And Crystal Field Theory,
we'll abbreviate CFT.
And Crystal Theory is solely based on
An electrostatic model.
And essentially what we are saying
here in crystal field theory is,
most of these ligands are Lewis basis.
They're electron pair donors.
So, they have these lone
pairs that they're gonna
donate to the transition metal center.
The transition metal
center found the nucleus,
I have a bunch of protons in the nucleus.
But there's a lot of electrons
along the outside of this.
So, when this lone pair starts
to interact with the electrons
on the transition metal,
we have two electrons coming together.
Two electrons coming together in
the same place, is that good or bad?
People are shaking their head,
no, it's bad, right?
There's gonna be a repulsion.
So, when that repulsion happens,
the orbitals are gonna go up in energy.
Where they're only going
to become more unstable, so
what Crystal field theory does is
it only treats, The anti-bonding
Molecular orbitals,
which I'll abbreviate MO and ignores
Bonding And non bonding
Molecular orbitals and this is gonna
make our life so much simpler.
So, we're just looking at these
high energy anti-bonding orbitals.
And we can rationalize through this by
saying there's gonna be some kind of
electron-electron repulsion.
Okay?
There's also gonna be a force
of attraction that causes
those bonding orbitals to go
really far down in energy.
But those orbitals don't really come
into play when we talk about color or
when we talk about magnetism, so,
we're gonna completely ignore those.
Okay?
So, this crystal field theory
is great in terms of explaining
a lot of the physical properties
that we're looking at.
So, what we can say about
this now is that according to
Crystal field theory, the energies
Of transition
metal D orbitals,
after they interact
with a set of Ligands.
Is a function Of
the relative positions
of the ligands and
the individual
D orbitals.
So, what this is basically telling us is
that when we're analyzing these complexes,
and when we're analyzing the excitations
that occur in these complexes.
There's two things that we
really have to consider.
The first thing that we have to consider
is the shape of the d orbitals,
and the second thing that we have
to consider is the arrangement
Of the ligands around the central atom.
Because when these bonds form,
the orbitals are gonna overlap.
We're gonna consider this ligands
more like these spheres or
these bunch of lone pairs pointing
at the transition metal sensor.
But we need to know the shape of the d
orbitals, and we need to know, kind of
where these ligands are pointing,
in order to quantify
this overlap and remember we were
talking back earlier in this unit
about the electromagnetic spectrum and
it spans this large range.
And the visible part of the spectrum is
this tiny little sliver in the middle.
It just so happens that when
a ligand interacts with a d orbital,
the splitting or the difference in
energy between the resulting D orbitals
is right in that little sliver
of the visible portion of
the electromagnetic spectrum, and
this leads to some fascinating properties.
So, we need to know the orbital shapes,
and
we need to know where the ligands
are positioned and what their geometry is.
