5I- Transition Metals Flashcards by Jena p

How are electrons arranged in transition metals

4s sub shell empties and fills before 3d subshell
This is also true for ions ie Fe 3+

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Definition of a transition metal and which ones are they

Form at least 1 stable ion with a partly filled d subshell

Ti, V, Cr, Mn, Fe, Co, Ni, Cu

Not transition metals are below
Sc forms a 3+ ion, no electrons in d subshell
Zn forms a 2+ ion, d subshell is filled with 10 electrons

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What properties do transition metals have

Complex formation, transition metal surrounded by other ions/molecules by coordinate bonds (ligands)
Formation of coloured ions, transition metals are coloured
Variable oxidation states, transition metals in compounds have multiple oxidation states, Cu+ and Cu2+
Catalytic activity, transition metals increase the rate of reaction without being used up

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What’s a ligand

Molecule or ion forming a coordinate bond with a transition metal by donating a pair of electrons

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What’s a complex

A central metal atom/ion surrounded by ligands

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Coordination number

The number of coordinate bonds to the central metal atom/ion surrounded

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What are monodentate ligands and give examples

Form one coordinate bond per ligand
H2O
NH3
Cl-

H2O and NH3 are a similar size and are uncharged

Cl- is a larger ligand than the other two

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What happens to coordination number when NH3 and H2O are exchanged as ligands

NH3 and H2O can be exchanged without changing the coordination number however the substitution may be incomplete
Affects Cu2+ Co2+

[Co(H2O)6]2+ + 6NH3 —> [Co(NH3)6]2+ + 6H2O

And

[Cu(H2O)6]2+ + 4NH3 —> [Cu(NH3)4(H2O)2]2+ + 4H2O

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What happens to coordination number if H2O and Cl- are exchanged

Adding conc HCL or saturated NaCl to an aq ion leads to ligand substitution

Coordination number changes
Affects Co2+ Cu2+ Fe3+

[Cu(H2O)6]2+ + 4Cl- —> [CuCl4]2- + 6H2O

[Co(H2O)6]2+ + 4Cl- —> [CoCl4]2- + 6H2O

[Fe(H2O)6]2+ + 4Cl- —> [FeCl4]2- + 6H2O

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What’s a bidentate ligand and examples

Contain two atoms with lone pairs (one lone pair on each atom) which can form two coordinate bonds per ligand

NH2CH2CH2NH2
C2O4-

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Lone pairs and structure of bidentate ligands

Mind map

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Equations to show formation of bidentate complexes with NH2CH2CH2NH2 and C2O4 2-

[Cu(H2O)6]2+ + 3NH2CH2CH2NH2 —> [Cu(NH2CH2CH2NH2)3]2+ + 6H2O

[Cu(H2O)6]2+ + 3C2O4 2- —> [Cu(C2O4)3]4- + 6H2O

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Equation and conditions for partial substitution of C2O4 2- ions

Dilute aq C2O4 2- added to aq Cu 2+

Water molecules are replaced

[Cu(H2O)6]2+ + 2C2O4 2- —> [Cu(C2O4)2(H2O)2]2- + 4H2O

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What are multidentate ligands and give example

Give an equation to show formation of this ligand

More than two atoms with a lone pair of electrons which bond to a transition metal ion

EDTA 4-

[Cu(H2O)6]2+ + EDTA4- —> [Cu(EDTA)]2- + 6H2O

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What’s haem

Fe2+ complex with a multidentate ligand

Oxygen forms a coordinate bond to Fe2+ in haemoglobin, oxygen can be transported in the blood

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Why is carbon monoxide toxic

CO replaces the O2 which is coordinate bonded to the Fe2+ in haemoglobin

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What’s the chelate effect and explain it

Bidentate and multidentate ligands replace monodentate ligands forming more stable complexes
Eg
[Cu(H2O)6]2+ + EDTA 4- —> [Cu(EDTA)]2- + 6H2O

Reactions have an increased entropy, more moles of product than reactant and therefore more disorder
Enthalpy change is small as there are a similar number of bonds in both complexes
Delta s (entropy) is positive, delta H (enthalpy) is 0, therefore delta G (gibs free energy) is negative

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Shapes of complex ions

Etc etc etc

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What complexes are formed by transition metal ions and small ligands
Name the ligands

Octahedral complexes
Forms 6 bonds, therefore a coordination number of 6
90° bond angle

NH3 and H2O
Bidentate ligands NH2CH2CH2NH2 and C2O4 2-

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What type of isomerism do octahedral complexes display

Monodentate ligands display [E] [Z] isomerism

Bidentate ligands display optical isomerism

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Why type of complex do larger ligands form with transition metal ions
Name the ligand

Tetrahedral complexes
4 bonding pairs, therefore coordination number of 4
Cl-
109.5° bond angle

What type of complexes are formed by Pt2+ and Ni2+ metal ions

Square planar
4 bonding pairs, therefore a coordination number of 4
90° bond angle

What type of isomerism do square planar complexes have
And what type of isomer is cis platin

[E] [Z]

