Which of the following is the correct order of bond length?
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For bond length comparison, first check \textbf{bond order}, then \textbf{atomic size}.
Small atoms like hydrogen can form extremely short bonds even if the bond is single.
Concept:
Bond length is the average distance between the nuclei of two atoms joined by a chemical bond. It mainly depends on:
Bond order: Higher bond order results in a shorter bond length.
Atomic size: Bonds involving smaller atoms are shorter.
Nature of the bond: Triple bonds are shorter than double bonds, and double bonds are shorter than single bonds.
Hence, the general order is:
\[
\text{Triple bond}<\text{Double bond}<\text{Single bond}
\]
Step 1: Examine each bond separately.
\(C–H\):
Although it is a single bond, hydrogen is the smallest atom. Due to its very small atomic radius, the C–H bond length is quite short, even shorter than many multiple bonds involving larger atoms.
\(C\equivN\):
This is a triple bond between carbon and nitrogen. The high bond order (3) causes strong nuclear attraction, leading to a short bond length.
\(C=O\):
This is a double bond with bond order 2. Its bond length is therefore longer than a triple bond but shorter than a single bond.
\(C–O\):
This is a single bond having bond order 1. Single bonds involve the least orbital overlap and hence have the greatest bond length among the given options.
Step 2: Compare the bonds using bond order and atomic size.
Shortest bond: \(\text{C–H}\) (very small size of hydrogen)
Next: \(\text{C}\equiv\text{N}\) (triple bond)
Next: \(\text{C}=\text{O}\) (double bond)
Longest: \(\text{C–O}\) (single bond)
Step 3: Increasing order of bond length:
\[
\text{C–H}<\text{C}\equiv\text{N}<\text{C}=\text{O}<\text{C–O}
\]
This sequence exactly corresponds to Option (A).
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