Question 9.8: What is the bond order of the He2^+ ion? Would you expect th...
What is the bond order of the He^{+}_{2} ion? Would you expect this ion to be stable relative to the separated He atom and He^{+} ion?
Analyze We will determine the bond order for the He^{+}_{2} ion and use it to predict whether the ion is stable.
Plan To determine the bond order, we must determine the number of electrons in the molecule and how these electrons populate the available MOs. The valence electrons of He are in the 1s orbital, and the 1s orbitals combine to give an MO diagram like that for H_{2} or He_{2} (Figure 9.30). If the bond order is greater than 0, we expect a bond to exist, and the ion is stable.
Solve The energy-level diagram for the He^{+}_{2} ion is shown in Figure 9.31. This ion has three electrons. Two are placed in the bonding orbital and the third in the antibonding orbital. Thus, the bond order is
Bond order = \frac{1}{2} (2 – 1) = \frac{1}{2}
Because the bond order is greater than 0, we predict the He^{+}_{2} ion to be stable relative to the separated He and He^{+}. Formation of He^{+}_{2} in the gas phase has been demonstrated in laboratory experiments.
