A-level Chemistry > 5.5 - Transition elements > Flashcards

5.5 - Transition elements Flashcards

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1
Q

Define ‘d-block’ elements ?

A

They are elements whose highest energy electrons occupy a d-orbital/ sub shell

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2
Q

Define ‘Transition elements’ ?

A

Transition elements : Elements with an incomplete d-subshell that can form at least one stable ion with an incomplete d-subshell

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3
Q

What metals do not fit the definition of a transition metal ?

A
  • Zinc
  • Scandium
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4
Q

Explain why zinc and scandium are not considered as transition metals ?

A
  • Scandium only forms Sc^3+ ions, configuration [Ar] 3d^0
  • The d-subshell is completely empty
  • Zinc only forms the ion Zn^2+, configuration [Ar] 3d^10
  • The d-subshell is completely filled
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5
Q

What are the two exceptions to the Aufbau Principle ?

A
  • Copper
  • Chromium
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6
Q

Explain how copper and chromium are two exceptions to the Aufbau Principle ?

A
  • Cr is [Ar] 3^d5 4s^1 not [Ar] 3d^4 4s^2
  • Cu is [Ar] 3d^10 4s^1 not [Ar] 3d^9 4s^2
  • These configurations are energetically more stable
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7
Q

What are the properties of transition elements ?

A
  • Variable oxidation states
  • Form complex ions
  • Form coloured compounds
  • Behave as catalysts
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8
Q

What is a complex ?

A

A molecule or ion containing a central metal atom or ion, with a number of molecules or ions/ ligands surrounding it

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9
Q

Define ‘Ligand’ ?

A

Ligand : A species that forms a coordinate bond with a central metal ion by donating a lone pair of electrons to metal ion

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10
Q

Explain how transition elements act as catalysts ?

A
  • Transition elements are good catalysts since they have variable oxidation states
  • During catalysis, the transition element can change to various oxidation states by gaining electrons or donating electrons from reagents within the reaction
  • Substances can also be adsorbed onto their surface and activated
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11
Q

What are the two types of catalysts ?

A
  • Homogenous catalyst
  • Heterogenous catalyst
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12
Q

What is a homogenous and heterogenous catalyst ?

A
  • A heterogeneous catalyst is a catalyst that has a different physical state (phase) as the reactants
  • A homogenous catalyst is a catalyst that has the same physical state ( phase ) as the reactants
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13
Q

Define ‘co-ordination number’ ?

A

Co-ordination number : The number of co-ordinate bonds to the central metal ion

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14
Q

What are Monodentate Ligands ?

A

Monodentate ligand : A species that contains one lone pair of electrons and forms one coordinate bond to a central metal ion BY DONATING A LONE PAIR OF ELECTRONS to the central metal ion

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15
Q

Name examples of Monodentate Ligands ?

A
  • Water (H2O) molecules
  • Ammonia (NH3) molecules
  • Chloride (Cl–) ions
  • Cyanide (CN–) ions
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16
Q

What are bidentate ligands ?

A

Bidentate ligands : A species contains two lone pair of electrons and forms two coordinate bonds with the central metal ion BY DONATING TWO LONE PAIRS OF ELECTRONS to the central metal ion

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17
Q

Name examples of bidentate ligands ?

A
  • 1,2-diaminoethane (Hv2NCHv2CHv2NHv2) / ‘en’
  • Ethanedioate ion (Cv2Ov4^2- )/ ‘ox’
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18
Q

What does the geometry of transition element complexes depend on ?

A
  • Size of ligands
  • Number of dative bonds to the central metal ion
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19
Q

What are the different geometrical complexes of transition element complexes ?

A
  • Six-coordinate complexes ( Octahedral )
  • Four-coordinate complexes ( Tetrahedral or square planar )
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20
Q

What is the coordinate number and bond angle of octahedral complex ?

A
  • Coordinate number = six
  • Consist of six mono dentate ligands or three bidentate ligands or a mixture of both
  • Bond angle = 90o
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21
Q

What is the coordinate number and bond angle of tetrahedral complex ?

