5.3.3: Transition metals and complex ions

Question 1

What is a complex ion?

Answer 1

A transition metal ion bound to one or more ligands by coordinate bonds (dative covalent bonds).

Question 2

What are ligands?

Answer 2

A ligand is a molecule or ion that can donate a pair of electrons to the transition metal ion to form a coordinate bond.

Question 3

What is the coordination number?

Answer 3

The total number of coordinate bonds formed between a central metal ion and its ligands

Question 4

What is a coordinate bond?

Answer 4

• A bond in which one of the atoms provides both electrons for the covalent bond.
• The transition metal ion accepts the pair of electrons from the ligand in forming the coordinate bond.

Question 5

How are ligands Lewis bases?

Answer 5

They are electron donors.

Question 6

How is [Cu(H2O)6]2+ an example of a complex ion?

Answer 6

• The central metal ion is Cu2+
• The ligands are molecules of water, H2O.
• Each water molecule donates a lone pair of electrons from its oxygen atom to the Cu2+ ion to form a coordinate bond.
• Coordinate number=6

Question 7

What is the overall charge of a complex ion?

Answer 7

The sum of the individual charges of the transition metal ion and those of the ligands present in the complex.

Question 8

When is a ligand monodendate?

Answer 8

In a monodendate ligand, the ligand donates just one pair of electrons to the central metal ion to form one coordinate bond.

Question 9

When is a ligand bidendate?

Answer 9

• Bindendate ligands have two pairs of electrons from different atoms to donate to the central metal.
• This means two coordinate bonds can be formed.

Question 10

What is The most common bidendate ligand?

Answer 10

ethane-1,2-diamine (NH2CH2CH2NH2) ‘en’.

-Each nitrogen atom donates its lone pair to the metal ion.

Question 11

Name of ligand:
Water
What is the formula and charge?

Answer 11

:OH2

none-neutral ligand

Question 12

Name of ligand:
Ammonia
What is the formula and charge?

Answer 12

:NH3

none-neutral charge

Question 13

Name of ligand:
Thiocyanate
What is the formula and charge?

Answer 13

:SCN-

-1 charge

Question 14

Name of ligand:
Cyanide
What is the formula and charge?

Answer 14

:CN-

-1 charge

Question 15

Name of ligand:
Chloride
What is the formula and charge?

Answer 15

:Cl-

-1 charge

Question 16

Name of ligand:
hydroxide
What is the formula and charge?

Answer 16

:OH-

-1 charge

Question 17

What is a hexadentate ligand?

Answer 17

A ligand that has 6 lone pairs of electrons available to form coordinate bonds.

Question 18

What is one example of a hexadentate ligand?

Answer 18

Ethylenediaminetetraacetic acid (EDTA)
-Exists in complexes as the ion EDTA4-

Question 19

What is EDTA used for and what is it?

Answer 19

• To bind metal ions.
• It is known as a chelating agent.
• This means that EDTA decreases the conc. of metal ions in solutions by binding them into a complex.

Question 20

How is EDTA used in detergents?

Answer 20

-It binds to calcium and magnesium ions to reduce hardness in water.

Question 21

How is EDTA used in foods?

Answer 21

-As a stabiliser to remove metal ions that might catalyse the oxidation of the product.

Question 22

How is EDTA used in medical applications?

Answer 22

-It is added to blood samples to prevent clotting and used to treat patients suffering from lead and mercury poisoning.

Question 23

Describe the features of an octahedral complex.

• No. of coordinate bonds
• shape
• bond angles

Answer 23

• Six-coordinate bonds attached to the central ion.
• The outer face of the shape is an eight-sided octahedron.
• Four of the ligands are in the same plane, one ligand is above the plane and the remaining ligand is below the plane.
• All bond angles are 90 or 180.

Question 24

What shape do chloride complexes form and why?

Answer 24

• Tetrahedral shape

- Chloride ligands are so large that only four can fit around a transition metal ion.

Question 25

What is another rare four ligand structure?

Answer 25

• A square planar complex.
• This is when the for monodentate ligands arrange themselves in the same plane as the metal ion.
• e.g. Cis-platain.