Symmetry, Overlap, Energy (SOE)

TP C2 is diamagnetic. From this we can conclude the following about the relative stability of the 2 bonding MO’s. 33% 1. 2pσ is more stable than 2pπ 33% 2. 2pπ is more stable than 2pσ 33% 3. Further information is still required TP B2 is paramagnetic. From this we can conclude the following about the relative stability of the 2p bonding MO’s. 33% 1. 2pσ is more stable than 2pπ 33% 2. 2pπ is more stable than 2pσ 33% 3. Further information is still required For today: • Complete: B2 to Ne2 • When atoms are different, use Symmetry, Overlap, Energy SOE to decide which AOs combine Only valence AO’s affect bonding/antibonding B2 is paramagnetic. From this we can conclude the following about the relative stability of the 2p bonding MO’s. 1 TP C2 is diamagnetic. From this we can conclude the following about the relative stability of the 2p bonding MO’s. 33% 1. 2pσ is more stable than 2pπ 33% 2. 2pπ is more stable than 2pσ 33% 3. Further information is still required Quiz N2 is diamagnetic. From this we can conclude the following about the relative stability of the 2p bonding MO’s. 33% 1. 2pσ is more stable than 2pπ 33% 2. 2pπ is more stable than 2pσ 33% 3. Further information is still required Only valence AO’s affect bonding/antibonding C2 is diamagnetic. From this we can conclude the following about the relative stability of the 2p bonding MO’s. Only valence AO’s affect bonding/antibonding N2 is diamagnetic. From this we can conclude the following about the relative stability of the 2p bonding MO’s. 2 Homonuclear diatomics, up to Ne2 The relative stability of the 2pσ* and 2pπ* antibonding MO’s is uncertain. TP O2 is paramagnetic. From this we can conclude the following about the relative stability of the 2p antibonding MO’s. Let’s see how we can use the magnetic properties O2, F2, and Ne2 to determine the ordering. 33% 1. 2pσ* is more stable than 2pπ* 33% 2. 2pπ* is more stable than 2pσ* 33% 3. Further information is still required Only valence AO’s affect bonding/antibonding TP F2 is diamagnetic. From this we can conclude the following about the relative stability of the 2p antibonding MO’s. O2 is paramagnetic. From this we can conclude the following about the relative stability of the 2p antibonding MO’s. 33% 1. 2pσ* is more stable than 2pπ* 33% 2. 2pπ* is more stable than 2pσ* 33% 3. Further information is still required 3 Only valence AO’s affect bonding/antibonding F2 is diamagnetic. From this we can conclude the following about the relative stability of the 2p antibonding MO’s. Only valence AO’s affect bonding/antibonding TP If Ne2 were to exist it would diamagnetic. From this we can conclude the following about the relative stability of the 2p antibonding MO’s. 0% 1. 2pσ* is more stable than 2pπ* 0% 2. 2pπ* is more stable than 2pσ* 0% 3. Further information is still required Homonuclear diatomics If Ne2 were to exist it would diamagnetic. From this we can conclude the following about the relative stability of the 2p antibonding MO’s. 4 When atoms are different, which AO’s combine? When atoms are different, which AO’s combine? As example, let’s consider HO . Use SOE: Symmetry, Overlap, Energy • Symmetry: AO’s must have nonzero overlap • Overlap: AO’s with greatest overlap form MO’s with the greatest bonding/antibonding effect • Energy: AO’s closest in energy form MO’s with the greatest bonding/antibonding effect What AO’s on O combine with H 1s to form the MO’s of HO ? The possibilities O 1s, O 2s, O 2p , O 2p , and O 2p . To decide the optimum pairing, … When atoms are different, which AOs combine? When atoms are different, which AOs combine? They must have appreciable overlap. They must have appreciable overlap. Not OK example: H 1s OK example: H 1s O 1s O 2s 5 When atoms are different, which AO’s combine? When atoms are different, which AO’s combine? They must have the correct symmetry. They must have the correct symmetry. OK example: H 1s Not OK example: H 1s O 2p is bond axis O 2p is perpendicular to bond axis When atoms are different, which AOs combine? When atoms are different, which AOs combine? Based on overlap and symmetry, we need to decide between the two pairings The way to select the optimum pairing is the pairing that is closest in energy. H 1s O 2s H 1s O 2p Here is why. 6 Energy: Closer the better When atoms are different, which AOs combine? They must be close in energy. OK example: H 1s 13.59 eV O 2p 13.62 eV When atoms are different, which AOs combine? When atoms are different, which AOs combine? They must be close in energy. They must be close in energy. Not OK example: H 1s 13.59 eV O 2s 35.12 eV OK example: H 1s 13.59 eV Not OK example: H 1s O 2p 13.59 eV O 2s 13.62 eV 35.12 eV So in HO form MO’s from H 1s and O 2pz 2px and 2py have the wrong symmetry … rather than from H 1s and O 2s. 7