Why Are Options B and C Incorrect for HOMO-LUMO Energy Gap?

[Amitkumarr]

Homework Statement

Which of the following statements is/are correct?

(a) The molecular orbitals are essentially identical to the relevant atomic orbitals at very high energy differences.

(b) Dominantly ionic compounds of group I have HOMO-LUMO energy gap in visible region generally.

(c) Coloured covalent diatomic molecules have HOMO-LUMO energy gap in ultraviolet region.

(d) All of the above.

Relevant Equations

No relevant equations.Based on Molecular orbital theory.

According to me Option A is a correct option because as the energy difference between two atomic orbitals increases,
their interaction, and thus the value of E (or E*) decreases. Here, E is the energy difference between the bonding molecular orbital and the atomic orbital of lower energy , while E* is the energy difference between the antibonding molecular orbital and the higher-energy atomic orbital. As these values decrease, the molecular orbitals become more and more similar to the atomic orbitals from which they are derived.
But what should be the correct answer for options B and C? The HOMO-LUMO energy gap of the given compounds lies in which region?
Note: Answer is given as option A.Why options B and C are wrong?

 

[chemisttree]

Ionic compounds will be colored if the HOMO-LUMO bandgap is of the same energy as visible light. What does this mean to you? What color are Group I ionic compounds, generally? If that bandgap is of the same energy of a photon outside the visible region, will it be colored?

 

[Amitkumarr]

Ionic compounds will be colored if the HOMO-LUMO bandgap is of the same energy as visible light. What does this mean to you? What color are Group I ionic compounds, generally? If that bandgap is of the same energy of a photon outside the visible region, will it be colored?

Group I ionic compounds are generally colorless so,their HOMO-LUMO band gap must lie outside the visible region.If that bandgap is of the same energy of a photon outside the visible region,they will not be colored,right?
Whereas,covalent diatomic molecules which are colored must have their HOMO-LUMO band gap in the visible region.

So,is there any specific region where the HOMO-LUMO band gap of Group I ionic compounds lie(like ultraviolet, infrared etc.)?

 

[chemisttree]

That’s a good question. Try it for yourself!

Remember, E = hv

 

[Amitkumarr]

That’s a good question. Try it for yourself!

Remember, E = hv

Thanks a lot for helping me and for giving me the link.