AN INTRODUCTION TO TRANSITION METAL CHEMISTRY KNOCKHARDY PUBLISHING 2008 SPECIFICATIONS.

AN INTRODUCTION TO

TRANSITION METALCHEMISTRY

KNOCKHARDY PUBLISHING2008

SPECIFICATIONS

INTRODUCTION

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KNOCKHARDY PUBLISHING

TRANSITION METALS

CONTENTS• Definition

• Metallic properties

• Electronic configurations

• Variable oxidation state

• Coloured ions

• Complex ion formation

• Shapes of complexes

• Isomerism in complexes

• Catalytic properties

TRANSITION METALS

Before you start it would be helpful to…

• Recall the definition of a co-ordinate (dative covalent) bond

• Recall how to predict the shapes of simple molecules and ions

TRANSITION METALS

THE FIRST ROW TRANSITION ELEMENTS

Definition D-block elements forming one or more stable ions withpartially filled (incomplete) d-sub shells.

The first row runs from scandium to zinc filling the 3d orbitals.

Properties arise from an incomplete d sub-shell in atoms or ions

THE FIRST ROW TRANSITION ELEMENTS

Definition D-block elements forming one or more stable ions withpartially filled (incomplete) d-sub shells.

The first row runs from scandium to zinc filling the 3d orbitals.

Properties arise from an incomplete d sub-shell in atoms or ions

Metallicproperties all the transition elements are metals

strong metallic bonds due to small ionic size and close packing higher melting, boiling points and densities than s-block metals

K Ca Sc Ti V Cr Mn Fe Co

m. pt / °C 63 850 1400 1677 1917 1903 1244 1539 1495

density /g cm-3 0.86 1.55 3 4.5 6.1 7.2 7.4 7.9 8.9

4s

3 3p

3d

44p

4d

4f

ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS

POTASSIUM

1s2 2s2 2p6 3s2 3p6 4s1

In numerical terms one would expect the 3d orbitals to be filled next.

However, because the principal energy levels get closer together as you go further from the nucleus coupled with the splitting into sub energy levels, the 4s orbital is of a LOWER ENERGY than the 3d orbitals so gets filled first.

‘Aufbau’ Principle‘Aufbau’ Principle

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4s

3 3p

3d

44p

4d

4f


CALCIUM

1s2 2s2 2p6 3s2 3p6 4s2

As expected, the next electron in pairs up to complete a filled 4s orbital.

This explanation, using sub levels fits in with the position of potassium and calcium in the Periodic Table. All elements with an -s1 electronic configuration are in Group I and all with an -s2 configuration are in Group II.

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4s

3 3p

3d

44p

4d

4f


SCANDIUM

1s2 2s2 2p6 3s2 3p6 4s2 3d1

With the lower energy 4s orbital filled, the next electrons can now fill p the 3d orbitals. There are five d orbitals. They are filled according to Hund’s Rule.

BUT WATCH OUT FOR TWO SPECIAL CASES.

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4s

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44p

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TITANIUM

1s2 2s2 2p6 3s2 3p6 4s2 3d2

The 3d orbitals are filled according to Hund’s rule so the next electron doesn’t pair up but goes into an empty orbital in the same sub level.

HUND’S RULE OFMAXIMUM MULTIPLICITY


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4s

3 3p

3d

44p

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VANADIUM

1s2 2s2 2p6 3s2 3p6 4s2 3d3

The 3d orbitals are filled according to Hund’s rule so the next electron doesn’t pair up but goes into an empty orbital in the same sub level.



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4s

3 3p

3d

44p

4d

4fIN

CR

EA

SIN

G E

NE

RG

Y /

D

ISTA

NC

E F

RO

M

NU

CL

EU

S


CHROMIUM

1s2 2s2 2p6 3s2 3p6 4s1 3d5

One would expect the configuration of chromium atoms to end in 4s2 3d4.

To achieve a more stable arrangement of lower energy, one of the 4s electrons is promoted into the 3d to give six unpaired electrons with lower repulsion.

4s

3 3p

3d

44p

4d

4f


MANGANESE

1s2 2s2 2p6 3s2 3p6 4s2 3d5

The new electron goes into the 4s to restore its filled state.

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4s

3 3p

3d

44p

4d

4f


IRON

1s2 2s2 2p6 3s2 3p6 4s2 3d6

Orbitals are filled according to Hund’s Rule. They continue to pair up.



