Why do the electrons placed in antibonding molecular orbital destabilise the molecule? Choose the appropriate answer.

Options

A. In antibonding molecular orbital, the mutual repulsion of the electrons is more than the attraction between the electrons and the nuclel
B. In antibonding molecular orbital, the repulsion between the nuclei is high due to presence of a plane between the nuclei
C. Both (1) and (2)
D. None of the above

Answer

To understand why electrons placed in antibonding molecular orbitals destabilize a molecule, we can break down the explanation into several steps:

### Step 1: Understanding Molecular Orbitals
Molecular orbitals (MOs) are formed when atomic orbitals combine. There are two types of molecular orbitals: bonding and antibonding. Bonding molecular orbitals (MOs) stabilize the molecule, while antibonding MOs can destabilize it.

**Hint:** Remember that bonding MOs are formed by constructive interference, while antibonding MOs result from destructive interference.

### Step 2: Antibonding Molecular Orbitals
Antibonding molecular orbitals are denoted with an asterisk (e.g., σ*). They are formed when atomic orbitals combine in such a way that the wave functions interfere destructively. This means that the electron density is reduced in the region between the nuclei of the bonded atoms.

**Hint:** Focus on the concept of wave functions and how they interact to form molecular orbitals.

### Step 3: Destructive Interference
In an antibonding orbital, the wave functions of the atomic orbitals combine in a way that leads to destructive interference. This results in a node (a region of zero electron density) between the nuclei, meaning that there is a low probability of finding electrons in that region.

**Hint:** Think about how the arrangement of electrons affects the stability of the bond between atoms.

### Step 4: Consequences of Low Electron Density
The low electron density between the nuclei means that there is less attraction between the positively charged nuclei of the atoms. This reduced attraction leads to a destabilization of the molecule because the repulsive forces between the nuclei become more significant compared to the attractive forces.

**Hint:** Consider the balance of attractive and repulsive forces in a molecule.

### Step 5: Overall Effect on Molecular Stability
When electrons occupy antibonding orbitals, they contribute to the destabilization of the molecule. This is because the presence of these electrons increases the energy of the system, making it less stable compared to when electrons are in bonding orbitals.

**Hint:** Reflect on how energy levels relate to the stability of a molecule.

### Conclusion
In summary, electrons placed in antibonding molecular orbitals destabilize the molecule due to destructive interference between electron waves, which leads to low electron density between the nuclei, reducing the attractive forces and increasing the overall energy of the molecule.