transition metals theory

formal definition of a transition element

an element that forms at least one stable ion with a part full d-shell of electrons.

why are scandium and zinc d-block elements, but not transition elements?

scandium only forms Sc^(3+)(3d0) in all its compounds, and zinc only forms Zn^(2+)(3d10) in all its compound.

4 bullet point features of transition metals

variable oxidation states, coloured ions, catalytic activity, complex formation

what is meant by the property ‘variable oxidation states’?

transition metals have more than one oxidation state in their compounds. they can thus take part in many redox reactions.

what is meant by the property ‘complex formation’?

transition metals form complex ions. a complex ion is formed when a transition metal ion is surrounded by ions or molecules, collectively called ligands, which are bonded to it by coordinate bonds.

what bonds are involved in the formation of complex ions?

coordinate bonds

what is a ligand

an ion or molecule with a lone pair of electrons that forms a coordinate bond with a transition metal.

what is coordination number

the number of coordinate bonds to lifands that surround the d-block metak ion

what is the normal shape of complexes with coordination number 6?

octahedral

what is the normal shape of complexes with coordination number 4?

square planar or tetrahedral

what are multidentate ligands?

ligands with more than one atom with a loe pair of electrons which can bond to a transition metal ion

name 3 bidentate ligands

ethane-1,2-diamine. ethanedioate. benzene-1,2,-diol

explain the ethane-1,2-diamine ligand (structuralformula, where bonds come from, other names, charge)

NH2CH2CH2NH2. lone pair on each nitrogen. often abbreviated to en. neutral.

name this molecule

ethane-1,2-diamine or en

explain the ethanedioate ligand (structural formula, where bonds come from, other names, charge)

C2O4^(2-). lone pair on each single bonded oxygen. oxalate. 2-.

name this molecule

ethanedioate or oxalate

explain the benzene-1,2-diol ligand (formula, where bonds come from, other names, charge)

C6H4(OH)2. lone pair on each oxygen of alcohol groups. 1,2-dihydroxybenzene. neutral.

name this molecule

benzene-1,2-diol

name an important multidentate ligand

EDTA^4-

what does EDTA^4- stand for and what is it?

ethylenediaminetetracetate, a hexadentate ligand

name this molecule

EDTA^4-, ethylenediamenetetracetate

where do the coordinate bonds for from with EDTA?

4 single bonded oxygens, 2 nitrogens

what are chelates?

complex ions with polydentate ligands

what can chelates be used for

effectively removing d-block metal ions from solution

what happens if you add a hexadentate ligand to a solution of a transition metal salt?

the EDTA will replace all 6 waterligands in the aqua ion

write the equation for adding EDTA to a solution of a copper salt

[Cu(H2O)6]^(2+)(aq) + EDTA^(4-)(aq) → [CuEDTA]^(2-)(aq) + 6H2O(l)

what is the chelate effect? (not explain)

chelate complexes with polydentate ligands are favoured over complexes with monodentate ligands in the removal of d-block metal ions from solution.

explain the chelate effect:

using a multidentate ligand (instead of a monodentate ligand) means there will be a greater number of product particles than reactant particles. this means there will be an increase in entropy which drives the reactant to the right.

what can bi/multidentate ligands do instead of bonding to the same metal to form a ring

the ligand sites can bond to two different metal ions and act as a bridge

why are most transition metal compounds coloured? (6 sentences)

transition metal compounds have part-filled d-orbitals. it is therefore possible for electrons to move from one d-orbital to another. in an isolated transition metal atom, all the d-orbitals are of exactly the same energy, but in a compound, the presence of other atoms means the d-orbitals have slightly different energies. when electrons move from one d-orbital to another of a higher energy they absorb energy in the visible region of the spectrum equal to the difference in energy between levels. this colour is therefore missing from the spectrum. observed is a combination of all the colours not absorbed.

what is the equation relating energy, frequency, and Planck’s constant?

delta E = hv = hc/lambda

violet light is of what kind of energy and frequency

high energy, high frequency

red light is what kind of energy and frequecny

low energy, low frequency

what does delta E depend on?

