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A-Level Chemistry > 24 Transition elements > Flashcards

24 Transition elements Flashcards

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1
Q

What are d-block elements?

A

The elements located between Group 2 and Group 13.

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2
Q

What are the properties of d-block elements?

A

They’re all metallic so:

  • High melting and boiling points
  • Shiny in appearance
  • Conduct both electricity and heat
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3
Q

What are some common uses of d-block elements?

A
  • Copper,silver,nickel,zinc in Coinage
  • Iron in Construction and production of tools
  • Copper in electrical cables and water pipes
  • Titanium in aerospace industry, joint replacement and cosmetic dentistry
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4
Q

Why do chromium and copper not follow the expected principle?

A
  • For stability
  • It’s believed that a half filled d5 subshell and a fully filled d10 subshell gives additional stability to atoms of chromium and copper.
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5
Q

What is the configuration of chromium?

A

3d5 4s1

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6
Q

What is the configuration of copper?

A

3d10 4s1

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7
Q

When forming an atom…

A

the 4s orbital fills before the 3d orbitals

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8
Q

When forming an ion…

A

the 4s orbital empties before the 3d orbitals.

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9
Q

What are transition elements defined as?

A

D-block elements that form at least one ion with a partially filled d-orbital.

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10
Q

How does scandium form the ion Sc3+ ?

A

By the loss of two 4s electrons and one 3d electron.

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11
Q

How does zinc form the ion Zn2+ ?

A

By the loss of its two 4s electrons.

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12
Q

Why are Sc3+ and Zn2+ ions not classified as transition elements?

A
  • Scandium only forms the ion Sc3+ by loss of two 4s electrons and one 3d electron.
  • Therefore Sc3+ ions have empty d-orbitals
  • Zinc forms the ion Zn2+ by the loss of two 4s electrons.
  • Therefore Zn2+ ions have full d-orbitals
  • So scandium and zinc do not form ions with partially filled d-orbitals and are not classified as transition elements.
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13
Q

What characteristics do transition elements have?

A
  • They form compounds in which the transition element has different oxidation states.
  • They form coloured compounds.
  • The elements and their compounds can act as catalysts.
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14
Q

What makes a strong oxidising agent?

A

A species containing a transition element in its highest oxidation state.

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15
Q

What are the colours of some transition elements?

A
  • Potassium dichromate (VI) : bright orange
  • Cobalt (II) chloride: Pink-purple
  • Nickel (II) sulfate: Green
  • Hydrated copper (II) sulfate: Blue
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16
Q

What is the colour of a solution linked to?

A

The partially filled d-orbitals of the transition metal ion.

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17
Q

Iron forms two common oxidation states +2 and +3. What are the colours of the solutions?

A
  • Iron (II): Pale green

- Iron (III): Yellow

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18
Q

Chromium forms two common oxidation states +3 and +6. What are the colours of the solutions?

A
  • Cr (III): Green

- Cr (VI): Yellow/Orange

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19
Q

In which process is an iron catalyst used?

A
  • The Haber process.

- For the manufacture of ammonia from the reaction between nitrogen and hydrogen.

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20
Q

In which process is a vanadium oxide catalyst used?

A
  • The Contact process.

- For the production of sulfur trioxide from the oxidation of sulfur dioxide.

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21
Q

What are these catalysts an example of?

A

Heterogenous catalysts as the catalyst is in a different physical state to the reactants.

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22
Q

What is a complex ion?

A

A transition metal ion bonded to ligands by coordinate bonds

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23
Q

What is a ligand?

A

A molecule or ion that donates a pair of electrons to a central metal ion to form a coordinate bond or dative covalent bond.

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24
Q

What is the coordination number?

A

It indicates the number of coordinate bonds attached to the central metal ion.

25
Q

What is a monodentate ligand?

A

A ligand that is able to donate one pair of electrons to a central metal ion.

26
Q

What is a bidentate ligand?

