Question

The transport of \(\mathrm{O}_{2}\) in the blood is carried out by hemoglobin. Carbon monoxide can interfere with oxygen transport because hemoglobin has a stronger affinity for CO than for \(\mathrm{O}_{2}\). If \(\mathrm{CO}\) is present, normal uptake of \(\mathrm{O}_{2}\) is prevented, depriving the body of needed oxygen. Using the molecular orbital model, write the electron configurations for CO and for \(\mathbf{O}_{2} .\) From your configurations, give two property differences between CO and \(\mathbf{O}_{2}\)

Short answer

The electron configurations for CO and O2 are, respectively, \(1\sigma_{g}^{2}\) \(1\sigma_{u}^{*2}\) \(2\sigma_{g}^{2}\) \(2\sigma_{u}^{*2}\) \(3\sigma_{g}^{2}\) \(1\pi_{u}^{3}\) and \(1\sigma_{g}^{2}\) \(1\sigma_{u}^{*2}\) \(2\sigma_{g}^{2}\) \(2\sigma_{u}^{*2}\) \(3\sigma_{g}^{2}\) \(1\pi_{u}^{4}\). The two property differences based on these configurations are: 1) Bond order: O2 is more stable with a double bond and a bond order of 2, while CO has a bond order of 1.5. 2) Magnetic properties: Both CO and O2 are paramagnetic, but O2 has a higher magnetic moment due to having two unpaired electrons in the \(1\pi_{u}\) orbital, while CO has only one unpaired electron.

Step-by-step solution

Understand the Molecular Orbital Theory

In the molecular orbital theory, atomic orbitals combine to form molecular orbitals, which are spread out over the entire molecule. The bonding molecular orbitals are formed by mixing of atomic orbitals of two atoms, which are lower in energy, while anti-bonding molecular orbitals are higher in energy. Electrons in bonding orbitals stabilize a molecule, while those in anti-bonding orbitals make the molecule less stable.

Determine the Electron Configurations for CO and O2

To determine the electron configurations for CO and O2, we first need to determine the molecular orbitals for each. For diatomic molecules like CO and O2, we use the following order of atomic orbitals: \(1\sigma_{g}\), \(1\sigma_{u}^{*}\), \(2\sigma_{g}\), \(2\sigma_{u}^{*}\), \(3\sigma_{g}\), \(1\pi_{u}\), \(1\pi_{u}^{*}\), \(3\sigma_{u}^{*}\). First, count the total number of electrons in each molecule: - For CO: 6 electrons from oxygen and 7 electrons from carbon, 13 electrons total. - For O2: 8 electrons from each oxygen, 16 electrons total. Now, let's populate the molecular orbitals with the electrons following Hund's rule and Pauli exclusion principle: - CO electron configuration: \(1\sigma_{g}^{2}\) \(1\sigma_{u}^{*2}\) \(2\sigma_{g}^{2}\) \(2\sigma_{u}^{*2}\) \(3\sigma_{g}^{2}\) \(1\pi_{u}^{3}\) - O2 electron configuration: \(1\sigma_{g}^{2}\) \(1\sigma_{u}^{*2}\) \(2\sigma_{g}^{2}\) \(2\sigma_{u}^{*2}\) \(3\sigma_{g}^{2}\) \(1\pi_{u}^{4}\)

Identify the Property Differences

Based on the electron configurations of CO and O2, let's analyze the differences in properties: 1. Bond order: Bond order determines the stability of a molecule. The bond order is calculated as \(\frac{1}{2}\) (number of bonding electrons - number of anti-bonding electrons). From the electron configurations: - CO bond order: \(\frac{1}{2}\)(8-5) = 1.5 - O2 bond order: \(\frac{1}{2}\)(10-6) = 2 Thus, O2 has a double bond, making it more stable compared to CO, which has a bond order of 1.5. 2. Magnetic properties: The presence of unpaired electrons in a molecule determines its magnetic properties. Molecules with unpaired electrons are paramagnetic, while those with no unpaired electrons are diamagnetic. - CO has one unpaired electron in the \(1\pi_{u}\) orbital, making it paramagnetic. - O2 has two unpaired electrons in the \(1\pi_{u}\) orbital, making it paramagnetic but with a higher magnetic moment compared to CO. In conclusion, CO and O2 differ in their bond order and magnetic properties due to their respective electron configurations.

