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Chemistry > Chapter 28 Transition Elements Part 2 > Flashcards

Chapter 28 Transition Elements Part 2 Flashcards

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1
Q

Principles of ligand exchange.

A
  • Weaker ligand will always be replaced by a stronger ligand. Forms a new complex that is more stable than the last.
  • Ligands in the original complex can be partially or entirely substituted by others.
  • No changes in coordination number, or the geometry of the complex, if the ligands are of a similar size.
  • If ligands are of a different size, e. g. water ligands and chloride ligands, then a change in coordination number & the geometry of the complex will occur.
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2
Q

Reaction of Cu2+ with conc. HCl
Observations?
What happens when H2O is added to the product?

A
  • [Cu(H2O)6]2+ + 4Cl- <> [CuCl4]2- + 6H2O
  • Pale blue solution to yellow solution.
  • Eq. shifts to LHS upon adding H2O, pale blue solution reforms.
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3
Q

Reaction of Co2+ with conc. HCl
Observations?
What happens when H2O is added to the product?

A
  • [Co(H2O)6]2+ + 4Cl- <> [CoCl4]2- + 6H2O
  • Pink solution to blue solution.
  • Eq. shifts to LHS upon adding H2O, pink solution reforms.
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4
Q

Reaction of Cu2+ with NaOH.
Observations?
Type of reaction?
What happens when H2O is added to product?

A
  • [Cu(H2O)6]2+ + OH- –> Cu(H2O)4(OH)2 (s) + 2 H2O
  • Pale blue solution to blue ppt
  • Acid-base reaction (NOT ligand exchange)
  • No change.
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5
Q

Reaction of Co2+ with NaOH.
Observations?
Type of reaction?
What happens when H2O is added to product?

A
  • [Co(H2O)6]2+ + OH- –> Co(H2O)4(OH)2 (s) + 2 H2O
  • Pink solution to blue ppt
  • Acid-base reaction (NOT ligand exchange)
  • No change.
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6
Q

What happens when Co(H2O)4(OH)2 undergoes oxidation? Why can’t it react further with OH-?

A
  • Brown ppt
  • Co(OH)3 forms
  • Turns to aqueous solution - Co(H2O)4(OH)2 (s) + 2 OH- –> [Co(H2O)3(OH)3]- (aq)
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7
Q

Reaction of Cu2+ with limited NH3.
Reaction of NH3 + H2O?
Observations?
Type of reaction?

A
  • Cu(H2O)6 2+ + 2OH- –> Cu(H2O)4(OH)2 (s) + 2H2O
  • NH3 + H2O –> NH4+ + OH-
  • Pale blue solution to blue ppt
  • Acid-base reaction
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8
Q

Reaction of Cu2+ with excess NH3.
Observations?
Type of reaction?

A
  • Cu(H2O)4(OH)2 (s) + 4NH3 (aq) –> Cu(NH3)4(H2O)2 2+ + 2H2O
  • Blue ppt to dark blue solution
  • Ligand exchange
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9
Q

Reaction of Co2+ with limited NH3.
Reaction of NH3 + H2O?
Observations?
Type of reaction?

A
  • Co(H2O)6 2+ + 2OH- –> Co(H2O)4(OH)2 (s) + 2H2O
  • NH3 + H2O –> NH4+ + OH-
  • Pink solution to blue ppt
  • Acid-base reaction
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10
Q

Reaction of Co2+ with excess NH3.
Observations?
Type of reaction?

A
  • Co(H2O)4(OH)2 (s) + 4NH3 (aq) –> Co(NH3)4(H2O)2 2+ + 2H2O
  • Blue ppt to brown solution
  • Ligand exchange
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11
Q

What do complexes with no charges form?

A

Ppt

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12
Q

Kstab.

A
  • equilibrium constant for the formation of the complex ion in a solvent from its constituent ions or molecules
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13
Q

Greater Kstab

A
  • equilibrium position more to the right
  • RHS complex more stable
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14
Q

Smaller Kstab

A
  • equilibrium position more to the left
  • LHS complex more stable
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15
Q

Geometrical isomerism

A

Complexes with the same molecular formula but different geometrical arrangements.

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16
Q

Angle between the same molecule/atom in cis

A

90°

17
Q

Angle between the same molecule/atom in trans

A

180°

18
Q

When does optical isomerism occur?

A

Molecules without plane of symmetry

19
Q

Types of square planar complexes

A
  • MA4
  • MA3B
  • MA2B2
  • MABCD
20
Q

Types of octahedral complexes

A
  • MA6
  • MA5B
  • MA4B2
  • MA3B3
  • M(A-A2)B2
  • M(A-A3)
21
Q

Types of ligands in M(A-A2)B2 & M(A-A3)

A
  • Bidentate.
  • Only complexes with bidentate ligands have optical isomers (most of the time).
22
Q

State if the following square planar complexes have geometrical or optical isomerism:
- MA4
- MA3B
- MA2B2
- MABCD

A
  • MA4 - no geo, no optic
  • MA3B - no geo, no optic
  • MA2B2 - has geo, no optic
  • MABCD - has geo, has optic
23
Q

State if the following octahedral complexes have geometrical or optical isomerism:
- MA6
- MA5B
- MA4B2
- MA3B3
- M(A-A2)B2
- M(A-A3)

A
  • MA6 - no geo, no optic
  • MA5B - no geo, no optic
  • MA4B2 - cis-trans, both no optical
  • MA3B3 - cis-trans - both no optical (because plane of symmetry when cut diagonally)
  • cis-M(A-A2)B2 - optical (think of the 2 types of propellers)
  • trans-M(A-A2)B2 - no optic
  • M(A-A3) - no geo, has optical (think of propellers)
24
Q

What type of repulsion do the different d-orbitals experience?

A

dx^2-y^2 & dz^2:
- on axes
- head-on repulsion

dxy, dxz, dyz:
- between axes

25
Q

Why are complexes coloured?

A
  • Ligands repel d-orbitals unequally.
  • d-orbitals split with energy gap.
  • Electrons from lower energy level absorbs white light & jumps to higher energy level.
  • Electrons returned to ground state & emit complementary light.
26
Q

Why do transition elements have different colours?

A
  • Stronger ligand (depends on the nature of the ligand).
  • Greater repulsion, greater energy gap.
  • Greater splitting.
  • More energy absorbed
27
Q

How to identify the colour?

A
  • Colour wheel

Chemistry (13 decks)

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