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AQA A-Level Chemistry > Transition Metals > Flashcards

Transition Metals Flashcards

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1
Q

Define transition metal

A

A transition metal is one that forms at least one stable ion with a partially filled d subshell.

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2
Q

Which two elements are part of the d block but not considered transition metals?

A

Zinc and Scandium

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3
Q

Give the charge, electron configuration and reason as to why Scandium is not a transition metal.

A

Sc3+
[Ar] 4s0 3d0
Sc3+ is the only ion. The d subshell is empty.

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4
Q

Give the charge, electron configuration and reason as to why Zinc is not a transition metal.

A

Zn2+
[Ar] 4s0 3d10
Zn2+ is the only ion. The d subshell is full.

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5
Q

What are the two exceptions when writing electron configuration of transition metals?

A

Chromium (4s1 3d10)
Copper (4s1 3d10)

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6
Q

How are electrons lost from a transition metal?

A

First in, first out. So 4s are lost before 3d

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7
Q

4 features of transition metals

A
  1. Form complex ions
  2. Coloured ions
  3. Catalytic properties
  4. Variable oxidation states
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8
Q

Define coordinate bond.

A

A covalent bond is formed when both electrons are donated from the same atom.

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9
Q

Define ligand

A

A molecule/ion with a lone pair can form a coordinate bond with a metal ion.

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10
Q

Define coordination number

A

Number of coordinate bonds with the central metal ion

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11
Q

Define complex ion

A

Central metal ion surrounded by ligands

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12
Q

Monodentate ligand

A

Each ligand forms one coordinate bond

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13
Q

Bidentate ligand

A

Each ligand forms 2 coordinate bonds

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14
Q

Examples of monodentate ligands

A

H2O-:
Cl-:
:-NH3
:-CN

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15
Q

Examples of bidentate ligands

A

Ethane-1,2-diamine, or 1,2-diaminoethane (NH2CH2CH2NH2)
Ethanedioate ion (C2O4 2-)

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16
Q

Common shapes which transition metal complexes form

A

Octahedral
Square planar
Tetrahedral
Linear

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17
Q

What shape do complexes forming 6 coordinate bonds occupy? Give an example

A

Octahedral
Copper (II) Hexa Aqua Ion ([Cu(H2O)6]2+)

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18
Q

What shapes do complexes forming 4 coordinate bonds occupy? Give examples

A
  1. Tetrahedral
    Cobalt (II) Chloride Ion ([CoCl4]2-)
  2. Square Planar
    Nickel (II) Tetra Cyano Ion ([Ni(CN)4]2-)
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19
Q

What shape do complexes forming 2 coordinate bonds occupy? Give an example and its use.

A

Linear
Silver (I) Ammonia Ion ([Ag(NH3)2]+)
The active part of Tollens’ reagent used to distinguish between aldehydes and ketones

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20
Q

Example of a hexadentate ligand

A

EDTA 4-
Occupies octahedral shape
Two coordinate bonds from N atoms and four coordinate bonds from the O- ions

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21
Q

Why do chloro complexes tend to be tetrahedral?

A

The chloride ligand is too big to fit any more than 4 Cl- ligands around the metal ion

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22
Q

Show how the complex [Cu(H2O)6]2+ can be converted into [Cu(H2O)2(NH3)4]2+ and state the colour of the new complex

A

[Cu(H2O)6]2+ + 4NH3 <—-> [Cu(H2O)2(NH3)4]2+ + 4H2O
DEEP BLUE

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23
Q

When does the chelate effect occur?

A

When a monodentate ligand is substituted by a bidentate or multidentate ligand

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24
Q

An example of the chelate effect
[Cu(H2O)6]2+ + 3H2NCH2CH2NH2 <–> [Cu(H2NCH2CH2NH2)3]2+ + 6H2O

A

6 monodentate H2O ligands are replaced by 3 bidentate ethane-1,2-diamine ligands.
4 molecules on left turn into 7 molecules on right
Large increase in entropy
Thermodynamically very favourab;e
Entropy (ΔS) is positive.

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25
Q

EXAM STYLE QUESTION:
Explain why this reaction is feasible:
[Cu(NH3)6]2+ + 3H2NCH2CH2NH2 <–> [Cu(H2NCH2CH2NH2)3]2+ + 6NH3

A
  • Enthalpy change approximately zero
    = same number of Cu-N bonds broken and formed
  • Large increase in entropy, positive entropy
    = 7 molecules produced from 4 molecules
  • Therefore, ΔG= negative
26
Q

Bonding in haemoglobin

A

Made of central Fe2+ ion, forms 4 bonds to ring system called porphyrin.
- Bond in square planar arrangement- 4 coordinate bonds between Fe2+ and N atoms in haem structure.
- 1 coordinate bond between Fe2+ and globin protein.
- 1 coordinate bond between Fe2+ and O2 molecules.

27
Q

What happens when O2 molecule has been transported around the body to where it is needed?

A

Coordinate bond breaks releasing O2
CO2 can bond in its place to be transported to lungs

28
Q

Why is CO toxic?

A

CO is toxic because CO bonds more strongly to the Fe2+ in haemoglobin.
This prevents O2 from bonding to the Fe2+, causing suffocation.

29
Q

Steroisomer definition

A

Have same structural formula but different arrangement of atoms in space.

