Topic 13.2: Colored complexes

Question 1

Complex ion

Answer 1

Formed when ligands dative covalently bond to a central metal ion by donating a pair of electrons

Question 2

Substrative color mixing

Answer 2

a) Some of the wavelength components of white light are removed by absorption
b) Reflected light is deficient in some wavelength components, so it transmits the complementary color

Question 3

Why are the d-orbital electrons of central metal raised in a complex ion?

Answer 3

As ligand approaches the metal to form a complex ion the non-bonding pairs of electrons on the ligand will repel the d orbital causing the five d orbitals to split: 3 to lower energy and 2 to higher energ

Question 4

What is the name of the difference in energy between the two groups of d-obirtals?

Answer 4

Crystal field splitting

Question 5

Color of compounds of group 1, 2, and 3

Answer 5

White

Question 6

What does the formation of colored substances require?

Answer 6

Presence of a partially filled d subshell

Question 7

Why are complex ions of d-block elements colored?

Answer 7

a) The energy gap between the two levels corresponds to the wavelength of visible light
b) Electrons can transition from the lower to a higher set of d orbitals by absorbing certain wavelengths of light.
c) The complementary color of the color that is absorbed is transmitted

Question 8

Factors that affect the color of a transition metal

Answer 8

a) Identity of the metal ion
b) Oxidation number of the metal
c) Identity of the ligand

Question 9

Identity of the metal ion

Answer 9

Higher the nuclear charge, higher the split

a) A higher nuclear charge on the metal ion for the same number of electrons causes the ligands to be pulled in more closely, so that there is greater repulsion between the ligand electrons and the d electrons of the transition metal ion – and therefore greater splitting of the d orbitals
b) Different metal ions have different electron configurations and, because colors are caused by electron transitions, different arrangements of electrons give rise to different colors due to different amounts of repulsion between electrons.

Question 10

Oxidation nymber of the metal

Answer 10

A higher charge on the metal ion causes the ligands the ligands to be pulled in more closely, so that there is greater repulsion between the ligand electrons and the d electrons of the transition metal ion, and therefore greater splittiong of the d orbitals

Question 11

Identity of the ligand

Answer 11

The wavelength (energy) at which maximum absorbance occurs decreases (increases) with the charge density of the ligand, producing a larger split in the d orbitals

Question 12

Spectrochemical series

Answer 12

It arranges ligands in order of their ability to split d-orbitals in an octahedral complex ion