Problem 106 - A Complete Resource Book in Chemistry for JEE Main

Question

Bond order of nitric oxide is (a) 1 (b) \(2.5\) (c) 2 (d) \(1.5\)

Step-by-Step Solution

Answer

The bond order of nitric oxide (NO) is 2.5.

Step 1: Understanding Bond Order

Bond order indicates the stability of a bond, showing the number of chemical bonds between a pair of atoms. Bond order is calculated as: \[ \text{Bond Order} = \frac{1}{2} \times (\text{Number of Bonding Electrons} - \text{Number of Antibonding Electrons}) \].

Step 2: Molecular Orbital Diagram for NO

For nitric oxide (NO), populate the molecular orbital diagram: NO has 15 electrons. In the order of molecular orbitals, NO would fill as follows: \(\sigma(1s)^2, \sigma^*(1s)^2, \sigma(2s)^2, \sigma^*(2s)^2, \sigma(2p_z)^2, \pi(2p_x)^2=\pi(2p_y)^2, \pi^*(2p_x)^2, \pi^*(2p_y)^1\).

Step 3: Counting Electrons

Identify the electrons in bonding and antibonding orbitals. Bonding orbitals \((\sigma(2p_z), \pi(2p_x), \pi(2p_y))\) have 8 electrons combined, and antibonding orbitals \((\pi^*(2p_x), \pi^*(2p_y))\) have 3 electrons combined.

Step 4: Calculating Bond Order

Use the formula from Step 1 to calculate the bond order of NO. \[ \text{Bond Order} = \frac{1}{2} \times (\text{8 bonding electrons} - \text{3 antibonding electrons}) = \frac{1}{2} \times 5 = 2.5 \].

Step 5: Selecting the Correct Option

Based on the calculation, the bond order of NO is 2.5. Therefore, option (b) 2.5 is the correct answer.

Key Concepts

Molecular Orbital Theory

Molecular Orbital Theory (MOT) is a fundamental concept in understanding how atoms combine to form molecules. This theory helps us visualize how atomic orbitals come together to form molecular orbitals, which can hold the electrons in a molecule. In the molecular orbital model, electrons are not confined to single atoms or localized bonds. Instead, they are spread over the entire molecule, giving them more freedom and creating detailed electronic structures.

The process involves combining atomic orbitals from each atom involved in the bond. These combinations produce molecular orbitals, which are classified as either 'bonding' or 'antibonding'. Bonding orbitals are lower in energy and help to stabilize the molecule, while antibonding orbitals are higher in energy and can destabilize it. The basic idea is that when electrons occupy bonding orbitals, they contribute to the bond between atoms, but when electrons occupy antibonding orbitals, they weaken that bond.

By understanding how many electrons are in each type of orbital, one can determine the bond order of a molecule, a measure of bond stability. Molecular Orbital Theory thus provides insights into the electronic arrangement and properties of complex molecules such as nitric oxide.

Nitric Oxide

Nitric Oxide (NO) is an interesting molecule that showcases unique bonding characteristics. It is composed of one nitrogen atom and one oxygen atom and is notable for having an odd number of electrons – 15 in total. This makes it a radical, meaning it contains at least one unpaired electron, which contributes to its reactivity.

When analyzing NO using Molecular Orbital Theory, electron distribution across the available orbitals is crucial. By filling the molecular orbitals in energy order, NO forms a specific electron configuration. Starting from the lowest energy level, both bonding and antibonding orbitals get filled according to the available electrons. The unique arrangement of electrons in these orbitals, particularly the presence of both paired and unpaired electrons, contributes to the chemical behavior and bond properties of nitric oxide.

Despite its simplicity, nitric oxide plays a significant role in various chemical processes; it acts as a signaling molecule in biological systems and also participates in atmospheric reactions. Its unusual reactivity and electronic structure provide an excellent example of how molecular orbital theory can be applied to understand real-world molecules.

Bonding and Antibonding Electrons

Electrons in a molecule are distributed across different molecular orbitals that can be broadly categorized into bonding and antibonding orbitals.

• Bonding Electrons: These electrons reside in the lower energy 'bonding' orbitals. They are responsible for holding the atoms together and contribute positively to the bond strength. The more electrons in these orbitals, the stronger and more stable the bond tends to be.
• Antibonding Electrons: These electrons are in the higher energy 'antibonding' orbitals. Unlike bonding electrons, they counteract binding forces, leading to a decrease in bond strength. Having more antibonding electrons can significantly weaken or even destabilize a bond.

In the context of nitric oxide, after appropriately populating its molecular orbitals, there are 8 bonding electrons and 3 antibonding electrons. The concept of bond order, derived from these numbers, shows the net effect of bonding versus antibonding influences. The formula for bond order is given by \[ \text{Bond Order} = \frac{1}{2} \times (\text{Number of Bonding Electrons} - \text{Number of Antibonding Electrons}) \]For nitric oxide, the calculated bond order is 2.5, indicating a fairly strong bond with both stable and unstable electron contributions. Understanding the interplay of bonding and antibonding electrons provide insight into molecular stability and reactivity.