Which of the following diatomic species is predicted to be stable according to molecular orbital theory?

• A. Ne_2
• B. Be_2
• C. O_2
• D. He_2

Answer: (C)

Verified step by step guidance

1. Recall that molecular orbital (MO) theory predicts the stability of diatomic molecules by filling molecular orbitals formed from atomic orbitals of the constituent atoms.
2. Write the electron configurations of each diatomic species and determine the total number of valence electrons for each molecule: Ne_2, Be_2, O_2, and He_2.
3. Construct the molecular orbital diagram for each species, filling the molecular orbitals in order of increasing energy according to the appropriate scheme (for molecules with atomic number less than 8, use the ordering \( \sigma_{2s} < \sigma^*_{2s} < \pi_{2p} < \sigma_{2p} < \pi^*_{2p} < \sigma^*_{2p} \); for others, adjust accordingly).
4. Calculate the bond order for each molecule using the formula: \[ \text{Bond order} = \frac{(\text{number of electrons in bonding MOs}) - (\text{number of electrons in antibonding MOs})}{2} \]. A positive bond order indicates a stable molecule.
5. Compare the bond orders of Ne_2, Be_2, O_2, and He_2. The species with a positive bond order and unpaired electrons consistent with known paramagnetism (like O_2) is predicted to be stable according to MO theory.