Chemistry - CHEMICAL BONDING Question with Solution | TestHub
Four independent models are supplied. I: an intrinsic semiconductor has a filled valence band and empty conduction band at0K, separated by a small gap. II: in a metal carbonyl, metal→CO back donation fills ligand π* orbitals. III: absorption of visible light requires an allowed gap within the visible photon-energy range. IV: NO has eleven valence electrons with one π* electron. Which deductions are correct?
Options:(select one or more)
Answer:
Solution:
Thermal promotion across the small gap produces electron-hole carriers inI. Back donation populates CO antibonding orbitals, weakening and lengthening C–O and lowering its stretching frequency, so B reverses the effect. A UV-only transition does not by itself absorb visible photons, giving C. NO→NO⁺ removes an antibonding electron: BO increases2.5→3 and the electron count becomes closed-shell in the stated MO picture. All four deductions require keeping the separate band, ligand and molecular-antibonding models distinct.
