A Quantum Mechanical Progression of Understanding Hydrogen the atom (1 p+, 1 e-) modifications A Quantum Mechanical Progression of Understanding …Zeff and hydrogen-like orbitals Poly-electronic atoms (more than 1 p+ and more than 1 e-) Molecules comprised of atoms (the overlap of e-’s in atomic orbitals…the localized electron model) …resonance / hybridization Molecules from a holistic perspective (more than one nucleus and more than one electron) …molecular orbitals
The simplest molecule... H2 1s 1s
Constructive Overlap 1sA + 1sB electron densities add together
Destructive Overlap 1sA - 1sB electron densities cancel each other
Interaction of two atomic orbitals dictates the production of two molecular orbitals…. s1s* Probability distributions are on either side of nuclei s1s Probability distribution is in between the nuclei
stable molecule H2 s1s2 s1s* E 1s 1s s1s # of bonding e-’s - # of antibonding e-’s Bond Order = 2 s1s* antibonding M.O. E 1s 1s s1s Bond Order probonding M.O. = 1 (molecular orbital configuration notation) H2 s1s2
not a stable molecule He2 s1s* E 1s 1s s1s = 0 Bond Order antibonding probonding = 0 He2
Factors which influence the strength of the interactions between two atomic orbitals which produce 2 molecular orbitals is determined by: A. the energy difference between the orbitals. B. the magnitude of their overlap. In general…for the interaction to be strong…the energies of the orbitals must be ~ equal and the overlap should be large. Li2 Liatom 1s22s1 Liatom 1s22s1
stable molecule Li2 s1s2 s1s*2 s2s2 E Liatom 1s22s1 Liatom 1s22s1 s2s* Bond Order 1s 1s = 1 s1s Li2 Liatom 1s22s1 Liatom 1s22s1