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CHY1301 - Fundamentals of inorganic chemistry > Crystal field theory > Flashcards

Crystal field theory Flashcards

1
Q

What does the crystal field theory assume?

A

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

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2
Q

What phase is it assumed the metal is in?

A

Gas phase

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3
Q

Where are the negatively charged ligands assumed to be from?

A

infinity

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4
Q

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

A

5

They have the same energy - degenerate

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5
Q

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

A

2
dz²
dx²-y²

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6
Q

What is the high energy level called for octahedral complexes?

A

eg

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7
Q

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

A

3
dxy
dyz
dxz

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8
Q

What is the low energy level called for octahedral complexes?

A

t2g

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9
Q

What is the gap between eg and t2g called?

A

ΔO (oct)

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10
Q

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

A

+3/5 ΔO

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11
Q

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

A

-2/5 ΔO

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12
Q

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

A

The electrons in the d-orbitals start to sense them

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13
Q

Why do dz² and dx²-y² rise in energy?

A

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

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14
Q

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

A

They point in between the axes and are lower in energy

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15
Q

In a tetrahedral complex, where do the ligands point?

A

In between the axes

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16
Q

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

A

dxy
dyz
dxz

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17
Q

In an octahedral complex, where do the ligands point?

A

dz² and dx²-y² point along the xyz axes

dxz, dyz and dxy point in between the axes

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18
Q

In a tetrahedral complex, which orbitals are high energy?

A

dxy
dyz
dxz

19
Q

In a tetrahedral complex, which orbitals are low energy?

A

dz² and dx²-y²

20
Q

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

A

t2

21
Q

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

A

e

22
Q

Why are the labels for octahedral and tetrahedral complexes different?

A

There is no symmetry in tetrahedral molecules

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

23
Q

What is the difference in energy between t2 and e?

A

Δtet

24
Q

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

A

+2/5Δt

25
Q

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

A

-3/5Δt

26
Q

How does the splitting term for Δtet compare to Δoct?

A

Smaller

27
Q

What is a tetragonal distortion?

A

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

28
Q

What does tetragonal distortion remove?

A

the degeneracy of eg

29
Q

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

A

The d-orbitals with a z component lower in energy

30
Q

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

A

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

31
Q

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

A

Eventually the two ligands are removed to infinity

32
Q

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

A

From the bottom

t2g

33
Q

What is pairing energy (P)?

A

The energy needed to pair an electron in the same orbital

34
Q

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

A

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

35
Q

What are weak field ligands?

A

They have a small splitting energy ΔO

They are high spin

36
Q

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

A

In the higher energy level

to make it t2g3 eg1

37
Q

How do you increase the spin of an orbital?

A

Have all the electrons pointing up

38
Q

What are strong field ligands?

A

They have a large splitting energy ΔO

They are low spin

39
Q

How do you make an orbital low spin?

A

Pair up the electrons

40
Q

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

A

in the lowest energy orbital paired up

41
Q

What does paramagnetic mean?

A

Unpaired electrons

42
Q

What does diamagnetic mean?

A

Paired electrons

43
Q

Where is tetrahedral filling of electrons likely to start?

A

At the bottom as ΔG will be small

CHY1301 - Fundamentals of inorganic chemistry (36 decks)

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