Question

The correct increasing order of C-H(A), C-O(B), C=O(C) and C\(\equiv\)N(D) bonds in terms of covalent bond length is :

• A. A \(<\) D \(<\) C \(<\) B
• B. A \(<\) B \(<\) C \(<\) D
• C. D \(<\) C \(<\) B \(<\) A
• D. D \(<\) C \(<\) A \(<\) B

Hint:

Bond order is the dominant factor for bonds between similar-sized atoms: Single \(>\) Double \(>\) Triple in length. However, C-H is exceptionally short because H is in the 1st shell.

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Bond length is determined by the atomic radii of the bonded atoms and the bond order (number of shared electron pairs). Higher bond order leads to shorter bond lengths. Also, Hydrogen is significantly smaller than carbon, oxygen, or nitrogen.

Step 2: Detailed Explanation:
Let's compare the approximate bond lengths:
1. C-H (A): Although it is a single bond, Hydrogen has an extremely small atomic radius. The C-H bond length is typically around \( 109 \text{ pm} \).
2. C\(\equiv\)N (D): This is a triple bond. Even though the atoms are larger than Hydrogen, the high bond order makes it very short, roughly \( 116 \text{ pm} \).
3. C=O (C): This is a double bond. It is longer than a triple bond but shorter than a single bond, roughly \( 121 \text{ pm} \).
4. C-O (B): This is a single bond between two Period 2 atoms. It is the longest among the listed bonds, roughly \( 143 \text{ pm} \).
Comparing the values: \( 109 \text{ pm (A)}<116 \text{ pm (D)}<121 \text{ pm (C)}<143 \text{ pm (B)} \).
The order is A \(<\) D \(<\) C \(<\) B.

Step 3: Final Answer:
The correct order is A \(<\) D \(<\) C \(<\) B.