Chapter 4: 4.2 Crystal Field Theory (CFT)

Question 1

What assumptions are made in CFT?

Answer 1

Transition metal ion is a free metal ion by itself
Ligands are point charges
Bond between metal and ligand is totally electrostatic (ionic)

Question 2

True or False:
In a free metal ion, the five d orbitals of the same principal quantum number are degenerate

Answer 2

True, they have the same energies

Question 3

True or False:
Degeneracy applies to octahedral complexes

Answer 3

False, degeneracy is broken in octahedral complexes

Question 4

What two d orbitals experience destabilization? Why?

Answer 4

dz2 and dx2-y2
The lobes point directly at the ligands, increasing repulsion

Question 5

The energy separation between the destabilized orbitals and the stabilized orbitals is known as what?

Answer 5

Crystal Field

Question 6

Define:
Barycenter

Answer 6

The total energy of the five d orbital remains unchanged with respect to their energy in a spherical field

Question 7

What factors affect crystal field splitting?

Answer 7

Oxidation state of the metal ion
Identity of the metal
Nature of the ligand

Question 8

How does oxidation state of the metal ion affect crystal field splitting?

Answer 8

Increases with increasing oxidation state of the metal because the greater charge on the metal increases the electrostatic metal-ligand interaction energy

Question 9

How does identity of the metal affect crystal field splitting?

Answer 9

Increases going down a group due to expansion of the metal’s d orbitals which increases the metal-ligand interaction

Question 10

What is the phenomenon of complementary colours?

Answer 10

If a solution of a complex absorbs visible light one color, our eyes will see the complementary color

Question 11

List the color of light absorbed and the color we see

Answer 11

Green (Red)
Yellow (Purple)
Orange (Blue)

Question 12

What does absorbing a shorter wavelength of light mean?

Answer 12

The greater the value of d orbital energy splitting

Question 13

The less the value of d orbital splitting, the ______ the wavelength of light is absorbed

Answer 13

Longer

Question 14

What technique is used to measure colors and color intensities absorbed by a chemical compound dissolved in solution?

Answer 14

Ultraviolet-visible absorption spectroscopy

Question 15

What instrument is used in UV-vis spectrocscopy?

Answer 15

UV-vis spectrometer

Question 16

Describe high-spin configuration

Answer 16

The configuration with the more unpaired electrons

Question 17

Describe low-spin configuration

Answer 17

The configuration with the more paired electrons

Question 18

Should one put the electrons in the high energy orbitals?

Answer 18

Depends
Higher energy orbitals will be less stable
Forcing electrons into already occupied orbitals will also decrease stability

Question 19

Define:
Pairing energy

Answer 19

Energy required to overcome the repulsive interaction between the two electrons occupying the same orbital