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A-Level OCR Chemistry > Module 5: Chapter 24 (Transition Elements) > Flashcards

Module 5: Chapter 24 (Transition Elements) Flashcards

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1
Q

Where are d-block elements found on the periodic table?

A

between Group 2 and Group 13

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2
Q

What is the highest energy level for period 4?

A

from Sc to Zn 3d sub-shell has the highest energy level

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3
Q

What are d-block elements?

A
  • all metals, form metallic bonds
  • good conductors of heat and electricity
  • high melting and boiling points
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4
Q

What are some uses of d-block elements?

A

Cu, Ni, Zn and Ag are used in coins
Fe is used to make steel used in construction and tool making
Cu is used in water pipes and electrical wiring

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5
Q

What is the electron configuration of chromium?

A

[Ar]3d5 4s1

- half filled d-subshell

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6
Q

What is the electron configuration of copper?

A

[Ar] 3d10 4s1

- fully filled d sub-shell

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7
Q

Why do chromium and copper have half and fully filled sub-shells?

A

It is believed that the half-filled or fully filled d sub-shell gives additional stability to atoms of chromium and copper

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8
Q

When elements between Sc and Zn form ions, are electrons lost from 3d sub-shell first?

A

4s empties before 3d orbitals when forming an ion (4s fills before 3d when forming an atom, first in first out)

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9
Q

What are transition elements?

A

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

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10
Q

Why are Zn and Sc not transition elements?

A

both only form one ion without a partially filled d-orbital

Sc3+ = 1s2 2s2 2p6 3s2 3p6 (empty d-orbitals)
Zn2+ = 1s2 2s2 2p6 3s2 3p6 3d10 (full d-orbitals)
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11
Q

What are the properties of transition elements and their compounds?

A
  1. they can form compounds in which the transition element has different oxidation states
  2. they form coloured compounds
  3. many transition elements and their compounds can act as catalysts
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12
Q

Transition element property: variable oxidation states

A
  • each oxidation state has a characteristic colour
  • the number of oxidation states increases across the series to manganese and then decreases
  • a species containing a transition element in its highest oxidation state is often a strong oxidising agent (e.g. manganate (VII) ion MnO4^-)
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13
Q

Transition element property: formation of coloured compounds

A
  • compounds and ions of transition metals are frequently coloured
  • e.g. potassium dichromate (VI) is orange and hydrated copper (II) sulfate is blue
  • solid compounds can be dissolved in water to produce coloured solutions
  • colour of a solution is linked to the partially filled d-orbitals of the transition metal ion
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14
Q

Define what a catalyst does?

A

A catalyst is a substance that increases the rate of a chemical reaction without itself changing. It works by providing an alternative reaction pathway of lower activation energy.

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15
Q

Give an example of where a heterogeneous catalyst is used in industry?

A
  • an iron catalyst used in the Haber Process to make ammonia
  • Vanadium (V) Oxide (V2O5) is used in the Contact Process (manufacture of sulfuric acid), catalyses the reaction of 2SO2 + O2 <=> 2SO3
  • Nickel used in the hydrogenation of vegetable oils to make margarine
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16
Q

What is meant by a heterogeneous catalyst?

A

The catalyst is in a different state to the reactants

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17
Q

Transition elements property: catalysts

A

HOMOGENEOUS catalysts…
- Reaction between iodide ions and peroxodisulfate ions is catalysed by Fe2+(aq) ions
S2O8^2-(aq) + 2I-(aq) -> 2SO4^2-(aq) + I2(aq)
- How Fe2+ catalyses reaction…
Fe2+ reacts: S2O8^2- + Fe2+ -> 2SO4^2- + Fe3+
Fe2+ regenerated: Fe3+ + 2I- -> I2 + Fe2+

  • Reaction of zinc metal with acids is catalysed by the presence of Cu2+(aq) ions
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18
Q

What is an orbital?

A

A region around a nucleus where there is a high probability of finding an electron
- an orbital can hold up to 2 electrons with opposite spin

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19
Q

Describe an s-orbital?

A
  • sphere shape

- one occurs in every principal energy level

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20
Q

Describe a p-orbital?

A
  • dumb-bell shaped
  • 3 orbitals in the z, y and x axis
  • 3 orbitals occur in energy levels except the first
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21
Q

What is a complex ion

A

A complex ion is formed when one or more molecules or negatively charged ions (ligands) bond to a central metal ion

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22
Q

What is a ligand?

A

A ligand is 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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23
Q

What is a coordinate/dative covalent bond?

