Transition Metals Flashcards by Taia Sellars

Define a transition metal

d-block elements that form one or more stable ions with incompletely filled d-orbitals

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What does it mean to show variable oxidation numbers

transition metals forming multiple stable ions
each ion the transition metal has a different oxidation number (e.g. vanadium has four stable oxidation numbers)

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name 4 properties of transition metals

variable oxidation numbers
form complex ions
ions are often coloured in solution
act as good catalysts

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why do transition metals show variable oxidation numbers

transition metals form ions by removing electrons from both their 3d and 4s subshells
these subshells are of similar energy levels
so similar successive ionisation energies

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what is a complex ion

central metal ion surrounded by dative covalently bonded ligands

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what is a ligand

an atom, ion or molecule that donates a pair of electrons to a central metal atom or ion (forms a dative covalent bond)

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name and define the three types of ligands

monodentate –> ligands with one lone pair of e-
bidentate –> ligands with two lone pairs of e- and can form two dative covalent bonds with the metal ion
multidentate –> ligands with 2 or more lone pairs of e-

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given an example of a bidentate ligand

1,2-diaminoethane
NH2CH2CH2NH2

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Give an example of a multidentate ligand

EDTA4-
(hexadentate ligand)

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give an example of a multidentate ligand in the body

Haemoglobin an iron II complex containing multidentate ligand called a Haem group
Haem group made up of a ring containing 4 N atoms ( can form 4 dative covalent bonds with Iron II )

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define coordination number

number of dative covalent bonds formed with the central metal ion

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what shape do six-fold coordination complexes have

octahedral

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why do complexes with different coordination numbers have distinct shapes

bonding electrons of the dative covalent bonds repel each other
so ligands positioned as far away from each other as possible

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what shape do four-fold coordination complexes have

tetrahedral

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what ligand generally forms four-fold complexes

Cl- (large ligand)

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most common shapes of coordination complexes

octahedral
tetrahedral
square planar

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what type of complex ions display what type of isomerism

tetrahedral + square planar
Cis/trans

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what is used as a drug for cancer and what do you need to look out for with this drug

cis-platin (a complex of platinum II)
trans-platin is toxic, so must ensure only cis-platin is given to patients

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What happens when ligands bond to transition ions

3d orbitals are split Into 2 different energy levels

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What does the size of the energy gap between split 3d orbitals indicate

The frequency of light absorbed

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What factors influence the amount of energy needed to make electrons jump up to the higher 3d energy levels

Of the central metal ion:
- oxidation number
- ligands
- coordination number

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What causes complex ions/aqueous ions to display a specific colour

ligand binding results in 3d orbitals splitting to different energy levels
difference in energy level determines frequency of light absorbed
light frequency not absorbed is transmitted or reflected, and combine to make the colour that is displayed

What causes a compound to look white or colourless

no 3d electrons/ 3d sub hell is full
no electrons jump, no energy is absorbed, so no frequency of light absorbed

Vanadium +5 ion + colour

- VO2^+ - Yellow

Vanadium +4 ion + colour

- VO^2+ - Blue

Vanadium +3 ion + colour

- V3+ - green

Vanadium +2 ion + colour

- V2+ - violet

Chromium +6 ion + colour

- Cr2O7^2- - orange

Chromium +3 ion + colour

- Cr3+ - green

Iron +3 ion + colour

- Fe3+ - yellow

Iron +2 ion + colour

- Fe2+ - pale green

Cobalt +2 ion + colour

- Co2+ - pink

Copper +3 ion + colour

- Cu2+ - pale blue

What is ligand exchange

One ligand swapped for another ligand

What happens to the complex ion if ligand exchange occurs on ligands of similar size

- coordination number of complex ion is the same - shape is the same

What happens to the complex ion if ligand exchange reaction occurs with ligands different in size

- change in coordination number and change of shape

[Cr(H2O)6]3+ (aq) + 6NH3(aq) <=>

[Cr(NH3)6]3+ (aq) + 6H2O(l) - colour change green-purple - octahedral shape - octahedral shape

[Co(H2O)6]2+ (aq) + 4Cl- (aq) <=>

[CoCl4]2- (aq) + 6H2O(l) - colour change pale pink to blue - octahedral to tetrahedral shape

[Cu(H2O)6]2+ (aq) + 4NH3(aq) <=>

[Cu(NH3)4(H2O)2]2+ (aq) + 4H2O - colour change pale blue to deep blue - octahedral to octahedral shape (partial ligand substitution)

[Cu(H2O)6]2+ (aq) + 4Cl- <=>

[CuCl4]2- (aq) + 6H2O(l) - colour change pale blue to yellow - octahedral to tetrahedral shape

