Consider HCI molecule:
i) Sketch a Lewis diagram of HCI.
ii) Draw a fully labelled Molecular Orbital diagram for HCI.
iii) Calculate the bond order for HCI. Justify whether the bond order matches the proposed Lewis structure in b) i).
iv) State the number of nonbonding electron pair(s) in this molecule.
v) Relate the number(s) of bonding electron between the Lewis structure and Molecular Orbital diagram of HCI.
The correct answer and explanation is :
Hydrogen chloride (HCl) is a diatomic molecule consisting of a hydrogen atom bonded to a chlorine atom. Let’s address each part of the question:
i) Lewis Structure of HCl:
The Lewis structure represents the valence electrons of atoms within a molecule. For HCl, hydrogen has one valence electron, and chlorine has seven. When they form a covalent bond, they share a pair of electrons, resulting in the following Lewis structure:
H : Cl with three lone pairs on chlorine.
This indicates a single bond between hydrogen and chlorine, with chlorine having three lone pairs of electrons.
ii) Molecular Orbital (MO) Diagram for HCl:
In heteronuclear diatomic molecules like HCl, the atomic orbitals combine to form molecular orbitals. Hydrogen’s 1s orbital interacts with chlorine’s 3p orbital (specifically the 3p_z orbital aligned along the internuclear axis) to form sigma (σ) bonding and antibonding (σ*) molecular orbitals.
The MO diagram can be represented as follows:
Cl 3p_z (σ*)
↑
↑
↑
Cl 3p_z (σ) H 1s
↓
↓
↓
Cl 3s
Here, the hydrogen 1s orbital overlaps with the chlorine 3p_z orbital to form the σ bonding orbital, while the corresponding antibonding σ* orbital remains unoccupied.
iii) Bond Order Calculation:
Bond order is calculated using the formula:
Bond Order = (Number of bonding electrons – Number of antibonding electrons) / 2
In HCl:
- Bonding electrons: 2 (in the σ bonding orbital)
- Antibonding electrons: 0
Bond Order = (2 – 0) / 2 = 1
This bond order of 1 aligns with the single bond depicted in the Lewis structure.
iv) Number of Nonbonding Electron Pairs:
Chlorine has three lone pairs (nonbonding pairs) of electrons in HCl. Hydrogen has no lone pairs.
v) Comparison of Bonding Electrons in Lewis Structure and MO Diagram:
Both the Lewis structure and the MO diagram indicate a single bond between hydrogen and chlorine, involving two bonding electrons. The Lewis structure shows this as a shared pair of electrons, while the MO diagram represents it as electrons occupying the σ bonding molecular orbital.
In summary, the Lewis structure and molecular orbital diagram of HCl both depict a single covalent bond between hydrogen and chlorine, with chlorine possessing three lone pairs of electrons. The bond order calculation confirms the presence of a single bond, consistent with both representations.
For a visual representation of the Lewis structure and MO diagram of HCl, you can refer to the following resources:
- Lewis Structure of HCl:
- Molecular Orbital Diagram of HCl:
These resources provide detailed visualizations to enhance understanding of HCl’s bonding structure.