Electrons anti-bonding orbitals

Jorgensen CK (1975) Partly Filled Shells Constituting Anti-bonding Orbitals with Higher Ionization Energy than Their Bonding Counterparts. 22 49-81 Jorgensen CK (1975) Photo-Electron Spectra of Non-Metallic Solids and Consequences for Quantum Chemistry. 24 1-58... 

Much theoretical work went into trying to understand these results more completely. Newns constructed a simple ID model that incorporated the idea of electrons hopping in and out of the tt anti-bonding orbital of NO as the means by which hot electron-hole pairs could transfer energy to the NO molecule.26 Using reasonable assumption, he was able to quantitatively reproduce the experimentally-observed surface temperature and incidence energy dependence. 

Figure 16.1 The chemical hardness of an atom, molecule, or ion is defined to be half. The value of the energy gap between the bonding orbitals (HOMO—highest orbitals occupied by electrons), and the anti-bonding orbitals (LUMO—lowest orbitals unoccupied by electrons). The zero level is the vacumn level, so I is the ionization energy, and A is the electron affinity, (a) For hard molecules the gap is large (b) it is small for soft molecules. The solid circles represent valence electrons. Adapted from Atkins (1991).

The bonding in the XeF2 molecule can be explained quite simply in terms of a 3-center, 4 electron bond that spans all three atoms in the molecule. The bonding in this molecular orbital description involves the filled 5pz orbital of Xe and the half-filled 2pz orbitals of the two F-atoms. The linear combination of these three atomic orbitals affords one bonding, one non-bonding and one anti-bonding orbital, as depicted below ... 

Lewis acid sites have empty orbitals able to accept electron density from the occupied orbitals of a Lewis base, in parallel with back-donation from the catalyst to the empty anti-bonding orbitals of the base [33]. This interaction leads to the formation of an activated acid-base adduct. In the case of alkanes activation may proceed by hydride abstraction [38]. Y and Beta are good examples of zeolites with Lewis acidity, often quite significant for catalysis [39, 40]. 

Your plots should be similar to those shown in Figure 3.4. That figure shows that there is a building-up of electron probability in I the internuclear region for the bonding orbital, and that there is zero probability in the bond centre for the anti-bonding orbital. 

Then substitute the value for N, from equation 3.21 to give the final equation for the energy of an electron in the anti-bonding orbital ... 

A S, is isoelectronic with O, and therefore has a bond order of 2. The molecule should be paramagnetic since it has two unpaired electrons in the ng anti-bonding orbitals. 

The NF3 molecule has two extra electrons, compared to BF3, which would occupy an anti-bonding 7t-type 2a/ orbital if it had a trigonally planar shape. The C1F3 molecule with another two electrons would make use of the anti-bonding or-type 4a,7 orbital if the molecule were to be trigonally planar. It is to avoid use of anti-bonding orbitals that they adopt different symmetries. 

The high electrical conductivity of lithium (and metals in general) indicates considerable electron mobility. This is consistent with the MO treatment of an infinite three-dimensional array of atoms, in which the 2s orbitals are completely delocalized over the system with the formation of a band of nil bonding orbitals and nil anti-bonding orbitals for the n atoms concerned. Figure 7.3 shows a simple representation of the... 

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