Crystal field theory

Question 1

What does the crystal field theory assume?

Answer 1

Ligands are point negative charges and the binding within a complex is purely ionic

Question 2

What phase is it assumed the metal is in?

Answer 2

Gas phase

Question 3

Where are the negatively charged ligands assumed to be from?

Answer 3

infinity

Question 4

When drawing an energy diagram for octahedral complexes, how many orbitals are there before any splitting occurs? How do they compare to each other?

Answer 4

5

They have the same energy - degenerate

Question 5

For an octahedral complex, how many orbitals are high energy? Which ones are they?

Answer 5

2
dz²
dx²-y²

Question 6

What is the high energy level called for octahedral complexes?

Answer 6

eg

Question 7

How many orbitals are low energy for octahedral? Which ones are they?

Answer 7

3
dxy
dyz
dxz

Question 8

What is the low energy level called for octahedral complexes?

Answer 8

t2g

Question 9

What is the gap between eg and t2g called?

Answer 9

ΔO (oct)

Question 10

For the octahedral complex, what is the value from the middle to the eg level?

Answer 10

+3/5 ΔO

Question 11

For the octahedral complex, what is the value from the middle to the t2g level?

Answer 11

-2/5 ΔO

Question 12

What happens when the ligands approach from infinity along the x,y and z axes?

Answer 12

The electrons in the d-orbitals start to sense them

Question 13

Why do dz² and dx²-y² rise in energy?

Answer 13

The negative charges are being brought closer together which means they become destabilised

Question 14

Why are dxy, dxz and dyz not as affected and are lower in energy?

Answer 14

They point in between the axes and are lower in energy

Question 15

In a tetrahedral complex, where do the ligands point?

Answer 15

In between the axes

Question 16

In a tetrahedral complex, which orbitals are better aligned with the ligands?

Answer 16

dxy
dyz
dxz

Question 17

In an octahedral complex, where do the ligands point?

Answer 17

dz² and dx²-y² point along the xyz axes

dxz, dyz and dxy point in between the axes

Question 18

In a tetrahedral complex, which orbitals are high energy?

Answer 18

dxy
dyz
dxz

Question 19

In a tetrahedral complex, which orbitals are low energy?

Answer 19

dz² and dx²-y²

Question 20

In a tetrahedral complex, what is the high energy level called?

Answer 20

t2

Question 21

In a tetrahedral complex, what is the low energy level called?

Answer 21

e

Question 22

Why are the labels for octahedral and tetrahedral complexes different?

Answer 22

There is no symmetry in tetrahedral molecules

the g stands for gerade so it is lost when describing tetrahedral energy levels

Question 23

What is the difference in energy between t2 and e?

Answer 23

Δtet

Question 24

What is the energy gap between the middle and the t2 level?

Answer 24

+2/5Δt

Question 25

What is the energy gap between the middle and the e level?

Answer 25

-3/5Δt

Question 26

How does the splitting term for Δtet compare to Δoct?

Answer 26

Smaller

Question 27

What is a tetragonal distortion?

Answer 27

The two ligands of an octahedral complex along the z-axis are pulled away from the metal to form a square planar complex

Question 28

What does tetragonal distortion remove?

Answer 28

the degeneracy of eg

Question 29

What happens when the two ligands on the z axes of an octahedron complex are removed?

Answer 29

The d-orbitals with a z component lower in energy

Question 30

Why do the d orbitals with an x,y component rise in energy during the formation of a square planar complex?

Answer 30

The ligands in the x-y plane are pulled in more

Question 31

In a square planar complex, when does the dz² orbital fall in energy to below that of the dxy?

Answer 31

Eventually the two ligands are removed to infinity

Question 32

For octahedral complexes, where do you fill the orbitals up from first?

Answer 32

From the bottom | t2g

Question 33

What is pairing energy (P)?

Answer 33

The energy needed to pair an electron in the same orbital

Question 34

When you get to d4, what do you use to determine where you put the 4th electron?

Answer 34

depends on the size of ΔO and the pairing energy (P)

Question 35

What are weak field ligands?

Answer 35

They have a small splitting energy ΔO | They are high spin

Question 36

Where is the more energetically favourable place to put the 4th electron for a weak field ligand?

Answer 36

In the higher energy level | to make it t2g3 eg1

Question 37

How do you increase the spin of an orbital?

Answer 37

Have all the electrons pointing up

Question 38

What are strong field ligands?

Answer 38

They have a large splitting energy ΔO | They are low spin

Question 39

How do you make an orbital low spin?

Answer 39

Pair up the electrons

Question 40

Where is the most favourable place to put the 4th electron for a strong field ligand?

Answer 40

in the lowest energy orbital paired up

Question 41

What does paramagnetic mean?

Answer 41

Unpaired electrons

Question 42

What does diamagnetic mean?

Answer 42

Paired electrons

Question 43

Where is tetrahedral filling of electrons likely to start?

Answer 43

At the bottom as ΔG will be small