24.2 Formation of Complex Ions

Question 1

How are complex ions formed?

Answer 1

1 or more ligands

form dative covalent bond

with central metal ion

Question 2

What is a ligand?

Answer 2

ion/molecule

which donates electron pair

to central metal ion

forming dative covalent bond

Question 3

What is a dative covalent bond?

Answer 3

Bond formed when

1 atom in bond

provides both electrons in shared pair

Question 4

What is a coordination number?

Answer 4

Indicates number of dative covalent bonds

attached to central metal ion

Question 5

What is a monodentate ligand?

Answer 5

A ligand

which can only (donate 1 electron pair / form 1 dative covalent bond)

with central metal ion

Question 6

What is a bidentate ligand?

Answer 6

A ligand

which can (donate 2 electron pairs / form 2 dative covalent bonds)

with central metal ion

Question 7

What are common monodentate ligands?

Answer 7

• WATER - H2O:
• AMMONIA - :NH3
• CHLORIDE - :Cl^-
• CYANIDE - :CN^-
• HYDROXIDE - :OH^-

Question 8

What are common bidentate ligands?

Answer 8

• 1,2 DIAMINOETHANE (en)
• ETHANEDIOATE

Question 9

Draw the structural formula of a 1,2diaminoethane molecule:

Answer 9

Question 10

Draw the structural formula of an ethanedioate molecule:

Answer 10

Question 11

State the formula, shape, & bond angle of this complex ion:

Answer 11

[Cr(H₂O)₆]³⁺

octahedral, 90°

Question 12

State the formula, shape, & bond angle of this complex ion:

Answer 12

[Co(Cl)₄]^2-

tetrahedral, 109.5°

Question 13

State the formula, shape, & bond angle of this complex ion:

Answer 13

[Co(NH₂)₄]²⁺

square planar, 90

Question 14

Each water molecule has 2 lone pairs on the oxygen atom. Why is it not a bidentate ion?

Answer 14

a single oxygen atom cannot utilise both lone pairs to form 2 dative covalent bonds with the central metal ion

because other lone pair would be facing the opposite direction to the central metal ion

Question 15

What is the chemical formula of a cyanide ion?

Answer 15

:CN^-

Question 16

What is the chemical formula of a diaminoethane ion?

Answer 16

H₂CH₂CH₂NH₂

Question 17

What is the chemical formula of an ethanedioate ion?

Answer 17

(COO^-)₂

Question 18

Rank the ligands H₂O:, :Cl^- & :NH₃ in terms of their strength as ligands.

Answer 18

(strongest)

:Cl^-

:NH₃

H₂O:

(weakest)

Question 19

Describe & explain the differences in strength of H₂O:, :Cl^- & :NH₃ as ligands.

Answer 19

H₂O is weakest, ∴ displaced by both

• O has high electronegativity, so greater attraction of lone pair.
  
  • Does not give up lone pair to form dative covalent bond as easily.

NH3 is neither weakest nor strongest, ∴ displaces H₂O & displaced by Cl^-

• N is less electronegative than O, so weaker attraction of lone pair to N.
  
  • Gives up lone pair more easily to form dative covalent bond.

Cl^- is strongest, ∴ displaces both.

• negative charge, so repels lone pair.
  
  • gives up lone pair much more easily, forming dative covalent bond.

Question 20

Why can 6 H₂O bond to a central metal ion whereas only 4 Cl^- can do the same?

Answer 20

Cl ions are much bigger than H₂O,

so only 4 Cl can fit as opposed to 6 H₂O.