Chapter 24 - Transition Metals

d-block elements are all…

metallic → high melting and boiling points, shiny, conducting electricity + heat

chromium + copper both have atypical electron configurations, ending in

3d⁵ 4s¹ → a half-filled d subshell believed to give stability

in 4s subshells…

electrons are added to 4s subshells first, and removed from 4s subshells

transition element def.

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

Scandium only forms an ions with a charge of…

3+

Zinc only forms an ion with…

2+ charge

properties of transition metals:

1. form compounds in which the transition metal has different oxidation state

2. form coloured compound

3. the elements and their compound can act as a catalyst

Ti3+ colour:

light purple

V2+ colour:

light purple

V3+ colour:

green

V+4 colour:

blue

V+5 colour

yellow

Cr+2 colour

blue

Cr+3 colour

green

Cr+6 colour

orange

Mn2+ colour

pale pink

Mn2+ colour

dark pink

Mn+6 colour

green

Mn+7 colour

light purple

Fe2+ colour

pale green

Fe3+ colour

pale yellow

Co+2 colour

pink

Co+3 colour

green

Ni+2 colour

green

Copper +2 colour

blue

Cobalt Chloride is…

pink-purple

potassium dichromate (VI)

orange

nickel (II) sulphate colour

green

hydrated copper (II) sulphate colour:

blue

the colour of a solution can vary with…

different oxidation states

Haber Process

• the manufacture of ammonia

• uses finely divided iron as a catalyst

• N_2(g) + 3H_2(g) ⇌ 2NH_3(g)

Contact process:

• the production of a sulphur trioxide from the oxidation of sulphur dioxide.

• Catalysed by Vanadium Oxide V₂O₅:

• 2SO_2(g) + O_2(g) ⇌ 2SO_3(g)

Hydrogenation of vegetable fats:

Alkene + H₂ → (nickel catalyst) → alkane

Catalytic decomposition of hydrogen peroxide forming oxygen, with a transition metal catalyst:

2H₂O_2(aq) → 2H₂O(l) + O_2(g)

uses manganese (IV) oxide, MnO₂ as the catalyst

reaction between iodide ions and peroxodisulphate, S₂O₈^2- is catalysed by Fe²⁺ ions:

Fe²⁺(aq) reacts: S₂O₈^2-(aq) + Fe²⁺(aq) → 2SO₄^2-(aq) + Fe³⁺(aq)

Fe²⁺(aq) regenerated: Fe³⁺(aq) + 2I^-(aq) → I₂ + Fe²⁺_(aq)

Although Fe²⁺ is used up in the first step, it is regenerated in the second step → Overall, Fe²⁺ ions are not consumed.

A complex ion is formed…

when one (or more) molecules, or negatively charged ions, bond to a central metal ion.

These molecules are known as ligands.

Ligand definition:

A molecule or ion that donates a pair of electrons to a central metal ion to form a co-ordinate/dative covalent bond.

Dative covalent bond / co-ordinate bond def.

Covalent bond where one of the bonded atoms provides both the electrons in the shared pair

Co-ordination number of a complex ion:

the number of co-ordinate bonds attached to the central metal ion

overall charge on a complex ion =

the sum of the charges in the central metal ion and any ligands present

monodentate ligand definition:

a ligand that is able to donate one pair of electrons to a central metal ion

the water and ammonia ligands are both…

neutral

chloride, cyanide, hydroxide ligands are all…

negatively charged (-1 charge)

bidentate ligands:

a ligand that can donate two pairs of electrons to the central metal ion, forming 2 co-ordinate bonds

2 most common bidentate ligands:

1,2-diaminoethane (frequently shortened to ‘en’)

ethanedioate

what is the co-ordination number of this complex ion?

6 → there are 3 ligands, each forming 2 co-ordinate bonds

most common co-ordinate numbers of complex ions:

4 and 6

tetrahedral complexes:

1. the most common of the shapes with a co-ordinate number of 4

2. bond angles of 109.5 degrees around the central metal ion

square planar complexes:

occurs in complex ions of transition metals with 8 d-electrons in the highest energy d-subshell

Platinum (II), palladium (II), and gold (III)

Draw the square planar complex of [Pt(NH₃)₄]^2+:

draw the 3D tetrahedral complex of [CoCl₄]^2-

What 2 kinds of optical isomerism can complex ions display?

1. cis-trans isomerism

2. optical isomerism

Cis-trans isomerism in square planar complexes:

1. no C=C bond → different orientations about the central metal ion.

