W2013CHM2311 Part 4c Notes

G 1s group orbitals for fhf gos for the uorine atoms

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Construc0ng Group Orbitals for FHF ­ In FHF ­, the two fluorine atoms are terminal atoms and are therefore no longer treated individually. Instead, the AOs of the terminal atoms are combined and treated as group orbitals or SALCs. F H F To form GOs for the fluorine atoms, all of the same in ­phase and out ­of ­phase combina0ons of the fluorine wave func0ons that would be considered in crea0ng a F2 molecule must be taken into account. The only difference is now the fluorine orbitals are separated by a central atom, so they cannot form MOs. In FHF ­, since hydrogen is the central atom, only one orbital needs to be considered (e.g., 1s).  ­ Group Orbitals for FHF GOs for the fluorine atoms of FHF ­ ϕA - ϕB ϕA + ϕB 2p 2s F H F 2p 2s F H F  ­ Group Orbitals for FHF Important Points: ➝  The GOs ONLY involve the orbitals of fluorine (non ­central atoms), NOT the hydrogen (central atom) orbitals. The fluorine atoms are not directly bonded to each other, but are separated by a central hydrogen atom. ➝  The fluorine atoms and orbitals can no longer be treated independently. They must always be considered in the form of the group orbitals. ➝  # GOs = # atomic orbitals ↳  In this case, eight fluorine orbitals (each fluorine contributes a 2s, 2px, 2py, 2pz) combine to form eight GOs. Combining the Group Orbitals and the Central Atom We now have two sets of orbitals (these are called the basis orbitals): ↳  Set 1: Atomic orbitals of central atom ↳  Set 2: Group orbitals of terminal atoms The AOs of hydrogen will combine with the GOs of fluorine to generate the molecular orbitals of FHF ­. Just as in the case of linear diatomics, we must determine which GOs have bonding overlap with which AOs by considering symmetry and energy of the orbitals. Combining Group Orbitals and the Central Atom Energy requirements for bonding overlap: Since the energy level of the fluorine AOs that par0cipate in the forma0on of GOs are so far apart, the energies of the corresponding GOs are considered to be approximately the same as the energies of the isolated atomic orbitals. H 1s F 2s F 2p  ­13.6 eV  ­46.4 eV  ­18.7 eV The fluorine 2s GOs are too low in energy to interact with the hydrogen 1s orbital (ΔE = 32.8 eV). The fluorine 2s GOs will therefore not par0cipate in bonding – i.e., these GOs will form nonbonding orbitals. Based on energy requirements, the only possible combina0ons will involve overlap of hydrogen 1s with fluorine 2p. These combina0ons now must be considered in terms of symmetry requirements.  ­ Group Orbitals for FHF Which GOs for the fluorine atoms of FHF ­ will interact with H 1s? ϕA - ϕB ϕA + ϕB...
View Full Document

This note was uploaded on 03/28/2014 for the course CHM 2311 taught by Professor Richardson during the Winter '09 term at University of Ottawa.

Ask a homework question - tutors are online