the oxidation state of the metal, the ligand, the complex shape

how can the frequencies a complex absorbs be measured

a UVvisible spectrometer

what is the relationship between uv/vis light and concentration

the more concentrated the solution, the more light absorbed

what can be added to intensify the colours of some ions

ligands, e.g. SCN^-

explain the variable oxidation states used in Tollen’s

as the aldehyde is oxidised to a carboxylic acid, the colourless Ag(+1) in [Ag(NH3)2]^+ is reduced to Ag(0) in silver mirror

explain the variable oxidation states used in Fehlings

as the aldehyde is oxidised to a carboxylic acid, the blue Cu^(+2) is reduced to brick red Cu(+1) in Cu2O

explain the variable oxidation states in K2Cr2O7

as alcohol/aldehyde is oxidised, the orange Cr(+6) in Cr2O7^(2-) is reduced to green Cr(3+)

what affects how easy it is to change the oxidation state of a transition metal?

the pH and the ligands present

in general, is it easier to oxidise or reduce a transition metal in alkaline conditions?

oxidise

in general, is it easier to oxidise or reduce a transition metal in acidic conditions?

reduce

how can you show that it is easier to reduce a transition metal in acidic conditions?

using electrode potentials

write the half equation for the reduction of Mn(VII) to Mn(II)

MnO4^-(aq) + 5e^- + 8H^+(aq) → Mn^(2+)(aq) + 4H2O(l)

write the half equation for Fe(II) to Fe(III)

Fe^(2+)(aq) → Fe^(3+)(aq) + e^-

write the full ionic equation for the oxidation of iron (II) to iron (III) using potassium manganate (VII)

5Fe^(2+)(aq) + MnO4^-(aq) + 8H^+(aq) →5Fe^(3+)(aq) + Mn^(2+)(aq)+ 4H2O(l)

what is the colour change for the oxidation of iron (II) to iron (III) using potassium manganate (VII)

deep purple to colourless

colour of Fe^(2+)

pale green

colour of MnO4^-

intense purple

colour of Fe^(3+)

pale violet

colour of Mn^(2+)

pale pink

what conditions should the oxidation of Iron (II) to Iron (III) using potassium mangate be done under

acidic

which acid should be used for the oxidation of Iron (II) to Iron (III) using potassium mangate

sulfuric acid

why should sulfuric acid be used in the oxidation of Iron (II) to Iron (III) using potassium mangate instead of hydrochloric?

E standard values show that manganate ions will oxidise chloride ions to chlorine (the emf value is positive). this would affect the titration because the manganate ions must be used only to oxidise Fe^(2+) ions. manganate ions do not oxidise sulfate ions.

what are heterogeneous catalysts

catalysts present in a reaction in a different phase than the reactants

what state are heterogeneous catalysts usually present as?

solids

give two ways to make heterogeneous

increase their surface area. spread the catalyst onto an inert support medium.

what is poisoning

the surface if the catalyst becoming covered with unwanted impurities.

why does spreading the catalyst onto an inert support medium make heterogeneous catalysts more efficient?

it increases the surface:mass ratio

what is the catalyst for the haber process?

iron in pea sized lumps

how long does the iron catalyst last for in the haber process? what happens to it?

around 5 years. it becomes poisoned by impurities in the gas stream like sulfur compounds

what is produced from the Contact Process

sulfuric acid

what is a homogeneous catalyst

when the catalyst is in the same phase as the reactant.

what happens when a homogeneous catalyst is used (and not a heterogeneous one)

an intemediate species is formed

write the overall ionic equation for peroxodisulfate ions oxidising iodide ions to iodine

S2O8^(2-)(aq) + 2I^-(aq) → 2SO4^(2-)(aq) + I2(aq)

what catalyses the reactopm betweem peroxodisulfate ions oxidising iodide ions to iodine?

Fe^(3+) ions

write both steps of the catalysed redox reaction between peroxodisulfate ions and iodide ions (catalysed by iron(II) ions

1) S2O8^(2-)(aq) + 2Fe^(2+)(aq) → 2SO4^(2-)(aq) + 2Fe^(3+)(aq). 2) 2Fe^(3+)(aq) + 2I^-(aq) → 2Fe^(2+)(aq) + I2(aq)

why does the uncatalysed reaction between peroxodisulfate ions and iodide ions have such high activation energy?

it takes place between two ions of the same negative charge, which repel, so it has a high activation energy.

give an example of an autocatalysed reaction. what is the catalyst?

ethanedioic acid + potassium manganate (VII). Mn^(2+)

which titration is used to find the concentration of potassium manganate (VII) in solution?

titration of ethanedioic acid and potassium manganate

write the ionic equation for potassium manganate + ethanedioic acid

2MnO4^-(aq) + 16H^+(aq) + 5C2O4^(2-)(aq) → 2Mn^(2+)(aq) + 8H2O(l) + 10CO2(g)