Question

(a) What is the difference between hybrid orbitals and molecular orbitals? (b) How many electrons can be placed into each MO of a molecule? (c) Can antibonding molecular orbitals have electrons in them?

Short answer

(a) Hybrid orbitals are formed by the combination of atomic orbitals within the same atom, while molecular orbitals result from the combination or overlapping of atomic orbitals from different atoms in a molecule. (b) Each molecular orbital can accommodate up to 2 electrons, with opposite spins. (c) Yes, antibonding molecular orbitals can have electrons in them, but they weaken the bond between atoms or contribute to repulsion and reduce the stability of the molecule.

Step-by-step solution

(a) Difference between Hybrid Orbitals and Molecular Orbitals

Hybrid orbitals are formed by the combination of atomic orbitals within the same atom, resulting in a new set of equivalent orbitals with specific geometries. These hybrid orbitals help to explain the observed molecular shapes and bond angles in molecules. An example of hybrid orbital formation is the combination of 2s and three 2p orbitals in carbon to form four equivalent sp^3 hybrid orbitals. Molecular orbitals, on the other hand, result from the combination or overlapping of atomic orbitals from different atoms in a molecule. The number of molecular orbitals formed is equal to the number of atomic orbitals that are combined. There are two types of molecular orbitals: bonding molecular orbitals (formed by constructive interference of atomic orbitals) and antibonding molecular orbitals (formed by destructive interference of atomic orbitals).

(b) Electron Placement in Molecular Orbitals

According to molecular orbital theory, each molecular orbital can accommodate up to 2 electrons, with opposite spins (spin-up and spin-down). This principle is the same as the one that governs the placement of electrons in atomic orbitals.

(c) Antibonding Molecular Orbitals

Yes, antibonding molecular orbitals can have electrons in them. However, it is important to note that when electrons occupy an antibonding molecular orbital, they weaken the bond between atoms or even contribute to repulsion. The presence of electrons in the antibonding molecular orbital increases the overall energy of the molecule and reduces its stability. In general, if there are more electrons in bonding molecular orbitals than in antibonding molecular orbitals, the atoms will be bound together in a stable molecule, but if the antibonding molecular orbitals dominate, it is less likely that a stable molecule will form.