Problem 192 - A Complete Resource Book in Chemistry for JEE Main

Question

The bond order in \(\mathrm{NO}\) is \(2.5\) while that in \(\mathrm{NO}^{+}\)is 3 . Which of the following statements is true for these two species? [2004] (a) bond length in \(\mathrm{NO}^{+}\)is greater than in NO (b) bond length in \(\mathrm{NO}\) is greater than in \(\mathrm{NO}^{+}\) (c) bond length in \(\mathrm{NO}^{+}\)is equal than in NO (d) bond length is unpredictable

Step-by-Step Solution

Answer

(b) bond length in NO is greater than in NO⁺.

Step 1: Understanding Bond Order

The bond order is a measure of the number of chemical bonds between a pair of atoms. It is calculated as the difference between the number of bonding electrons and antibonding electrons, divided by two. Generally, a higher bond order indicates a stronger, shorter bond.

Step 2: Comparing Bond Orders

We're given that the bond order for NO is 2.5 and for NO⁺ it is 3. Higher bond order corresponds to a shorter bond length because more bonding interaction leads to stronger attraction between the two atoms.

Step 3: Evaluating Bond Lengths

Since the bond order for NO⁺ is greater than that of NO (3 > 2.5), the bond in NO⁺ is stronger and thus shorter than in NO. Consequently, the bond length in NO is greater than that in NO⁺.

Step 4: Determining the Correct Statement

The correct statement must reflect that the bond with the greater bond order (NO⁺) has a shorter bond length. Therefore, the correct option is (b) bond length in NO is greater than in NO⁺.

Key Concepts

Bond Length

In chemistry, bond length is the average distance between the nuclei of two bonded atoms. This measurement is crucial because it provides information about the strength and type of a chemical bond. Generally, shorter bond lengths correspond to stronger bonds. This is because the atoms are held together more tightly.
Several factors affect bond length, including:

• Bond order: Higher bond order means more shared electrons between atoms, resulting in shorter bonds.
• Atomic size: Larger atoms will generally form longer bonds.
• Electronegativity: Differences in electronegativity can affect bond length, with more polar bonds often being shorter.

For example, in the case of nitrogen monoxide (NO) and its ionized form (NO⁺), NO has a bond order of 2.5, while NO⁺ has a bond order of 3. The higher bond order in NO⁺ suggests a stronger and thus shorter bond length compared to NO.

Chemical Bonds

Chemical bonds are the attractive forces holding atoms together in molecules and compounds. They form due to interactions between the electrons of atoms.
There are three primary types of chemical bonds:

• Ionic bonds: Formed when electrons are transferred from one atom to another, creating ions that attract each other.
• Covalent bonds: Occur when two atoms share one or more pairs of electrons.
• Metallic bonds: Consist of a lattice of cations surrounded by a 'sea' of delocalized electrons, typical in metals.

The bond order mentioned in the case of NO and NO⁺ refers to covalent bonds. A higher bond order implies more shared electron pairs, leading to a stronger covalent bond. For instance, NO⁺ with a bond order of 3 implies a triple bond, indicating three shared pairs of electrons.

Molecular Structure

Molecular structure defines the arrangement of atoms within a molecule. This structure dictates not only the shape and size of the molecule but also its chemical reactivity and properties.
Several factors influence molecular structure:

• Bond angles: The angles between adjacent bonds influence the molecule's shape.
• Bond lengths: Shorter bonds lead to more compact molecular structures.
• Hybridization: The mixing of atomic orbitals influences molecular geometry.

The structure of NO and NO⁺ is influenced by their bond orders. NO, with a bond order of 2.5, typically exhibits a bond length indicative of somewhat lesser electron sharing compared to NO⁺, which has a bond order of 3. Consequently, NO⁺ is more compact, reflecting these stronger interactions and affecting how the molecule behaves chemically.