A

A ligand that can donate two lone pairs of electrons to the central metal ion, forming two coordinate bonds
E.g ethanedioate ion, 1,2-diaminoethane

27
Q

What shapes do six-coordinate complexes have?

A

Octahedral shape, bond angle= 90

28
Q

What shapes do four coordinate complexes have?

A

Tetrahedral, bond angle= 109.5

Square planar, bond angle= 90

29
Q

Examples of tetrahedral complexes

A

[CoCl4]2-

[CuCl4]2-

30
Q

Example of square planar complexes

A

[Pt(NH3)4]2+

31
Q

Which complex ions show cis-trans isomerism?

A

Four-coordinate & six-coordinates (Square planar and octahedral)
2 different monodentate ligands

32
Q

Which complex ions show optical isomerism?

A

Octahedral complexes containing two or more bidentate ligands

33
Q

Example of cis-trans isomerism in square planar complexes

A

[Pd(NH3)2Cl2]
Cis: 90 degrees apart
Trans: 180 degrees apart

34
Q

Example of cis-trans isomerism in octahedral complexes

A

MONODENTATE LIGANDS: [Co(NH3)4Cl2]+
BIDENTATE LIGANDS: 1,2-diaminoethane
[Co(NH2CH2CH2NH2)2Cl2]

35
Q

What are optical isomers?

A

Stereoisomers that are non-superimposable images of each other, also called ‘enantiomers’

36
Q

What is a ligand substitution reaction?

A

A reaction in which one or more ligands in a complex ion are replaced by different ions.

37
Q

What is the colour change when an excess of AQUEOUS AMMONIA is added to a solution containing [Cu(H2O)6]2+ ?

A

PALE BLUE-> DARK BLUE

38
Q

How many ammonia ligands replace the water ligands? & the equation of ligand substitution with ammonia

A

FOUR AMMONIA ligands replace FOUR OF THE WATER ligands
[Cu(H2O)6]2+ (aq) + 4NH3 (aq) -> [Cu(NH3)4(H2O)2]2+ (aq) + 4H2O (l)
Both are OCTAHEDRAL COMPLEXES

39
Q

What is formed in the first stage of ligand substitution with ammonia? [Cu(H2O)6]2+

A

A pale blue precipitate of Cu(OH)2 is formed

40
Q

What happens in the second stage of ligand substitution with ammonia? [Cu(H2O)6]2+

A

The Cu(OH)2 precipitate then dissolves in the excess ammonia to form a dark blue solution

41
Q

What is the colour change when an excess of CONC. HYDROCHLORIC ACID is added to a solution containing [Cu(H2O)6]2+ ?

A

PALE BLUE -> YELLOW SOLUTION

42
Q

How many chloride ligands replace the water ligands? & the equation of ligand substitution with HCL

A

FOUR chloride ligands replace the six water ligands. This is because chloride ligands are larger in size, so fewer can fit around the central Cu2+ ion.
[Cu(H2O)6]2+ (aq) + 4Cl- (aq) -> [CuCl4]2- (aq) + 6H2O (l)
[CuCl4]2- has a TETRAHEDRAL SHAPE

43
Q

What forms when chromium (III) potassium sulfate, KCr(SO4)2.12(H2O) dissolves in water?

A

The complex ion [Cr(H2O)6]3+ is formed.

44
Q

What is the colour change when an excess of AQUEOUS AMMONIA is added to a solution containing [Cr(H2O)6]3+ ?

A

VIOLET -> PURPLE

45
Q

What is the equation for the reaction when an excess of aqueous ammonia is added to [Cr(H2OO)6]3+?

A

[Cr(H2O)6]3 (aq) + 6NH3 (aq) -> [Cr(NH3)6]3+ (aq) + 6H2O (l)

46
Q

What are the two distinct steps of the reaction between [Cr(H2O)6]3+ and an excess of aqueous ammonia?

A

1) Initially a grey-green precipitate of Cr(OH)3 is formed.

2) The Cr(OH)3 precipitate dissolves in excess ammonia to form the complex ion [Cr(NH3)6]3+ .

