Lecture Ten Flashcards
Draw the AO and MO diagram for O2.
Refer to printed lecture notes for answers.
What is bond order?
One measure of how strongly two nuclei interact.
Bond order = 1/2(number of bonding electrons - number of anti-bonding electrons).
If bond order = 1, there is a single bond.
If bond order = 2, there is a double bond.
Etc.
The higher the bond order:
Stronger the bond, the larger the bond enthalpy and the shorter the bond length.
How can one write the electronic configuration for MOs?
E.g. writing the electronic configuration for F2 (omitting core electrons) is written as:
Written in increasing energy levels.
What does paramagnetic and diamagnetic mean?
Paramagnitism - A substance or body that is very weakly attracted by the poles of a magnet, but not retaining any permanent magnetism.
Diamagnetism - A substance or body tending to become magnetized in a direction at 180° to the applied magnetic field.
Compare Valance Bond Theory with Molecular Orbital Theory.
The distinction between the two can be described as either a ‘localised’ orbital model, or a ‘delocalised’ orbital model.
Both models include 8 orbitals, but in VBT each orbital is localised to the atom, while in MO, each orbital speads across the whole molecule.
In which cases can order of MOs change?
MOs with the same symmetry can mix: I.e. σ2s/σ*2s and σ2p/σ*2p.
This effect is greater for the lighter second row diatomics.
This effect is so ectreme for B2, C2 and N2 that the order of the MOs change.
The energy levels of the 2s and 2p atomic orbitals are close in energy for these molecules. This means that the hybrid σ2s and σ2p MOs formed are close enough in energy levels to mix.
