Question

Which one of the following molecules contains two 'sigma' ($\sigma$) bonds and two 'pi' ($\pi$) bonds? ________.

• A. $O_{2}$
• B. $N_{2}$
• C. $C_{2}H_{2}$
• D. $CO_{2}$
• E. CO

Hint:

Double bond $= 1\sigma + 1\pi$; Triple bond $= 1\sigma + 2\pi$.

Answer 1

The Correct Option is D

Step 1: Understanding the Concept
This question requires knowledge of how to determine the number of sigma (\(\sigma\)) and pi (\(\pi\)) bonds in a molecule. The type and number of bonds are determined by the molecule's Lewis structure.
- A single covalent bond is always one \(\sigma\) bond.
- A double covalent bond consists of one \(\sigma\) bond and one \(\pi\) bond.
- A triple covalent bond consists of one \(\sigma\) bond and two \(\pi\) bonds.
Step 2: Detailed Explanation
Let's analyze the bonding structure of each molecule.
(A) O\(_2\) (Oxygen): The two oxygen atoms share two pairs of electrons, forming a double bond. The structure is \(O=O\). - Number of \(\sigma\) bonds: 1 - Number of \(\pi\) bonds: 1 (B) N\(_2\) (Nitrogen): The two nitrogen atoms share three pairs of electrons, forming a triple bond. The structure is \(N \equiv N\). - Number of \(\sigma\) bonds: 1 - Number of \(\pi\) bonds: 2 (C) C\(_2\)H\(_2\) (Acetylene): The structure is linear, \(H-C \equiv C-H\). It has two single bonds (C-H) and one triple bond (C\(\equiv\)C). - Sigma bonds: 1 from each C-H bond, and 1 from the C\(\equiv\)C bond. Total \(\sigma\) = 1 + 1 + 1 = 3. - Pi bonds: 2 from the C\(\equiv\)C bond. Total \(\pi\) = 2. (D) CO\(_2\) (Carbon Dioxide): The carbon atom is in the center and forms a double bond with each of the two oxygen atoms. The structure is linear: \(O=C=O\). - Each C=O double bond contains one \(\sigma\) bond and one \(\pi\) bond. - Total \(\sigma\) bonds = 1 (from left C=O) + 1 (from right C=O) = 2. - Total \(\pi\) bonds = 1 (from left C=O) + 1 (from right C=O) = 2. This molecule matches the requirement of two \(\sigma\) bonds and two \(\pi\) bonds. (E) CO (Carbon Monoxide): The carbon and oxygen atoms are joined by a triple bond, \(C \equiv O\). - Number of \(\sigma\) bonds: 1 - Number of \(\pi\) bonds: 2 Step 4: Final Answer
The molecule that contains two sigma bonds and two pi bonds is CO\(_2\).