Bonding and Molecular Orbital Theory

why do bonds form

attractive force between nuclei, interactions lower energy

constructive interference

orbitals in same phase, increase in electron density between nuclei, lower in energy

destructive interference

orbitals in opposite phase, node in between, decrease in electron density, higher in energy

valence bond theory

assumes that electrons in a bond are localized to the atom they come from and only occupy atomic orbitals

is oxygen paramagnetic or diamagnetic?

paramagnetic. valence bond theory says diamagnetic, but from experimentation, we know there are unpaired electrons

rules for forming MOs

1. number of MOs must equal number of atomic orbitals
2. atomic orbitals must have same symmetry
3. put electrons according to Aufbau principle (lowest energy first)
4. atomic orbitals must be relatively close in energy to form an MO

expain how orbital mixing results in σ-π crossover

difference in energy is so small between orbitals, as you go across the second period, the energy gap between 2s and 2p orbitals increases due to the increased effective nuclear charge, which pulls the 2s orbitals to lower energy levels.

in a heterodiatomic MO diagram, the more electronegative atom will have a lower or higher energy atomic orbital?

lower energy orbital

How to assign symmetry to ligand group orbitals

generate a reducible representation, apply each symmetry operation to the set of orbitals, if the atom moves, contributes 0, atom stays and phase is same, contributes 1, atom stays and phase changes, contributes -1, plug into equation to reduce, then determine symmetries

how to determine symmetry of central atom

look at character table, s orbitals are the top row, p orbitals can look at what has x y and z in the column

E symmetry orbitals are ________ degenerate

doubly

explain bonding in SF6

bond order is 4, indicates four of the fluorines are attached and two are nearby anions. 4 bonding MOs are spread across 7 atoms, doesn't actually want to violate the octet rule