Key concepts

Electron Configuration

Electron configuration refers to the way electrons are arranged in an atom or molecule. Understanding these configurations helps elucidate many chemical properties, like bonding and magnetism. In molecular orbital theory, atomic orbitals combine to form molecular orbitals, which extend over the entire molecule. For diatomic molecules like CO and O₂, we use specific molecular orbital order to assign their electron configurations.

For CO (Carbon Monoxide), it consists of 13 electrons: 6 from oxygen and 7 from carbon. Using the molecular orbital order: 1σg, 1σu*, 2σg, 2σu*, 3σg, 1πu, 1πu*, 3σu*, CO's electronic configuration is:

• 1σg²
• 1σu*²
• 2σg²
• 2σu*²
• 3σg²
• 1πu³

For O₂ (Oxygen), which has 16 electrons (8 from each oxygen atom), the configuration follows the same order:

• 1σg²
• 1σu*²
• 2σg²
• 2σu*²
• 3σg²
• 1πu⁴

Bond Order

Bond order is a concept used in molecular orbital theory to determine the strength and stability of bonds within a molecule. It is defined as half the difference between the number of bonding electrons (which help hold the atoms together) and anti-bonding electrons (which work against the bond formation).

The formula for bond order is:\[\text{Bond order} = \frac{1}{2} (\text{number of bonding electrons} - \text{number of antibonding electrons})\]For CO, with its electron configuration, you find

• Bonding electrons = 8
• Antibonding electrons = 5

Resulting in a bond order of \[\frac{1}{2} (8 - 5) = 1.5\]For O₂, the presence of 10 bonding and 6 antibonding electrons translates into a bond order of:\[\frac{1}{2} (10 - 6) = 2\]This suggests that O₂, with its double bond, is more stable than CO, having a bond order of 1.5.

Magnetic Properties

Magnetic properties of molecules depend on the presence of unpaired electrons. In a molecule, electrons in molecular orbitals can either be paired or unpaired. A molecule with unpaired electrons is termed paramagnetic, and one with no unpaired electrons is called diamagnetic.

Using this, for CO, which has one unpaired electron in the 1πu orbital, it behaves as a paramagnetic substance. This means it will be attracted to a magnetic field but weakly because there's only one unpaired electron.

In contrast, O₂ has two unpaired electrons in the 1πu orbital. This contributes to its paramagnetic nature but with a more substantial magnetic effect compared to CO, due to the additional unpaired electron enhancing its interaction with magnetic fields.

Hemoglobin

Hemoglobin is a complex protein found in red blood cells responsible for transporting oxygen throughout the body. Its ability to bind oxygen stems from its quaternary structure, which includes four subunits, each with an iron atom that can bind one O₂ molecule. This makes hemoglobin crucial for oxygen delivery to tissues in mammals.

However, hemoglobin's binding capabilities can be compromised. For example, carbon monoxide (CO) has a much higher affinity for hemoglobin than oxygen (O₂). This can disrupt normal oxygen transport since CO effectively "locks" hemoglobin in a state that prevents the uptake and further release of oxygen. This is why CO poisoning is dangerous—even small concentrations can hinder oxygen transport dramatically.

Oxygen Transport

Oxygen transport is a vital process that supports cellular respiration in animals. Hemoglobin plays a crucial role as it picks up oxygen in the lungs and releases it where it's needed in the body.

This transport is facilitated by the reversible binding of oxygen to hemoglobin. Each hemoglobin molecule can carry up to four oxygen molecules, increasing efficiency in oxygen transport. The high affinity of hemoglobin for oxygen at high concentrations (like in the lungs) and its decreased affinity at lower concentrations (like in tissues) allows for effective oxygen release.

Disruptions in this process, such as those caused by CO, can be life-threatening. When CO binds to hemoglobin with greater affinity than O₂, it distorts the normal functioning by preventing oxygen from binding, leading to oxygen deprivation in tissues and organs. Thus, understanding these mechanisms is critical in biochemistry and medicine.