CHEM 150 1nd Edition Chapter 9 : Molecular Geometry and Bonding Theories Lecture 32Outline of Last Lecture • A covalent bond is produced by the overlap of orbitals in the region between the two atoms the greater the overlap, the stronger the bond.• Problem: The atomic orbitals do not always point in the right directions to produce the shapes that we know the molecules have. • To explain this, it is assumed that the atomic orbitals are mixed to produce ‘hybrid’ orbitals that point in the correct direction.• Hybrid orbitals are named from the orbitals that contribute to them: sp2 are a combination of one s and two p orbitals • The orbitals that are mixed must come from the same shell (same value of n).Outline of Current Lecture • When wave functions (orbitals) overlap, they can either: add to form a bonding orbital (constructive interference) or cancel out to form an anti-bonding orbital (destructive interference)• These are no longer atomic orbitals. The are molecular orbitals.• Note that the total number of orbitals is unchanged: two atomic orbitals create twomolecular orbitals• Molecular orbitals can be sigma or pi orbitals. Anti-bonding orbitals are indicated with an asterisk. Current Lecture-Using the idea that each atomic orbital on one atom interacts with its counterpart on the other atom to make a bonding orbital and an anti-bonding orbital, an orbital energy level diagram of the molecule can be drawn.-This only needs to be done for the valence-level orbitals.-Count the total number of valence electrons then fill the orbitals starting at the bottom (lowest energy) molecular orbitals to form the ground state of the molecule.-This theory can be used to predict bond order and magnetic properties.Bond order = 1/2(bonding e- -anti-bonding e-)Unpaired electrons= paramagnetic all paired= diamagnetic Q: Predict bond order and magnetic properties for H2, He, He2+, H2-. H2^2- A:
View Full Document
Unlocking...