Transition Metals: Complex Ions and Colour

Question 1

What is the definition of a complex ion?

Answer 1

A complex ion is a metal ion surrounded by dative covalently bonded ligands.

Question 2

What is a dative covalent bond (or coordinate bond)?

Answer 2

A covalent bond in which both electrons in the shared pair come from the same atom.

Question 3

What is a ligand?

Answer 3

An atom, ion or molecule that donates a pair of electrons to a central metal ion.

Question 4

What is the coordination number?

Answer 4

The number of dative covalent bonds that are formed with the central metal ion.

Question 5

When will the coordination number typically be 6?

Answer 5

When the ligands are small (e.g. H₂O, CN^-, NH₃).

Question 6

What is ligand substitution? Also, what does it usually cause?

Answer 6

When one ligand is swapped with another. It usually causes a colour change.

Question 7

What is an example of a larger ligand, of which only 4 can fit around the central metal ion?

Answer 7

Cl^-.

Question 8

If there are 6 dative covalent bonds, what shape will it be?

Answer 8

Octahedral.

Question 9

If the shape of a complex ion is **tetrahedral (usual) **or square planar (rare), how many dative covalent bonds will it have?

Answer 9

4.

Question 10

If there are 2 dative covalent bonds, what shape will it be?

Answer 10

Linear.

Question 11

How do you work out the oxidation state of the metal?

Answer 11

Oxidation state of the metal ion = total oxidation state - sum of the oxidation states of the ligands.

Question 12

What does it mean when a ligand is monodentate (or unidentate) / bidentate / polydentate?

Answer 12

The ligand has 1 / 2 / many lone pairs respectively.

Question 13

How many dative covalent bonds does Haemoglobin form, and with what?

Answer 13

4, 1 per Nitrogen. Each forms a fond with Fe²⁺.

Question 14

How many lone pairs does EDTA^4- have?

Answer 14

6, (therefore hexadentate).

Question 15

How is colour created in transition metals when ligands are involved?

Answer 15

1. Normally, all 3d orbitals have the same energy.
2. In a complex, repulsion occurs between the electrons in the ligands and the 3d electrons in the metal, increasing the energy of all the 3d orbitals.
3. Some are increased more than others, therefore the 3d orbitals are split into two different energy levels.
4. Electrons typically occupy lower orbitals, but can jump up to the higher orbitals by absorbing light energy equal to the energy gap.

Question 16

What happens to light frequencies that aren’t absorbed by a complex transition metal ion? Also, what’s the name for these colours?

Answer 16

They are transmitted. The complement colour to the absorbed colour.

Question 17

What factors can affect the size of the energy gap? What visible property can this change?

Answer 17

1. Changes in oxidation state.
2. Changes in coordination number.
3. Changes in ligand.

Can change the colour.