Precipitate reactions: [Cu(H2O)6]2+ (aq) —> + OH- —> + NH3 (not excess)

—> [Cu(H2O)6]2+ (aq) + 2OH- (aq) —> [Cu(OH)2(H2O)4](s) + 2H2O —> [Cu(H2O)6]2+ (aq) + 2NH3 (aq) —>[Cu(OH)2(H2O)4](s) + 2NH4+ (aq) Pale blue solution - blue precipitate

Precipitate reactions: [Fe(H2O)6]2+ (aq) —> + OH- —> + NH3

—> [Fe(H2O)6]2+ (aq) + 2OH- (aq) —> [Fe(OH)2(H2O)4](s) + 2H2O(l) —> [Fe(H2O)6]2+ (aq) + 2NH3 (aq) —>[Fe(OH)2(H2O)4](s) + 2NH4+ (aq) Pale green solution - green precipitate Green precipitate darkens on standing (is oxidised to Iron(III) hydroxide)

Precipitate reactions: [Fe(H2O)6]3+ (aq) —> + OH- —> + NH3

—> [Fe(H2O)6]3+ (aq) + 3OH- (aq) —> [Fe(OH)3(H2O)3](s) + 3H2O(l) —> [Fe(H2O)6]3+ (aq) + 3NH3 (aq) —> [Fe(OH)3(H2O)3](s) + 3NH4+ (aq) Yellow solution - orange precipitate Orange precipitate darkens on standing

Precipitate reactions: [Co(H2O)6]2+ (aq) —> + OH- —> + NH3 (not excess)

—> [Co(H2O)6]2+ (aq) + 2OH- (aq) —> [Co(OH)2(H2O)4](s) + 2H2O(l) —> [Co(H2O)6]2+ (aq) + 2NH3 (aq) —> [Co(OH)2(H2O)4](s) + 2NH4+ (aq) Pale pink solution - blue precipitate Blue precipitate turns brown on standing

Precipitate reactions: [Co(OH)2(H2O)4](s) —> + NH3 (excess)

—> [Co(OH)2(H2O)4](s) + 6NH3(aq) —> [Co(NH3)6]2+ (aq) + 2OH- (aq) + 4H2O(l) blue precipitate dissolves to form a yellow-brown solution

Why are transition metals good catalysts

- they change oxidation number by gaining or losing electrons within their d-orbitals - so can transfer electrons to speed up reactions

What is the contact process and what acts as a catalyst

- SO2 is oxidised to SO3 - V2O5 (Vanadium (V) oxide) acts as a catalyst

Reactions within contact process

—> Vanadium oxidises SO2 to SO3 V2O5 + SO2 —> SO3 + V2O4 (Vanadium (V) to Vanadium (IV)) —> Vanadium (IV) oxide then reduced back to original state V2O4 - 1/2O2 —> V2O5

Describe how a catalytic converter works (heterogeneous catalyst)

- adsorption of reactant molecules onto the surface of the catalyst - weakening of bonds between the reactants atoms + activation of the molecules so they react more easily - desorption of product molecules from the catalyst

What is a homogenous catalyst and how does it work

- a catalyst in the same phase as the reactants - combines the reactants to form an intermediate species, which will then react to form the products and reform the catalyst

What catalyst is used in peroxodisulfate ions oxidising iodide ions + why is the reaction without the catalyst slow

- Fe2+ - both ions negatively charged so they repel each other and are unlikely to collide and react

Peroxodisulfate ions oxidising iodide ions + Fe2+ catalyst reactions

S2O82- (aq) + 2Fe2+ (aq) —> 2Fe3+ (aq) + 2SO4-2 (aq) ((Fe2+ oxidised)) 2Fe3+ (aq) + 2I- (aq) —> I2 (aq) + 2Fe2+ (aq) ((Fe2+ is regenerated))

What is an autocatalyst

- catalyst is a product of the reaction and acts as a catalyst for the reaction - reaction progresses, amount of product increases, reaction rate increases

Give an example of an autocatalyst

Mn2+

All reactions with MnO4- + C2O42-

—> 2MnO4- (aq) + 16H+ (aq) + 5C2O4^2- (aq) —> 2Mn2+ (aq) + 8H2O(l) + 10CO2(g) - 4Mn2+ (aq) + MnO4- (aq) + 8H+ (aq) —> 5Mn3+ (aq) + 4H2O(l) - 2Mn3+ (aq) + C2O4^2- (aq) —> 2Mn2+ (aq) + 2CO2(g)