A
  • Coordinate number = four
  • Typically complexes contain four Cl- ligands
  • Bond angle = 109.5o
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22
Q

What is the coordinate number and bond angle of square planar complex ?

A
  • Coordinate number = four
  • Typically complexes contain four CN- ligands
  • Bond angle = 90o
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23
Q

What transition element complexes exhibit geometrical cis-trans isomerism ?

A
  • Square planar and octahedral complexes - They have two ligands attached to it that are different to the rest
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24
Q

Explain how to identify cis-trans geometrical isomerism in transition element complexes ?

A
  • If the two ligands are next to each other then that is the ‘cis’ isomer
  • If the two ligands are opposite each other then this is the ‘trans’ isomer
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25
Draw optical isomers of complex [Ni(Hv2NCHv2CHv2NHv2)v3]^2 ?
26
Draw cis-platin and trans-platin ?
27
What are the uses of cis-platin ?
Cis-platin is an extremely effective cancer drug that prevents DNA replication
28
How does cis-platin function ?
- Cis-platin passes through the cell membrane - It undergoes ligand substitution where the chloride ligands are replaced by water ligands - Nitrogen atoms ( of guanine bases ) is a better ligand than water and forms coordinate bonds with the cis-platin - Cis-platin distorts the shape of the DNA and prevents the DNA from replicating
29
What are the adverse effects of cis-platin ?
- Cis-platin binds to healthy cells and cancerous cells - Cancer cells are more affected since they replicate faster - However, this means healthy cells which replicate quickly are also affected by cis-platin
30
What is Ligand substitution ?
Ligand substitution : When one ligand replaces another
31
What does ligand substitution depend on ?
Size of ligands
32
Explain how size of ligand affected ligand substitution ?
- Similar size = no changes to Coordination number and Geometry of the complex - Different size = changes to the Coordination number and Geometry of the complex
33
What are the three substation reactions with copper (ll) complexes ?
- Sodium hydroxide solution, NaOH (aq) - Ammonia solution, NHv3 (aq) - Hydrochloric acid, HCl (aq)
34
What are the colours of copper hexaaqua complex [Cu(Hv2O)v6]^2+ ?
Pale blue solution
35
Explain NaOH substitution of copper(II) complexes ?
- Addition of NaOH solution = light blue precipitate - Partial ligand substitution = two water ligands are replaced by two hydroxide ligands
36
Explain addition excess NaOH of copper(II) complexes ?
No change
37
Explain NHv3 substitution of copper(II) complexes ?
- Addition of NHv3 solution = light blue precipitate - Partial ligand substitution : two water ligands are replaced by two hydroxide ligands
38
Explain addition of excess NHv3 of copper(II) complexes ?
- Addition of excess NHv3 = Dark blue solution - Partial ligand substitution : two water ligands and two hydroxide ligands are replaced by four ammonia ligands
39
Explain HCl substitution of copper (ll) complexes ?
- Full ligand substitution : all water ligands are replaced by four chloride ligands - Octahedral geometry changes to tetrahedral geometry - Pale blue solution changes to yellow solution
40
What are the two types of substitutions in chromium(III) complexes ?
- Sodium hydroxide solution, NaOH (aq) - Ammonia solution, NHv3 (aq)
41
What is the colour of chromium hexaaqua complexes [Cr(Hv2O)v6]^3+ ?
Pale purple solution
42
Explain NaOH substitution of chromium(III) complexes ?
- Addition of NaOH solution = dark green precipitate - Partial ligand substitution = Three water ligands are replaced by three hydroxide ligands
43
Explain addition excess NaOH of chromium(III) complexes ?
