Question

Look up the energies for the bonds in \(\mathrm{CO}\) and \(\mathrm{N}_{2}\) . Although the bond in \(\mathrm{CO}\) is stronger, \(\mathrm{CO}\) is considerably more reactive than \(\mathrm{N}_{2}\) . Give a possible explanation.

Short answer

Although CO has a stronger bond energy than N2 (1072 kJ/mol vs. 945 kJ/mol), it is more reactive due to other factors such as the presence of lone pairs on carbon and oxygen atoms and the nature of its molecular orbitals. CO's polar nature and molecular orbitals make it more susceptible to chemical reactions, while N2's symmetrical linear geometry, triple bond, and absence of lone pairs contribute to its stability and low reactivity.

Step-by-step solution

Look up bond energies for CO and N2.

Bond energies can be found in various resources such as textbooks, online databases, or reference tables. According to most sources, the bond energy of CO is approximately 1072 kJ/mol, and the bond energy of N2 is approximately 945 kJ/mol.

Compare bond energies.

Comparing the bond energies of CO (1072 kJ/mol) and N2 (945 kJ/mol), we can see that the bond in CO is stronger than the bond in N2.

Explain the reactivity of CO and N2.

Despite having a stronger bond, CO is more reactive than N2. This is because bond energy is not the only factor that determines the reactivity of a molecule. Other factors, such as the presence of lone pairs on the carbon and oxygen atoms in CO and the molecular orbitals in both molecules, influence their reactivity. In the case of N2, the molecule has a triple bond between the two nitrogen atoms, which contributes to its stability and low reactivity. Moreover, N2 has a symmetrical linear geometry and no lone pairs on the nitrogen atoms. These factors make N2 a relatively unreactive gas. On the other hand, CO has a double bond between the carbon and oxygen atoms, and both atoms have lone pairs, which makes the molecule more polar. The presence of lone pairs on the carbon and oxygen atoms allows for interactions with other molecules, making CO more reactive than N2. A possible explanation for CO's greater reactivity is the presence of molecular orbitals with varying energy levels in CO, making it more susceptible to undergoing chemical reactions. For example, CO can react with iron, forming a strong bond with the metal, whereas N2 is not able to form such strong interactions with metals. In conclusion, although CO has a stronger bond energy than N2, its greater reactivity is due to other factors, including the presence of lone pairs on the carbon and oxygen atoms and the nature of its molecular orbitals that make it more prone to interacting with other molecules.

Key concepts

Reactivity Comparison

Reactivity is the tendency of a substance to engage in chemical reactions, which doesn’t always correlate directly with bond strength. While bond energy does play a role in stability, it’s not the only factor. In our comparison between carbon monoxide (CO) and nitrogen ( 2), we find that despite CO having a stronger bond energy (1072 kJ/mol versus N2’s 945 kJ/mol), it is more reactive. This highlights that other chemical properties, such as molecular structure and electron distribution, can have a significant impact on how a molecule behaves in reactions.

In CO, the presence of lone pairs on carbon and oxygen atoms increases the molecule's potential interactions. This is a feature that N2 lacks due to its stable triple bond and linear, non-polar structure. When considering reactivity, it's crucial to recognize that properties like lone pairs, molecular polarity, and the specific environments molecules interact with can heavily influence how and when reactions occur.

Molecular Orbitals

Understanding molecular orbitals helps explain why CO is more reactive than N2 despite its stronger bond. Molecular orbitals are regions in a molecule where electrons are likely to be found, impacting chemical bonding and reactivity. In CO, the interaction of these orbitals can create areas of electron density that make the molecule more reactive.

Molecular orbitals in CO involve a mix of \(\sigma\)and\(\pi\)bonding, along with non-bonding orbitals due to lone pairs. These orbitals allow CO to interact with various elements and factors in its environment. For example, CO can adsorb onto metal surfaces because its molecular orbitals can overlap with the orbitals of metals, forming coordinate covalent bonds. This is not typically seen with N2 because its electrons are tightly held in a more stable configuration.
Furthermore, because of the availability of higher energy molecular orbitals in CO, it is more susceptible to participating in both donation and acceptance of electrons, increasing its range of reactivity compared to N2.

Lone Pairs Effect

Lone pairs play a significant role in the chemical reactivity of molecules like CO. These are pairs of valence electrons that are not shared with another atom and remain outside of bonding interactions. In CO, lone pairs exist on both carbon and oxygen, influencing its chemical behavior.

These lone pairs make CO a polar molecule, with distinct regions of partial negative and positive charges. This polarity allows CO to form hydrogen bonds or dipole interactions with other molecules more easily than non-polar N2. The presence of lone pairs also provides CO with active sites for chemical reactions. These electron-rich areas can readily engage in chemical interactions, such as bonding with metals in industrial processes.
In contrast, N2 lacks lone pairs on nitrogen atoms in its stable triple-bonded form, limiting its reactivity. This illustrates how lone pairs can significantly alter a molecule's ability to interact and react with other substances.