30
Q

Two types of stereoisomerism

A

Geometrical isomerism- Cis-trans isomerism
Optical isomerism- non-superimposable mirror images

31
Q

Example of octahedral complex with cis-trans isomerism

A

[CoCl2(NH3)4]+

32
Q

Example of square planar complex with cis-trans isomerism

A

[PtCl2(NH3)2]

33
Q

What is the cis isomer of [PtCl2(NH3)2] known as and what is it effective for?

A

Known as cisplatin
Effective anti-cancer drug

34
Q

How does cisplatin work to prevent DNA replication?

A

Cisplatin binds to DNA in cancer cells and stops cell replication. The 2 Cl- ions on Cisplatin are substituted for 2 N atoms on adjacent guanine bases.

35
Q

Example of cis-trans isomerism with bidentate ligand

A

[Cr(H2O)2(C2O4)2]-

36
Q

When does optical isomerism occur in complexes?

A

Complexes form with at least 2 bidentate ligands and 2 monodentate ligands
Structure has to be cis.

37
Q

What is optical isomerism

A

A form of stereoisomerism where the complex forms non-superimposable mirror images of itself.

38
Q

What is the only method of finding which isomer is present?

A

Using the fact that optical isomers rotate a plane of polarised light in opposite directions.

39
Q

Examples of optical isomer complexes

A

[Ni(H2NCH2CH2NH2)3]2+
[Co(H2O)2(C2O4)2)

40
Q

Why are transition metals coloured?

A

All have partially filled d subshells
All d orbitals are of equal energy= ground state
Presence of other atoms causes d orbitals to have change in energy
Enables e- to be excited from one d orbital to another.
Energy needed for transition taken from visible light
Colour of light absorbed missing from the light that reflects from substance.
Colour seen is reflected/transmitted.
Diff in energy between d subshells= ΔE

41
Q

ROY

A

Low energy

42
Q

BIV

A

High energy

43
Q

If a transition metal has small ΔE…

A
  • Low energy light (ROY) absorbed to excite e-
  • BIV reflected
  • Compound looks blue/purple
44
Q

If a transition metal has a big ΔE…

A
  • High energy light (BIV) absorbed to excite e-
  • ROY reflected
  • Compound looks red/orange
45
Q

What changes alter the colour of a compound

A

Change in LIGANDS
Change in OXIDATION STATE of metal
Change in COORDINATION NUMBER of complex
Change in SHAPE of complex

46
Q

Method to find concentration of unknown sample from callibration curve

A
  1. Measure the absorbance of known concentrations
  2. Plot graph of absorbance v. concentration
  3. Read value of concentration from measured absorbance of unknown from graph.
47
Q

Catalyst definition

A

Substance that increases ROR without being used up itself

48
Q

How do catalysts work

A

Decrease activation energy by providing alternative pathway

49
Q

Heterogenous catalyst definition

A

Catalyst is in different phase to reactants

50
Q

Homogeneous catalyst definition

A

Catalyst is in same phase as reactants

51
Q

Heterogeneous catalyst process

A
  1. Reactants ADSORB onto surface of catalyst on an active site.
  2. Reaction occurs on surface of catalyst.
  3. Products desorb from surface of catalyst.
52
Q

How to make catalyst efficient

A

Increase SA
Spread catalyst over inert support medium

53
Q

What happens when catalyst poisoning occurs?

A

Impurities can block active sites
Prevents reactants from adsorbing
Purifying reactants is the best way to prevent poisoning.

54
Q

Examples of heterogeneous catalysts

A
  1. Making ammonia in Haber process CATALYSED BY IRON
    N2 + 3H2 <–> 2NH3
  2. Making sulfuric acid in Contact process CATALYSED BY SOLID VANADIUM OXIDE (V2O5)
    SO2+ V2O5 <–> SO3 + V2O4
    2V2O4 + O2 <–> 2V2O5
    overall: 2SO2 + O2 <–> 2SO3
  3. Manufacture of methanol
    first forms synthesis gas: CH4 + H2O –> CO + 3H2
    then reaction catalysed by solid chromium oxide Cr2O3: CO + 2H2 –> CH3OH
55
Q

Example of homogeneous catalyst

A

Peroxodisulfate ions oxidise iodide ions to iodine.

56
Q

Why does uncatalysed reaction of peroxodisulfate ions// ethanedioic acid have high activation energy?

A

Uncatalyzed has high activation energy because 2 negative ions repel.

57
Q

Equations for example of homogeneous catalyst

A

Uncatalysed:
S2O8 2- + 2I- –> 2SO4 2- + I2
Catalysed by Fe2+:
1. S2O8 2- + 2Fe 2+ –> 2SO4 2- + 2Fe 3+
2. 2I- + 2Fe 3+ –> I2 + 2Fe 2+

58
Q

Autocatalyst definition

A

One product of reaction catalysed reaction as it proceeds further.

59
Q

Example of autocatalyst

A

Oxidation of ethanedioic acid by manganate ions

60
Q

Equations for example of autocatalyst

A

Uncatalysed:
2MnO4 - + 16H+ + 5C2O4 2- –> 2Mn2+ + 8H2O + 10CO2
Catalysed:
1. 4Mn2+ + MnO4- + 8H+ –> 5Mn3+ + 4H2O
2. 2Mn3+ + C2O42- –> 2CO2 + 2Mn2+
Purple to clearer

61
Q

Conc v time graph for this reaction

A
  1. Rate starts slow- no catalyst initially
  2. Two negatively charged reactants collide with a very high Ea
  3. Then some Mn2+ is formed, rate increases and reaction is being increasingly catalysed.
  4. Rate decreased and levels off at reactants used up.

AQA A-Level Chemistry (19 decks)

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