Use Molecular Orbital Theory to Determine Whether He2²⁺ or He2⁺ is More Stable

To determine the stability of He₂²⁺ and He₂⁺, we can analyze their electronic configurations using Molecular Orbital Theory.

First, let’s establish the molecular orbital diagrams for both ions.

For He₂⁺:

• There are 2 helium atoms. Each helium atom has 2 electrons, giving a total of 4 electrons in neutral He₂.
• Removing one electron for He₂⁺ leaves us with 3 electrons.

The molecular orbitals fill in the following order for He₂:

• σ_1s (2 electrons)
• σ_1s⁻ (1 electron)

So, the electron configuration for He₂⁺ is: σ_1s² σ_1s⁻¹. Since we have 2 electrons in the bonding orbital and 1 in the antibonding orbital, this molecule has a net bond order of
(2 – 1)/2 = 0.5.

For He₂²⁺:

• Removing two electrons for He₂²⁺ leaves us with 2 electrons.

The molecular orbitals fill similarly:

• σ_1s (2 electrons)

So, the electron configuration for He₂²⁺ is: σ_1s². This gives a net bond order of
(2 – 0)/2 = 1.

Comparison of Stability:

A higher bond order indicates greater stability. Therefore:

• He₂²⁺ has a bond order of 1.
• He₂⁺ has a bond order of 0.5.

Based on bond order, He₂²⁺ is more stable than He₂⁺. This is primarily because He₂²⁺ has a complete bonding orbital with no occupancy of antibonding orbitals, leading to a stronger bond. In contrast, He₂⁺ has an electron in an antibonding orbital, which reduces its stability.