Problem 53 - Chemistry and Chemical Reactivity

Question

Consider the carbon-oxygen bond in formaldehyde \(\left(\mathrm{CH}_{2} \mathrm{O}\right)\) and carbon monoxide (CO). In which molecule is the CO bond shorter? In which molecule is the CO bond stronger?

Step-by-Step Solution

Answer

CO bond is shorter and stronger in carbon monoxide (CO).

Step 1: Identify Bond Types

In formaldehyde ( \(\mathrm{CH}_{2}\mathrm{O})\), the carbon-oxygen bond involves a double bond. In carbon monoxide (CO), the carbon-oxygen bond involves a triple bond due to the presence of a coordinate bond along with the usual double bond.

Step 2: Compare Bond Orders

The bond order indicates the number of shared electron pairs between two atoms. For CO, the bond order is 3 (triple bond), while for the carbon-oxygen bond in formaldehyde, it is 2 (double bond).

Step 3: Relate Bond Order to Bond Length

A higher bond order correlates to shorter bond lengths. Therefore, because the bond order in CO (3) is higher than in formaldehyde (2), the CO bond in carbon monoxide will be shorter.

Step 4: Relate Bond Order to Bond Strength

Higher bond orders also correspond to stronger bonds, as more electron pairs mean a stronger interaction between the atoms. Hence, the bond in CO is stronger than in formaldehyde.

Key Concepts

Bond Order

Bond order is a fundamental concept in understanding chemical bonding. It helps determine how many electron pairs are being shared between two atoms. In simple terms, it's like counting the number of strings holding two pieces of wood together - more strings mean the wood pieces are held more tightly.

• A single bond has a bond order of 1.
• A double bond has a bond order of 2.
• A triple bond has a bond order of 3.

The bond order can be calculated by comparing the number of bonding and anti-bonding electrons. For example, in a molecule of carbon monoxide (CO), there is a triple bond between carbon and oxygen, thus the bond order is 3. On the other hand, formaldehyde ( ext{CH}_2 ext{O} ) has a double bond between carbon and oxygen, with a bond order of 2. Higher bond orders not only mean a greater number of shared electrons, but also imply stronger and typically shorter bonds. This means more stability in molecules with high bond orders.

Bond Length

Bond length is the distance between the nuclei of two bonded atoms. Imagine two magnets being pulled toward each other; the stronger the pull (or bond strength), the closer they get. The relationship between bond order and bond length is inversely proportional. This means:

• Higher bond order (such as in CO) leads to shorter bond lengths.
• Lower bond order (like in formaldehyde) results in longer bond lengths.

For instance, the carbon-oxygen bond in formaldehyde has a double bond, resulting in a bond length longer than that in carbon monoxide, which has a triple bond. Since more electron pairs are shared in a triple bond, the atoms are pulled closer together, decreasing the bond length. It's crucial to remember this relationship because understanding bond length can predict molecule behavior and reactivity in various chemical reactions.

Bond Strength

Bond strength reflects the energy required to break a bond between two atoms. It's like trying to break a stick; the bigger or tougher the stick, the more force you need. A higher bond order signifies stronger bonds, as more electron pairs are shared between atoms, creating a stronger electromagnetic attraction.

• In carbon monoxide (CO), the bond has a bond order of 3, explaining its stronger bond compared to formaldehyde.
• Formaldehyde, with a bond order of 2, has a weaker bond due to fewer shared electrons.

The strength of a bond not only impacts its resistance to breaking but also influences the compound's chemical properties. Stronger bonds generally lead to less reactive molecules, as more energy is required to disrupt their structure. Understanding bond strength is vital for predicting how substances interact and respond to environmental changes, affecting their overall stability.