DM - Complex ions

Question 1

What are complex ions?

Answer 1

Metal ions surrounded by ligands.

Question 2

What is a complex (complex ion)?

Answer 2

A central metal atom or ion surrounded by coordinately bonded ligands.

Question 3

What is a coordinate bond?

Answer 3

A dative covalent bond.

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

Question 4

Where do both electrons come from in a coordinate bond in a complex?

Answer 4

The ligands.

Question 5

What is a ligand?

Answer 5

An atom, ion or molecule that donates a pair of electrons to a central transition metal ion to form a coordinate (dative covalent) bond.

Question 6

How do ligands form bonds?

Answer 6

Using lone pairs of electrons.

Question 7

What must a ligand have to be able to bond?

Answer 7

At least one lone pair of electrons, or it won’t have anything to form a coordinate bond with.

Question 8

What are ligands with one lone pair called?

Answer 8

Monodentate (or unidentate).

Question 9

What are monodentate (or unidentate) ligands?

Answer 9

Ligands with one lone pair.

Question 10

What are ligands with two lone pairs called?

Answer 10

Bidentate.

Question 11

What are bidentate ligands?

Answer 11

Ligands with two lone pairs.

Question 12

What can bidentate ligands do?

Answer 12

Can each form two coordinate bonds with a metal ion.

Question 13

What are ligands with more than two lone pairs called?

Answer 13

Polydentate.

Question 14

What are polydentate ligands?

Answer 14

Ligands with more than one lone pair.

Question 15

Examples of monodentate/unidentate ligands

Answer 15

H2O (lone pair of e- on oxygen)

NH3 (lone pair on N)

Cl- (lone pair on Cl)

CN- (lone pair on C)

Question 16

Examples of bidentate ligands

Answer 16

Ethanedioate (lone pairs on O’s)

Ethylenediamine (lone pair on N’s)

Question 17

What is the bidentate ligand ethylenediamine often abbreviated to?

Answer 17

‘en’

Question 18

Examples of polydentate ligands

Answer 18

EDTA^4- (6 lone pairs so it’s a hexadentate - can form 6 coordinate bonds with a metal ion).

Question 19

What is the coordination number?

Answer 19

The number of coordinate (dative) bonds that are formed with the central metal ion.

Question 20

What are the usual coordination numbers?

Answer 20

6 and 4.

Question 21

What is the coordination number likely to be if the ligand is small - e.g. H2O or NH3?

Answer 21

6 - as 6 can fit around the central metal ion.

Question 22

What is the coordination number likely to be if the ligand is larger - e.g. Cl-?

Answer 22

4 - as only 4 can fit around the central metal ion.

Question 23

What shape does 6 coordinate bonds mean?

• Bond angles???

Answer 23

Octahedral.

90 degree bond angles.

Question 24

What shape does 4 coordinate bonds usually mean?

• Bond angles???

Answer 24

Tetrahedral.
109.5 degree bond angles.

But occasionally:
Square planar.
90 degree bond angles.