Question

The CO bond length is least in which one of the following? (a) Acetone (b) Carbonate ion (c) Carbon dioxide (d) Carbon monoxide

Short answer

Carbon monoxide (d) has the shortest CO bond length due to its triple bond.

Step-by-step solution

Understand Bond Length Concept

The bond length refers to the average distance between the nuclei of two bonded atoms. Generally, the stronger the bond (e.g., triple bond compared to double or single bond), the shorter the bond length will be.

Analyze Each Option's Bond Structure

Examine the bond structure associated with each option: - Acetone ( ext{CH}_3 ext{COCH}_3) contains a C=O double bond. - Carbonate ion ( ext{CO}_3^{2-}) has resonance structures contributing to an effective bond order between single and double bonds. - Carbon dioxide ( ext{CO}_2) has double bonds between carbon and oxygen atoms. - Carbon monoxide ( ext{CO}) has a triple bond between the carbon and oxygen atoms.

Compare Bond Orders

The bond order relates directly to bond length; higher bond orders correlate with shorter bond lengths. - In acetone, the C=O bond is a double bond. - In the carbonate ion, due to resonance, the average bond order is about 1.33. - In carbon dioxide, each C=O is a separate double bond. - In carbon monoxide, the bond is a triple bond, giving it the highest bond order.

Determine Shortest Bond Length

Since bond length is inversely related to bond order, the structure with the highest bond order will have the shortest bond length. Carbon monoxide, with a triple bond, has the highest bond order among the options.

Key concepts

Bond Length Concept

The term 'bond length' refers to the average distance between the nuclei of two bonded atoms. It reflects not only the size of the atoms but also the type of bond joining them. Understanding bond length is crucial because it affects molecular stability, reactivity, and properties. A shorter bond length generally indicates a stronger and more stable bond due to increased effective nuclear attraction. For chemistry students, comprehending this link between bond length and bonding strength helps explain why molecules behave the way they do.

• Single bonds typically have longer bond lengths and are less strong.
• Double bonds are shorter and stronger than single bonds.
• Triple bonds are the shortest and strongest due to three pairs of shared electrons.

Studying bond length offers insights into various chemical reactions and molecular structures.

Bond Order

Bond order is a fundamental concept that measures the number of chemical bonds between a pair of atoms. This number indicates the degree of bond stability and also points towards bond length.
A higher bond order implies a stronger bond, holding the atoms more closely together, resulting in a shorter bond length. Hence, knowing the bond order aids in predicting the molecule's geometry and reactivity. For instance:

• If an atom pair has a single bond, its bond order is 1.
• A double bond translates to a bond order of 2.
• A triple bond has a bond order of 3, indicating the shortest distance between the bonded atoms.

These increments manifest as increased electron sharing, contributing to bond strength and reduced bond length.

Triple vs Double Bonds

When comparing triple bonds to double bonds, the distinction in electron sharing is key. A double bond consists of one sigma bond and one pi bond, involving a total of four electrons shared between the atoms. Conversely, a triple bond consists of one sigma bond and two pi bonds, sharing six electrons.
As a result, triple bonds are inherently more robust than double bonds, pulling the bonded atoms closer together and significantly shortening the bond length. This difference impacts the molecular properties such as rigidity and reactivity.

• Double bonds show greater flexibility in chemical reactions, forming a variety of isomers.
• Triple bonds typically restrict rotation around the bond axis, lending the molecule more stiffness.

In summary, the increased electron interaction in triple bonds accounts for greater bond strength and shorter bond lengths.

Molecular Structure Analysis

Analyzing molecular structure involves examining the spatial arrangement and connections between atoms within a molecule. This is crucial for predicting chemical behavior and properties.
Bond lengths, along with bond angles, provide clues about the molecule's geometry and influence on reactivity. When a molecule's bond structure is known, its bond orders can be deduced, offering insights into its overall stability.

• Identifying bond types aids in understanding possible molecular interactions.
• Resonance structures reveal the electron distribution and can affect perceived bond order.

Through molecular structure analysis, one can predict physical and chemical behaviors of compounds, facilitating various applications in chemistry, from synthesis to material property evaluation.