- Excess NaOH solution = Dark green solution - Full ligand substitution occurs = 3 remaining water ligands are replaced by three hydroxide ligands
44
Explain NH3 substitution of chromium(III) complexes ?
- Addition of NHv3 solution = dark green precipitate - Partial ligand substitution = Three water ligands are replaced by three hydroxide ligands
45
Explain addition of excess NH3 of chromium(III) complexes ?
- Excess NHv3 solution = purple solution - Full ligand substitution = all the water ligands are replaced by six ammonia ligands
46
What are the different aqueous transition metal ions with sodium hydroxide ?
47
What are the different aqueous transition metal ions with ammonia ?
48
Explain ligand substitution in haemoglobin ?
- The haem molecule is a complex with iron(II) at its centre - Oxygen forms a coordinate bond/ bonds to Fe2+ ion - Ov2 binds reversibly with Fe2+ ion and is replaced by Hv2O or COv2
49
Explain the effect of carbon monoxide in haemoglobin ?
- CO binds/ bonds more strongly with Fe2+ ion than Ov2 - This prevents Ov2 from binding to Fe2+ and being carried/ transported to the cells
50
What are the different tests for anions ?
- Testing for COv3^2- ions - Testing for SOv4^2- - Testing for halide ions
51
What are the different tests for cations ?
- Adding aqueous NaOH solution to precipitate Cr^2+, Fe^2+, Fe^3+, Mn^2+, Cu^2+ - Testing for NHv4+ ions
52
Explain how to prepare solid mixture to test for the presence of various ions ( (NH4)2Fe(SO4)2*xH2O, which is soluble in water, unlike limestone / CaCOv3 ) ?
- Sample is dissolved in and stirred with water - Mixture is filtered - Test for presence of SO42−, Fe2+, NH4+ on filtrate - Test for COv3^2- ions on remaining residue/ solid
53
Name examples of reducing and oxidising agents used during redox reactions with transition metals ?
- Reducing agents : KI/ I- and Zn/ H+ - Oxidising agents : H+ / MnOv4- and Hv2Ov2 and Clv2 and Crv2Ov7^2- / H+
54
What are the different redox reactions with iron ions ?
- Oxidation of Fe2+ to Fe3+ - Reduction of Fe3+ to Fe2+
55
Explain oxidation of Fe2+ to Fe3+ ?
- MnOv4- is used as oxidising agent to oxidise Fe2+ to Fe3+ ions - Purple solution turns colourless
56
Explain reduction of Fe3+ to Fe2+
- ( KI ) I- is oxidised to Iv2 and is reducing agent - Fe3+ ions are reduced to Fe2+ ions - Orange-brown solution turns pale-green brown
57
What are the different redox reactions with chromium and dichromate ions ?
- Reduction of Crv2Ov7^2- to Cr3+ ions - Reduction of Cr3+ ions to Cr2+ ions - Oxidation of Cr3+ ions to CrOv4^2- ions - Oxidation of CrOv4^2- ions to Crv2Ov7^2- ions
58
Explain reduction of Crv2Ov7^2- to Cr3+ ions ?
- Zinc is oxidised to Zn2+, it is a reducing agent - Crv2Ov7^2- are reduced to Cr3+ ions - Orange solution turns green
59
Explain reduction of Cr3+ ions to Cr2+ ions ?
- EXCESS ZINC is oxidised to Zn2+, it is a reducing agent - Cr3+ ions are reduced to Cr2+ - Green solution turns pale blue
60
Explain oxidation of Cr3+ ions to CrOv4^2- ions ?
- Hot alkali hydrogen peroxide is an oxidising agent - Cr3+ ions are oxidised to CrOv4^2- ions - Dark green solution turns yellow
61
Explain oxidation of CrOv4^2- ions to Crv2Ov7^2- ions ?
- Dilute sulphuric acid is added - CrOv4- ions are oxidised to Crv2Ov7^2- ions - Yellow solution turns orange
62
What are the different redox reactions with copper ions ?
- Reduction fo Cu2+ ions to Cu+ ions - Disproportion of Cu+ ions
63
Explain reduction of Cu2+ ions to Cu+ ions ?
- ( KI ) I- is oxidised to Iv2 and is reducing agent - Cu2+ ions are reduced to Cu+ ions - Pale blue solution forms white precipitate - Iodine is brown
64
Explain disproportion of Cu+ ions ?
- Cuv2O reacts with dilute sulphuric acid - Cu+ ions are both oxidise and reduced - Brown precipitate of Cu is formed and blue solution of Cu(SOv4)
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