A

A shared pair of electrons in which the bonded pair has been provided by one of the bonding atoms only

24
Q

What is the coordination number?

A

The coordination number indicates the number of coordinate bonds attached to the central metal ion

25
Q

What is a monodentate ligand?

A

Able to donate one pair of electrons to a central metal ion

26
Q

What are the 5 common monodentate ligands?

A 
Water (H2O:) neutral charge
ammonia (:NH3) neutral charge
chloride (:Cl-) 1- charge
cyanide (:CH-) 1- charge
hydroxide (:OH-) 1- charge

: = which atom the lone pair is found on

27
Q

What is a bidentate ligand?

A

able to donate 2 pairs of electrons to a central metal ion

28
Q

What are the 2 common bidentate ligands?

A
  1. Ethanedioate (oxalate), (C2O4)2-
    - usually forms coordination number of 6
    - the negatively charged oxygens donate lone pairs to metal ion (other two oxygens have a double bond each with a carbon)
  2. 1,2-diaminoethane (shortened to en), H2NCH2CH2NH2
    - lone pairs found on both nitrogen atoms
    - coordination number is normally 6
29
Q

What to remember when drawing complex ions?

A
  • central metal ion (no charge)
  • ligans (bonded to correct atom)
  • 3D shape always
  • lone pairs and dative bonds
  • brackets with an overall charge of ion
30
Q

Shape of complex ions: six coordinate complexes

A
  • Octahedral shape
  • bond angle of 90º around the central metal ion
  • 6 coordinate bonds
31
Q

Shape of complex ion: four coordinate complexes (tetrahedral)

A
  • coordination number of 4
  • tetrahedral shape
  • bond angle of 109.5º around central metal ion
  • e.g [CuCl4]2-
32
Q

Shape of complex ion: four coordinate complexes (square planar complexes)

A
  • coordination number of 4
  • square planar shape
  • square planar occurs in complexes involving a transition metal with 8 d-electrons in the highest energy level (e.g. platinum (II), palladium (II) and gold (III))
33
Q

What is an example of a multidentate ligand?

A
  • EDTA^4- is a hexadentate ligand, bonds to the central metal ion 6 times
  • e.g. [Cu(EDTA]2-
  • forms 6 coordinate bonds
34
Q

What is stereoisomerism?

A

The same structural formula but a different arrangement of the atoms in space

35
Q

What are the 2 types of isomerism complex ions can display?

A
  • cis-trans isomerism

- optical isomerism

36
Q

Describe cis-trans isomerism in square planar?

A
  • no more than 2 identical ligands attached to the central metal ion
  • cis-isomer = 2 idental groups are adjacent to each other and the coordinate bonds between the identical ligands are 90º
  • trans-isomer = 2 identical groups are opposite each other and the coordinate bonds between the identical ligands are 180º
37
Q

Draw cis-platin and trans-platin

A

[Pt(NH3)2Cl2]
cis = Cl is 90º apart
trans = Cl is 180º apart
No overall charge on ion

38
Q

What is the role of cis-platin in the treatment of cancer?

A
  • cis-platin works by forming a platinum complex inside a cell which binds to DNA and prevents the DNA of the cell from replacing
  • activation of the cell’s own repair mechanism lead to apoptosis, or systematic cell death
39
Q

Describe cis-trans isomerism is octahedral complexes with monodentate and bidentate ligands?

A

MONO…

  • there must be 4 of one ligand and 2 of another
  • the 2 identical ligands are in cis-form when they are at 90º and trans-form when they are 180º apart (opposite)

BI…

  • 2 bidentate ligands and 2 identical ligands
  • 90º apart = cis-isomer
  • 180º apart = trans-isomer
40
Q

What are optical isomers?

A
  • optical isomers are stereoisomers that are non-superimposable mirror images of each other
  • e.g. [Co(NH2CH2CH2NH2)2Cl2]+ only the cis-form shows optical isomerism as the mirror image forms are non-superimposable (when the images are overlaid it does not overlap)
  • this can occur with 2 bidentate ligands with 2 mondentate ligands or with 3 identical bidentate ligands around central ions in octahedral complexes
41
Q

Cu2+

  • aqueous formula?
  • solution colour?
  • precipitate colour with NH3?
  • precipitate colour with NaOH?
A

[Cu(H2O)6]2+ forms pale blue solution

Adding NH3 = pale blue precipitate of Cu(OH)2
In excess ppt dissolves forming [Cu(NH3)4(H2O)2]2+ dark blue solution

Adding NaOH = pale blue precipitate of Cu(OH)2

42
Q

Fe2+

  • aqueous formula?
  • solution colour?
  • precipitate colour with NH3?
  • precipitate colour with NaOH?
A

