sharing helps in comprehending why different substances have varying bond strengths and lengths.

Molecular Structure

Molecular structure greatly influences the properties and behavior of compounds. It refers to the arrangement of atoms within a molecule and the chemical bonds that connect them. Recognizing these structures is vital for predicting how substances interact and form.
For instance, the molecular structure of \( O_2 \) is straightforward with a linear arrangement. This linearity, coupled with the double bond, enhances its ability to interact efficiently with other compounds during reactions such as combustion and oxidation. The simplicity of its structure also contributes to its low reactivity with certain substances, like inert gases.

• Linear molecules, like \( O_2 \), often exhibit symmetrical electron distribution.
• This symmetry minimizes polar interactions, generally making the molecule non-polar.
• The non-polar nature of \( O_2 \) allows it to dissolve in non-polar solvents effectively.

Comparatively, hydrogen peroxide (\( H_2O_2 \)) has a more complex bent structure due to the presence of additional hydrogen atoms. This bent configuration affects its physical properties, such as boiling and melting points, and its chemical reactivity. The molecular structure not only dictates the bond length but also influences the molecule's interactions and stability in different environments.