2. has no more than 2 identical ligands attached to the central metal ion .

Draw the cis-trans isomers of [Pd(NH₃)₂Cl₂] in 3D diagrams:

What kind of octahedral complex can form cis-trans isomers?

Containing four of 1 type of ligand + 2 of another type of ligand

draw the cis-trans isomers of [Co(NH₃)₄Cl₂]⁺

when drawing isomers, ensure that the bond to the metal ion comes from the atom in the ligand that…

has the lone pair

Octahedral complexes containing bidentate ligands can also show...

cis-trans isomerism → IF there are 2 or more!

Cis-trans isomerism of [Co(NH₂CH₂CH₂NH₂)₂Cl₂]⁺

what is the common ligand, 1,2-diaminoethane commonly abbreviated to?

‘en’

optical isomers def.

non-superimposable mirror images

ligand substitution def.

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

ligand substitution with chloride ions: Cu²⁺ with excess Cl^- ions:

[Cu(H₂O)₆]²⁺_(aq) + 4Cl^-_(aq) ⇌ [CuCl₄]^2-_(aq) + 6H₂O_(l)

_{pale blue solution (octahedral) yellow solution (tetrahedral)}

What happens in Chromium (III) sulphate is dissolved in water…

[Cr(H₂O]₅SO₄]⁺ is formed → one of the water ligands is replaced by a sulphate ion

When excess ammonia is added to Chromium (III)…

1. a grey-green precipitate of Cr(OH)₃ is formed

2. the Cr(OH)₃ precipitate dissolves in excess ammonia, forming the complex ion [Cr(NH₃)₆]³⁺

Ligand substitution in blood:

1. haemoglobin has 4 protein chains

2. each protein chain has a haem molecule

3. the central metal ion in a haem group is Fe²⁺ → can bind to O₂

4. as blood → lungs, haemoglobin bonds to oxygen

   1. oxyhaemoglobin forms

If CO is breathed in…

a ligand substitution takes place:

1. oxygen in haemoglobin is replaced by carbon monoxide

2. CO binds to haemoglobin more strongly than oxygen

3. small conc. of CO in the lungs prevents a large proportion of haemoglobin molecules from carrying oxygen

4. if the conc. of carboxyhaemoglobin becomes too high, you die

when does a precipitation reaction occur?

when two aqueous solutions containing ions react together to form an insoluble ionic solid, called a precipitate

Fe²⁺_(aq) + 2OH^-_(aq) →

What happens if you leave this precipitate in air???

Fe(OH)₂(s), green precipitate

Fe(OH)_2(s) → Fe(OH)_3(s), orange-brown precipitate

Redox reaction equation:

MnO₄^- → Mn²⁺

Fe²⁺ → Fe³⁺

MnO₄^-_(aq) + 8H⁺_(aq) + 5Fe²⁺_(aq) → Mn²⁺_(aq) + 5Fe³⁺_(aq) + 4H₂O_(l)

purple colourless

if in acid conditions, redox can be balanced with…

H₂O / H⁺

if in alkaline conditions, redox can be balanced with…

H₂O / OH^-

Full redox equation → acidic conditions

Cr₂O₇^-_(aq) → Cr³⁺_(aq)

Zn_(s) → Zn²⁺

Cr₂O₇^2-_(aq) + 14H⁺_(aq) + 3Zn_(s) → 2Cr³⁺_(aq) + 7H₂O_(l) + 3Zn²⁺_(aq)

with an excess of zinc, chromium (III) ions are reduced further to..

chromium (II) → pale blue colour

Zn_(s) + 2Cr³⁺_(aq) → Zn²⁺_(aq) + 2Cr²⁺_(aq)

Oxidation of Cr³⁺ → CrO₄^2- with H₂O₂

3H₂O₂ + 2Cr³⁺+ 10OH^- → 2CrO₄^2- + 8H₂O

When aqueous copper (II) ions, Cu²⁺, react with excess iodide ions, I^-_(aq) a redox reaction occurs. I^- is oxidised to brown iodine, I₂. Cu²⁺is reduced to Cu⁺

Disproportionation of Cu⁺ ions in Cu₂O_(s) + H₂SO_4(aq)

Cu₂O_(s) + H₂SO_4(aq) → Cu_(s) + CuSO_4(aq) + H₂O_(l)

……………………… reduction oxidation

test for ammonium ions + equation!

NaOH heated gently with the solution. Damp red pH indicator paper turns blue.

NH₄⁺_(aq) + OH^-_(aq) → NH_3(g) + H₂O_(l)