Problem 93 - Chemistry Matter and Change

Question

How are the chemical bonds in \(\mathrm{H}_{2}, \mathrm{O}_{2},\) and \(\mathrm{N}_{2}\) different? (Chapter 8\()\)

Step-by-Step Solution

Answer

The chemical bonds in H₂, O₂, and N₂ differ in terms of bond strength, bond order, and electron orbitals involved. H₂ has a bond order of 1 and a single σ bond formed by overlapping 1s orbitals. O₂ has a bond order of 2 and a double bond consisting of one σ bond and one π bond formed by overlapping 2p orbitals. N₂ has a bond order of 3 and a triple bond composed of one σ bond and two π bonds formed by overlapping 2p orbitals. Overall, the bond strength increases in the order H₂ < O₂ < N₂.

Step 1: Identify the type of bonds in each molecule

The molecules H₂, O₂, and N₂ are all diatomic molecules, which means they are made up of two atoms of the same element. The chemical bonds in these molecules are covalent because the atoms share electrons to satisfy the octet rule. Each atom should have 8 electrons in its outermost shell (except in the case of H₂ where it is 2 electrons, following the duet rule).

Step 2: Describe the bond strengths

The bond strength in a molecule is determined by the number of electron pairs shared between the atoms. More electron pairs shared result in a stronger bond. In H₂, there is one bond between the two hydrogen atoms, in O₂ there are two bonds (a double bond), and in N₂ there are three bonds (a triple bond). Therefore, the bond strength increases as H₂ < O₂ < N₂.

Step 3: Determine the bond order

Bond order is calculated as the number of bonds between two atoms divided by the number of atoms. In the case of these diatomic molecules: 1. H₂: bond order is 1 (one bond between two atoms) 2. O₂: bond order is 2 (double bond between two atoms) 3. N₂: bond order is 3 (triple bond between two atoms) The bond order provides information about the bond strength, with higher bond orders corresponding to stronger bonds.

Step 4: Discuss the electron orbitals involved

The chemical bonds in these diatomic molecules are formed by overlapping orbitals on the individual atoms, which allows them to share electrons. 1. H₂: The two hydrogen atoms each have one electron in their 1s orbitals. These orbitals overlap, forming a single σ bond. 2. O₂: The oxygen atoms each have two half-filled 2p orbitals. These orbitals overlap end-on to form a single σ bond and side-by-side to form a single π bond, creating a double bond in total. 3. N₂: The nitrogen atoms each have three half-filled 2p orbitals. They overlap end-on to form a single σ bond and side-by-side to form two π bonds, creating a triple bond in total. In summary, the chemical bonds in H₂, O₂, and N₂ are different in terms of bond strength, bond order, and the makeup of the electron orbitals involved. The bond strength and bond order increase as H₂ < O₂ < N₂ and the number and type of orbitals involved in bond formation also varies between the molecules.

Key Concepts

Bond Strength

Bond strength refers to the energy required to break a bond between two atoms. The strength of a covalent bond depends on the number of electron pairs shared by the atoms.
More shared pairs mean stronger bonds. This is because more force is required to break the attraction between the atoms as more electrons are involved.

In the molecules

• **H₂**: One pair of electrons is shared, so it has a single bond. This is the weakest bond among the three as fewer electrons contribute to the bonding interaction.
• **O₂**: Two electron pairs are shared, resulting in a double bond. This makes the bond stronger than in H₂.
• **N₂**: Three electron pairs are shared, forming a triple bond. This bond is the strongest because it has the highest number of shared electrons.

Bond strength increases in the order: H₂ < O₂ < N₂. Stronger bonds are generally shorter and have higher bond dissociation energies.

Bond Order

Bond order represents the number of chemical bonds between a pair of atoms. It provides insight into the stability of a molecule. A higher bond order indicates stronger and more stable bonds.

For the diatomic molecules:

• **H₂**: Has a bond order of 1, corresponding to its single bond. It's stable but weaker compared to its counterparts.
• **O₂**: Has a bond order of 2, due to its double bond. This makes it stronger than H₂ but not as strong as N₂.
• **N₂**: With a bond order of 3, due to its triple bond, it is the most stable and strongly bonded among the three molecules.

The bond order directly correlates with bond strength, so a greater bond order means more attraction between atoms, leading to stronger bonds.

Electron Orbitals

Chemical bonds are formed through the interaction and overlap of electron orbitals. These orbitals are regions around an atom where electrons are likely to be found and play a crucial part in bond formation.
Understanding orbitals gives us insight into the geometry and type of bonds created.

In the molecules:

• **H₂**: Two 1s orbitals from each hydrogen atom overlap to form a single σ bond.
• **O₂**: The oxygen atoms overlap two of their 2p orbitals. One pair overlaps endwise to form a σ bond, and another overlaps sideways to create a π bond. This results in a double bond configuration with both σ and π bonds.
• **N₂**: Nitrogen atoms have three 2p orbitals that form bonds. One pair overlaps endwise for a σ bond, and two pairs overlap sideways for π bonds, forming a triple bond. This complex arrangement accounts for the molecule's exceptional bond strength.

Orbitals provide a visual way to understand how electrons form bonds and why the molecules behave as they do. Different orbital overlaps result in varied bond types and strengths, explaining the unique characteristics of each molecule.