Question

Give the bond order for each bond in the following molecules or ions: (a) \(\mathrm{CH}_{2} \mathrm{O}\) (b) \(\mathrm{SO}_{3}^{2-}\) (c) \(\mathrm{NO}_{2}^{+}\) (d) NOCl

Short answer

(a) 2, (b) 1.33, (c) 1.5, (d) 2 for specified bonds.

Step-by-step solution

Understand Bond Order Concept

Bond order is calculated as the difference between the number of bonding electrons and antibonding electrons, divided by two, in the Lewis structure. It can also be determined from the number of bonds in the actual structure of molecules or resonance structures.

Draw Lewis Structures

Draw the Lewis structures for each molecule or ion.(a) \(\mathrm{CH}_{2} \mathrm{O}\): C is double-bonded to O and single-bonded to two H atoms.(b) \(\mathrm{SO}_{3}^{2-}\): S forms resonance structures with three O atoms, with one single and two double bonds shared among them.(c) \(\mathrm{NO}_{2}^{+}\): N is bonded to O by a double bond and a single bond shared across resonance structures.(d) NOCl: N is double-bonded to O and single bonded to Cl.

Calculate Bond Order for Each Molecule

(a) \(\mathrm{CH}_{2} \mathrm{O}\): The C=O bond order is 2, since there is one double bond.(b) \(\mathrm{SO}_{3}^{2-}\): Average bond order is calculated considering the resonance structures: 1 single bond and 2 double bonds (4 total bonds/3 oxygens) gives a bond order of 1.33.(c) \(\mathrm{NO}_{2}^{+}\): Average bond order is calculated across its resonance structures, resulting in 1.5.(d) NOCl: The bond order between N and O is 2 due to the double bond.

Summarize Bond Orders

Summarize the bond orders found:(a) \(\mathrm{CH}_{2} \mathrm{O}\): C=O bond order is 2.(b) \(\mathrm{SO}_{3}^{2-}\): Average S-O bond order is 1.33.(c) \(\mathrm{NO}_{2}^{+}\): N-O bond order is 1.5.(d) NOCl: N-O bond order is 2.

Key concepts

Lewis structures

Lewis structures serve as a vital tool in understanding the arrangement of atoms and electrons within a molecule. They provide a visual representation of the valence electrons for each atom, often using dots to symbolize these electrons.
Drawing a Lewis structure involves a few essential steps:

• Determine the total number of valence electrons available based on the atomic composition of the molecule.
• Create a skeleton structure by arranging the atoms around a central atom, usually the least electronegative one (except hydrogen).
• Add pairs of electrons as bonds between atoms to satisfy bonding requirements.
• Distribute the remaining electrons to satisfy the octet rule, placing them as lone pairs or additional bonds as needed.

Through these steps, we can visualize how electrons are shared or transferred, forming various molecular structures with implications for bond order, which is crucial in chemistry.

resonance structures

Resonance structures are an essential concept when considering molecules with more than one valid Lewis structure. They allow for a true depiction of electrons distributed across several possible configurations.
For instance, \(\mathrm{SO}_{3}^{2-}\), with sulfur's bonds to oxygen, displays resonance by alternating single and double bonds among the oxygens.
Distinct details about resonance structures include:

• They are not real structures but a way to represent the extended structure's electron delocalization.
• The actual molecule is better described as a resonance hybrid, possessing characteristics of all possible structures.
• Resonance influences properties like bond length, with each bond in a resonance hybrid adopting an average length.

This ability to stabilize charge across a molecule is what makes understanding resonance crucial for predicting molecular behavior.

bonding electrons

Bonding electrons are those valence electrons that participate in forming chemical bonds between atoms. In a Lewis structure, these are typically visualized as shared pairs, illustrating either single, double, or triple bonds.
Some key points about bonding electrons include:

• They are integral in forming covalent bonds, "gluing" atoms together and creating molecules with a rigid structure.
• Each bond formation represents two bonding electrons, establishing stability and determining properties like bond strength and length.
• Understanding bonding electrons helps us gauge the bond order which plays a critical role in characterizing the molecule's reactivity and interactions.

By examining bonding electrons within a molecule, we gain insights into how atoms maintain their bonded state and dictate molecular properties.

antibonding electrons

Antibonding electrons arise in molecular orbital theory and are conceptualized as those electrons that slightly destabilize a molecule. They occupy antibonding orbitals and typically counteract the stabilization gained by bonding electrons.
Important aspects include:

• These electrons are found in higher energy states compared to bonding electrons.
• Antibonding orbitals are denoted by an asterisk (\(^*\)) in notations like \(\sigma^*\) or \(\pi^*\).
• When calculating bond order, the presence of antibonding electrons decreases the effective order, impacting the molecule’s stability.

Recognizing the role of antibonding electrons is crucial in accurately determining bond order, helping predict a molecule's stability and conceivable decomposition or reaction pathways.