Molecular orbital first-order

In order to write the electron configuration of a molecule, we must first arrange the molecular orbitals in order of increasing energy. Then we can nse the following guidelines to fill the molecnlar orbitals with electrons. The mles also help us understand the stabilities of the molecnlar orbitals. 

So far we have considered only the energies of individual molecular orbitals. In order to determine the energy of a particular structure, we must take into account the number of electrons in each of those MOs. If electrons are placed into the molecular orbitals according to the aufbau principle, the first two electrons go into the lowest energy orbital, the next two electrons go into in the next lowest energy orbital, and so forth. In the case of ethene, there are two... 

How can we justify the difference in ordering of molecular orbitals First of all, we note that for the smaller atoms, the 2s and 2p orbitals are closer in energy than they are for the larger atoms of the second-row atoms. By the reasoning above that only similar-energy atomic orbitals will interact, the smaller atoms will have more... 

HMO theory is named after its developer, Erich Huckel (1896-1980), who published his theory in 1930 [9] partly in order to explain the unusual stability of benzene and other aromatic compounds. Given that digital computers had not yet been invented and that all Hiickel s calculations had to be done by hand, HMO theory necessarily includes many approximations. The first is that only the jr-molecular orbitals of the molecule are considered. This implies that the entire molecular structure is planar (because then a plane of symmetry separates the r-orbitals, which are antisymmetric with respect to this plane, from all others). It also means that only one atomic orbital must be considered for each atom in the r-system (the p-orbital that is antisymmetric with respect to the plane of the molecule) and none at all for atoms (such as hydrogen) that are not involved in the r-system. Huckel then used the technique known as linear combination of atomic orbitals (LCAO) to build these atomic orbitals up into molecular orbitals. This is illustrated in Figure 7-18 for ethylene. 

You can order the molecular orbitals that arc a solution to etjtia-tion (47) accordin g to th eir en ergy, Klectron s popii late the orbitals, with the lowest energy orbitals first. normal, closed-shell, Restricted Hartree hock (RHK) description has a nia.xirnuin of Lw o electrons in each molecular orbital, one with electron spin up and one w ith electron spin down, as sliowm ... 

Figure 7.14 Molecular orbital energy level diagram for first-row homonuclear diatomic molecules. The 2p, 2py, 2p atomic orbitals are degenerate in an atom and have been separated for convenience. (In O2 and F2 the order of

Strategy First, find the number of valence electrons. Then construct an orbital diagram, filling the available molecular orbitals (Figure 3) in order of increasing energy. 

Consider again the electron-transfer reaction O + ne = R the actual electron transfer step involves transfer of the electron between the conduction band of the electrode and a molecular orbital of O or R (e.g., for a reduction, from the conduction band into an unoccupied orbital in O). The rate of the forward (reduction) reaction, Vf, is first order in O ... 

At first sight, the molecular orbital description of N2 looks quite different from the Lewis description ( N=N ). However, it is, in fact, very closely related. We can see their similarity by defining the bond order (b) in molecular orbital theory as the net number of bonds, allowing for the cancellation of bonds by antibonds ... 

Use in first order of the Cl coefficients to correct the occupied and virtual molecular orbitals... 

---