[Fe(H2O)6]2+ forms a pale green solution

Adding NH3 = green ppt of Fe(OH)2
Iron (II) hydroxide will slowly oxidise into iron (III) hydroxide in air (an orange-brown ppt)

Adding NaOH = green ppt of Fe(OH)2
Iron (II) hydroxide will slowly oxidise into iron (III) hydroxide in air (an orange-brown ppt)

43
Q

Fe3+

  • aqueous formula?
  • solution colour?
  • precipitate colour with NH3?
  • precipitate colour with NaOH?
A

[Fe(H2O)6]3+ forms a yellow solution

Adding NH3 = orange-brown ppt of Fe(OH)3

Adding NaOH = orange-brown ppt of Fe(OH)3

44
Q

Mn2+

  • aqueous formula?
  • solution colour?
  • precipitate colour with NH3?
  • precipitate colour with NaOH?
A

[Mn(H2O)6]2+ forms a pale pink solution

Adding NH3 = light-brown ppt Mn(OH)2

Adding NaOH = light-brown ppt Mn(OH)2

45
Q

Cr3+

  • aqueous formula?
  • solution colour?
  • precipitate colour with NH3?
  • precipitate colour with NaOH?
A

[Cr(H2O)6]3+ forms a violet solution

Adding NH3 = green precipitate of Cr(OH)3
In excess ppt dissolves forming a purple solution of [Cr(NH3)6]3+

Adding NaOH = green precipitate of Cr(OH)3
In excess ppt dissolves into a dark green solution of [Cr(OH)6]3-

46
Q

What is the reaction of ammonia with water?

A

NH3(aq) + H2O(l) <=> NH4+(aq) + OH-(aq)

47
Q

The hydrated copper(II) ion is classed as a complex but he hydrates sodium ion is not. Explain why the hydrated sodium ion is not considered to be a complex ion

A
  • Oxygen atoms in water molecules have a partial negative charge
  • These form electrostatic attractions with sodium ion (ion-dipole bond) not a dative covalent bond
48
Q

Describe the structure of RBC

A
  • RBCs contain haemoglobin which are made up of 4 protein chains each of which has a haem group within the structure
  • Haem group is a complex ion with an Fe2+ central metal ion
  • This can bind to O2 gas in the lungs becoming oxyhaemoglobin
49
Q

Describe the haem group acting as a complex ion

A
  • Lone pair on 4 nitrogen form a coordinate bond with Fe2+
  • Iron can accept 2 more lone pairs, one above and below the plane
  • one of these comes from a nitrogen of an amino acid
  • the other is from an oxygen molecule (O2)
  • the O2 can be replaced by a water molecule (each easily replace each other)
  • Complex has a coordination number of 6
50
Q

What is the effect of CO?

A
  • Carbon Monoxide bonds irreversibly to haemoglobin (carboxyhaemoglobin) making it incapable of binding with any more oxygen
  • If the carboxyhaemoglobin concentration becomes high enough the result is death
51
Q

What is ligand substitution?

A

A ligand substitution reaction is one in which one ligand in a complex ion is replaced by another ligand.

52
Q

Describe the ligand substitution of [Cu(H2O)6]2+ and NH3

A

[Cu(H2O)6]2+ + 4NH3 -> [Cu(H2O)2(NH3)4]2+ + 4H2O
pale blue solution -> dark blue solution (caused by complex ions)
Ammonia is in excess
Both ions are in complex shape and second ion is in trans form (H2O 180º)
- forms a blue precipitate first which then dissolves in excess to the dark blue solution

53
Q

Describe the ligand substitution of [Cu(H2O)6]2+ and Cl-

A

[Cu(H2O)6]2+ + 4Cl- <=> [CuCl4]2- + 6H2O
pale blue solution <=> yellow solution (caused by complex ions)
equilibrium reaction
octahedral shape <=> tetrahedral shape
Cl- comes from concentrated hydrochloric acid

54
Q

Describe the ligand substitution of [Cr(H2O)6]3+ and NH3

A

[Cr(H2O)6]3+ + 6NH3 -> [Cr(NH3)6]3+ + 6H2O
violet solution -> purple solution
ammonia is in excess
both ions are in octahedral shape

55
Q

Describe the ligand substitution of [Cr(H2O)6]3+ and SO4^2-

A

[Cr(H2O)6]3+ + SO4^2- -> [Cr(H2O)5 SO4]+ + H2O

pale purple solution -> green solution

A-Level OCR Chemistry (21 decks)

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