Home > Chemistry > Bonus Lecture: Principles of Chemical Science – Lecture 29 Notes

Bonus Lecture: Principles of Chemical Science – Lecture 29 Notes

Overview

Today is a 50 minute lecture on the relevence of crystal field theory.  They are having an exam coming up the next day.

Also, importantly, there is an updated copy of this lecture in 2008.  The edition we’re watching is the 2005 version.  The 2008 version actually shows the slides instead of focusing on the teacher all the time.

Details

Crystal field theory tries to expain experimental data.  Each ligand is considered as a negative point charge.

The tetrahedral case.  The CFSE tends to be smaller, so this is a high spin system.  Here the dx2-y2 and dz2 are stabilized, the others are destabilized at higher energy.  There is a tetrahedral splitting energy.  This is opposite of the octahedral case.

_  _ _ e   +2/5

_ _ t2      -3/5

In high spin, there is the maximum number of unpaired electrons.  Most tetrahedral complexes are high spin.  Put them in singley to the fullest extent.

The square planar case is different.  There is alot of repulsion, so the CFSE is high.  This is a low spin system.

_ dz2

_dx2-y2

_ _ _

A linear molecule along the z axis.  Predict who has the most stabilization and destabilization.

Two different octahedral cases.  Iron surrounded by 6 ligands.

[Fe(H2O)6]

d count = d5 = t2g3 eg2

CFSE = 0 do

CFSE is the energy of stabilization due to the splitting effect.

High spin case, weak splitting field

[Fe(CN)6]

d count = d5 = t2g5

CFSE = -10/5 + 2PE do

Low spin case, strong splitting field

Strong field ligands produce strong splitting fields and splits the d orbitals.  Weak field ligands are the opposite.

SFL : CN-, NH3, CO

IFL: H2O, OH-, F-

WFL: I-, Br-, Cl-

Colors depend upon what photon energies are absorbed.  The color of the transmitted light is complementary to the absorbed light.  High eenrgy is blue light, low energy is red light.

The usefulness of crystal field theory is in explaining the color of transition metal complexes.

splitting energy to the color

Colorless complexes where there are no d d transitions.  The distance is too great.

E = hf

If an enzyme is colored, there is probably a color in it.

smak ki small freq blue

Compounds with unpaired electrons are paramagnetic attracted, paired are repelled diamagnetic, all paired.  Tetrahedral tends to be high spin.

Review

PV = nRT

G = H -TS

k = products/reactants

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