47
Q

What is the complex called when carbon monoxide binds to the Fe2+ ion in haemoglobin?

A

Carboxyhaemoglobin

48
Q

What happens when carbon monoxide is breathed in?

A
  • A ligand substitution reaction takes place where the oxygen in haemoglobin is replaced by carbon monoxide.
  • Carbon monoxide binds to haemoglobin more strongly than oxygen, so a small concentration of carbon monoxide in lungs can prevent a large proportion of haemoglobin molecules from carrying oxygen.
  • The bond is so strong that the process is irreversible.
49
Q

What is a precipitation reaction?

A

The formation of a solid from a solution during a chemical reaction.

50
Q

When does a precipitation reaction occur?

A

It occurs when two aqueous solutions containing ions react together to form an insoluble ionic solid calling a precipitate.

51
Q

What is the observation when Cu2+ ions react with aqueous sodium hydroxide? (NaOH)

A
  • Blue solution reacts to form a blue precipitate of copper (II) hydroxide.
  • The precipitate is insoluble in excess NaOH.
    Cu2+ (aq) + 2OH- (aq) -> Cu(OH)2 (s)
52
Q

What is the observation when Fe2+ ions react with aqueous sodium hydroxide? (NaOH)

A
  • Pale green solution reacts to form a green precipitate of iron (II) hydroxide.
  • The precipitate is insoluble in excess NaOH but turns brown at its surface due to iron (II) being oxidised to iron (III).
    Fe2+ (aq) + 2OH- (aq) -> Fe(OH)2 (s)
    In air: Fe(OH2) (s) -> Fe(OH)3 (s)
53
Q

What is the observation when Fe3+ ions react with aqueous sodium hydroxide? (NaOH)

A
  • Pale yellow solution reacts to form an orange brown precipitate of iron (III) hydroxide.
  • The precipitate is insoluble in excess sodium hydroxide.
    Fe3+ (aq) + 3OH (aq) -> Fe(OH)3 (s)
54
Q

What is the observation when Mn2+ ions react with aqueous sodium hydroxide? (NaOH)

A
  • Pale pink solution reacts to form a light brown precipitate of manganese (II) hydroxide which darkens on standing air.
  • The precipitate is insoluble in excess sodium hydroxide.
    Mn2+ (aq) + 2OH- (aq) -> Mn(OH)2 (s)
55
Q

What is the observation when Cr3+ ions react with aqueous sodium hydroxide? (NaOH)

A
  • Violet solution reacts to form a grey-green precipitate of chromium (III) hydroxide.
    Cr3+ (aq) + 3OH- (aq) -> Cr(OH)3 (s)
  • The precipitate is soluble in excess sodium hydroxide forming a dark green solution.
    Cr(OH)3 (s) + 3OH- (aq) -> [Cr(OH)6]3- (aq)
56
Q

What is the observation when Cu2+ ions react with an excess of aqueous ammonia? (NH3)

A
  • 1st stage: precipitation reaction: Cu2+ (aq) + 2OH- (aq) -> Cu(OH)2 (s)
  • Cu(OH)2 is a blue precipitate which dissolves in excess ammonia to form a deep blue solution- [Cu(NH3)4(H2O)2]2+ .
57
Q

What is the observation when Cr3+ ions react with an excess of aqueous ammonia? (NH3)

A
  • 1st stage: precipitation reaction: Cr3+(aq)+ 3OH- (aq) -> Cr(OH)3 (s)
  • Cr(OH)3 is a green precipitate which dissolves in excess ammonia to form [Cr(NH3)6]3+ which is a purple solution.
58
Q

What is the reaction between Fe3+, Fe2+ and Mn2+ with an excess of aqueous ammonia?

A
  • They react in the same way as they react with aqueous sodium hydroxide, forming precipitates of Fe(OH)2 , Fe(OH)3 and Mn(OH)2.
  • There is no further reaction and so precipitates don’t dissolve.

A-Level Chemistry (27 decks)

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