Question 9.9: For the O2^+ ion predict (a) number of unpaired electrons, (...
For the O^{+}_{2} ion predict (a) number of unpaired electrons, (b) bond order, (c) bond enthalpy and bond length.
Analyze Our task is to predict several properties of the cation O^{+}_{2}.
Plan We will use the MO description of O^{+}_{2} to determine the desired properties. We must first determine the number of electrons in O^{+}_{2} and then draw its MO energy diagram. The unpaired electrons are those without a partner of opposite spin. The bond order is one-half the difference between the number of bonding and antibonding electrons. After calculating the bond order, we can use Figure 9.40 to estimate the bond enthalpy and bond length.
Solve
(a) The O^{+}_{2} ion has 11 valence electrons, one fewer than O_{2}. The electron removed from O_{2} to form O^{+}_{2} is one of the two unpaired \pi ^{*}_{2p} electrons (see Figure 9.40). Therefore, O^{+}_{2} has one unpaired electron.
(b) The molecule has eight bonding electrons (the same as O_{2}) and three antibonding electrons (one fewer than O_{2}). Thus, its bond order is
(c) The bond order of O^{+}_{2} is between that for O_{2} (bond order 2) and N_{2} (bond order 3). Thus, the bond enthalpy and bond length should be about midway between those for O_{2} and N_{2}, approximately 700 kJ/mol and 115 pm. (The experimentally measured values are 625 kJ/mol and 112.3 pm.)