Cisplatin is the cis isomer which is the [Z] isomer

What type of complexes do Ag+ metal ions form
Give an example of an Ag+ complex

Linear
2 bonding pairs, therefore a coordination number of 2
[Ag(NH3)2]+, used in tollens reagent

Why do transition metals have colours

Transition metals have part filled d orbitals In a compound, other atoms nearby make the d orbital split causing it to have different energies Some wavelengths of visible light is absorbed Electrons move from a lower energy level (ground state) to a higher energy level (excited state) The change between the split orbitals is the energy change (^E) Light energy transmitted or reflected gives the colour we see

Equation for energy change (^E)

^E = hv = hc/wavelength ^E energy change (J) h= planks constant v= frequency of light (Hz) c= speed of light (m/s) Wavelength= (m)

What does the colour of ions depend on

Oxidation state Coordination number Ligands These cause ^E to change causing colour to change

What’s the absorption of light used in

Spectroscopy

How to determine the conc of coloured ions in a solution

Colourimeter Light passes through a sample Compare the absorbance value of unknown sample with that against a graph of known concentrations

What are the two types of catalysts

Homogenous and heterogenous

What’s a homogenous catalyst

The catalyst is in the same phase as the reactants

What’s a heterogenous catalyst

A catalyst in a different phase to the reactants

How does a heterogenous catalyst work

Occurs at active sites at the surface of catalyst Reactants adsorb to the active site Bonds in the reactants weaken and break, molecules held in the correct orientation or higher conc of reactants at the surface increase collision frequency

How is surface area of a heterogenous catalyst maximised to minimise cost

Use of a support medium Rh is placed on a ceramic support in catalytic converters

What determines whether a metal has a string adsorbance or a low adsorbance

e- in the 3d and 4s sub shell If adsorption is too strong products won’t be released If adsorption is too weak reactants won’t be adsorbed Ni and Pt have the correct strength

What is the catalyst for the contact process give eq

V2O5, it is regenerated SO2 + V2O5 —> SO3 + V2O4 2V2O4 + O2 —> 2V2O5 Overall 2SO2 + O2 —> 2V2O5

What’s the catalyst for the haber process give eq

Fe N2 + 3H2 —> 2NH3

What is a problem with heterogenous catalysts

Poisoning Active sites blocked by impurities Reduces efficiency, expensive to replace Catalyst may also be lost from the support medium

How do homogenous catalysts work

Reaction proceeds through an intermediate species The intermediate will have a diffferent oxidation state to the OG transition metal but at the end it will return to its initial oxidation state

What’s the catalyst for a reaction between S2O8 2- and I - give eq

Fe 2+ S2O8 2- + 2Fe 2+ —> 2SO4 2- + 2Fe 3+ 2Fe 3+ + 2I - —> 2Fe 2+ + I2 Overall S2O8 2- + 2I - —> 2SO4 2- + I2 Fe 3+ (123, I (1-) —> I2 using Fe 3+) 2Fe 3+ + 2I - —> 2Fe 2+ + I2 S2O8 2- + 2Fe 2+ —> 2SO4 2- + 2Fe 3+ Overall S2O8 2- + 2I - —> 2SO4 2- + I2

Why is the reaction between I- and S2O8 2- ions slow

High activation energy is needed as there is repulsion between 2 -ve ions

How to workout out if a substance can be a homogenous catalyst

It’s electrode potential (E value) should lie in between the electrode potentials from the two reactants Reactant with a more +ve electrode potential will be reduced Reactant with a more -ve electrode potential will be oxidised after

What’s autocatalysis

One of the products from a reaction can catalyse the reaction

What’s the catalyst for C2O4 2- and MnO4 - give eq

Mn 2+ 4Mn 2+ + MnO4- + 8H+ —> 5Mn 3+ + 4H2O 2Mn 3+ + C2O4 2- —> 2Mn 2+ + 2CO2 Overall 2MnO4 - + 5C2O4 2- 16H+ —> 2Mn 2+ + 10CO2 + 8H2O

Describe the rate of reaction between MnO4- and C2O4 2-

Slow initially as it is uncatalysed, two -ve ions require a high activation energy Mn2+ ions produced act as an auto catalyst reaction begins to speed up As MnO4 - conc drops reaction slows

What oxidation states do transition metals have

Variable oxidation states

What are common oxidation states for vanadium, give formula for them

Vanadium(V) is reduced by zinc in an acidic solution to produce vanadium (IV) (III) and (II) V 2+ (oxidation state +2) V 3+ (oxidation state +3) VO 2+ (oxidation state +4)

What’s redox potential

The tendency of a species to be reduced by accepting e- or be oxidised by donating e-

What influences an transition metals ion changing from a higher oxidation state (+3) to a lower oxidation state (+2)

pH Ligand

What is tollens reagent used to distinguish

Difference between aldehydes and ketones

Equations for the reaction of [Ag(NH3)2]+ tollens reagent

Reduction eq [Ag(NH3)2]+ + e- —> Ag + 2NH3 Oxidation eq CH3CHO + H2O —> CH2CO2H + 2H+ + 2e-