Problem 85 - Chemistry Matter and Change

Question

In the molecules \(\mathrm{CO}, \mathrm{CO}_{2},\) and \(\mathrm{CH}_{2} \mathrm{O},\) which \(\mathrm{C}-\mathrm{O}\) bond is the shortest? Which \(\mathrm{C}-\mathrm{O}\) bond is the strongest?

Step-by-Step Solution

Answer

The C-O bond in CO is the shortest and the strongest.

Step 1: Identify Bond Types

To determine bond length and strength, we need to identify the type of bond present in each molecule. In CO, the bond is a triple bond. In CO₂, the bonds are two double bonds. In CH₂O (formaldehyde), the bond is a double bond.

Step 2: Compare Bond Types

Triple bonds are generally shorter and stronger than double bonds because they have more shared electron pairs, which increases the attractive forces holding the atoms together. Double bonds are shorter and stronger than single bonds but not as short or strong as triple bonds.

Step 3: Identify Shortest Bond

Since triple bonds are shorter than double bonds, the C-O bond in CO is the shortest compared to the C-O bonds in CO₂ and CH₂O, both of which are double bonds.

Step 4: Identify Strongest Bond

The strength of a bond is directly related to the number of shared electrons: more shared electrons mean a stronger bond. Thus, the C-O bond in CO is the strongest because it is a triple bond, while the other C-O bonds are double bonds.

Key Concepts

C-O bond length

Bond length is a crucial concept in understanding chemical bonding, especially when it comes to carbon and oxygen atoms. It's the distance between the nuclei of two bonded atoms. In the molecules CO, CO₂, and CH₂O, the length of the C-O bond can greatly impact the molecule's properties.

Triple bonds, like the one found in CO, are shorter than double bonds. This is due to the multiple pairs of electrons that attract the two nuclei closer together. In both CO₂ and CH₂O, the C-O bonds are double bonds, which are longer compared to the triple bond in CO. Double bonds have more distance between the carbon and oxygen atom due to fewer shared electron pairs.

So, the C-O bond in CO is the shortest, illustrating how the type of bond influences bond length. Shorter bonds usually correlate with stronger bonds, which we'll explore next.

C-O bond strength

Bond strength refers to the energy required to break a bond. It's closely linked to bond length — shorter bonds are generally stronger due to increased electron attraction. In CO, CO₂, and CH₂O, understanding the C-O bond strength helps in evaluating the molecule's stability and reactivity.

The C-O bond strength is the greatest in CO because it is a triple bond. Triple bonds contain three shared pairs of electrons, leading to a significant amount of energy holding the atoms together. The double bonds in CO₂ and CH₂O are strong, but not as strong as the triple bond in CO.

Ultimately, CO's C-O bond is the strongest because the greater the number of shared electrons, the more robust the bond becomes. This highlights how different types of bonds affect the overall characteristics of a molecule.

Triple bond vs Double bond

An essential distinction in chemical bonding is between triple and double bonds. This involves the number of shared electron pairs and directly influences bond characteristics.

In a triple bond, as seen in the CO molecule, three pairs of electrons are shared between carbon and oxygen. This sharing results in a very strong and short bond because of the extensive overlapping of orbitals. Triple bonds hold atoms together more tightly compared to double bonds, requiring more energy to break.

Double bonds, on the other hand, share only two pairs of electrons, like in CO₂ and CH₂O. They are shorter and stronger than single bonds but not as much as triple bonds. Double bonds provide a moderate bond length and strength, making them unique in the balance they offer between stability and reactivity.

Understanding these differences helps in predicting molecular behavior and stability, especially when comparing similar molecules like CO, CO₂, and CH₂O.