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4s

3 3p

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44p

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COBALT

1s2 2s2 2p6 3s2 3p6 4s2 3d7




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4s

3 3p

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44p

4d

4f


NICKEL

1s2 2s2 2p6 3s2 3p6 4s2 3d8




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4s

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COPPER

1s2 2s2 2p6 3s2 3p6 4s1 3d10

One would expect the configuration of copper atoms to end in 4s2 3d9.

To achieve a more stable arrangement of lower energy, one of the 4s electrons is promoted into the 3d.



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4s

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ZINC

1s2 2s2 2p6 3s2 3p6 4s2 3d10

The electron goes into the 4s to restore its filled state and complete the 3d and 4s orbital filling.

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K 1s2 2s2 2p6 3s2 3p6 4s1

Ca 1s2 2s2 2p6 3s2 3p6 4s2

Sc 1s2 2s2 2p6 3s2 3p6 4s2 3d1

Ti 1s2 2s2 2p6 3s2 3p6 4s2 3d2

V 1s2 2s2 2p6 3s2 3p6 4s2 3d3

Cr 1s2 2s2 2p6 3s2 3p6 4s1 3d5

Mn 1s2 2s2 2p6 3s2 3p6 4s2 3d5

Fe 1s2 2s2 2p6 3s2 3p6 4s2 3d6

Co 1s2 2s2 2p6 3s2 3p6 4s2 3d7

Ni 1s2 2s2 2p6 3s2 3p6 4s2 3d8

Cu 1s2 2s2 2p6 3s2 3p6 4s1 3d10

Zn 1s2 2s2 2p6 3s2 3p6 4s2 3d10

ELECTRONIC CONFIGURATIONS

VARIABLE OXIDATION STATES

Arises from the similar energies required for removal of 4s and 3d electrons

When electrons are removed they come from the 4s orbitals first

Cu 1s2 2s2 2p6 3s2 3p6 3d10 4s1 Ti 1s2 2s2 2p6 3s2 3p6 3d2 4s2

Cu+ 1s2 2s2 2p6 3s2 3p6 3d10 Ti2+ 1s2 2s2 2p6 3s2 3p6 3d2

Cu2+ 1s2 2s2 2p6 3s2 3p6 3d9 Ti3+ 1s2 2s 2p6 3s2 3p6 3d1

Ti4+ 1s2 2s2 2p6 3s2 3p6

maximum rises across row to manganese

maximum falls as the energy required toremove more electrons becomes very high

all (except scandium) have an M2+ ion

stability of +2 state increases across the rowdue to increase in the 3rd Ionisation Energy

THE MOST IMPORTANT STATES ARE IN RED

Ti Sc V Cr Mn Fe Co Ni Cu Zn

+1

+2

+3

+4

+5

+6

+2 +2 +2 +2 +2 +2 +2 +2

+6

+7

+3+3 +3

+4

+3

+4

+3 +3 +3

+4 +4 +4 +4

+5 +5 +5 +5

+6

COLOURED IONS

Theory ions with a d10 (full) or d0 (empty) configuration are colourless

ions with partially filled d-orbitals tend to be coloured

it is caused by the ease of transition of electrons between energy levels

energy is absorbed when an electron is promoted to a higher level

the frequency of light is proportional to the energy difference

ions with d10 (full) Cu+,Ag+ Zn2+

or d0 (empty) Sc3+ configuration are colourlesse.g. titanium(IV) oxide TiO2 is white

colour depends on ... transition elementoxidation stateligandcoordination number

A characteristic of transition metals is their ability to form coloured compounds

3d ORBITALS

There are 5 different orbitals of the d variety

z2x2-y2

xy xz yz

SPLITTING OF 3d ORBITALS

Placing ligands around a central ion causes the energies of the d orbitals to change Some of the d orbitals gain energy and some lose energy In an octahedral complex, two (z2 and x2-y2) go higher and three go lower In a tetrahedral complex, three (xy, xz and yz) go higher and two go lower

Degree of splitting depends on the CENTRAL ION and the LIGAND

The energy difference between the levels affects how much energy is absorbed when an electron is promoted. The amount of energy governs the colour of light absorbed.

3d 3d

OCTAHEDRAL TETRAHEDRAL

COLOURED IONS

Absorbed colour nm Observed colour nmVIOLET 400 GREEN-YELLOW 560BLUE 450 YELLOW 600BLUE-GREEN 490 RED 620YELLOW-GREEN 570 VIOLET 410YELLOW 580 DARK BLUE 430ORANGE 600 BLUE 450RED 650 GREEN 520

The observed colour of a solution depends on the wavelengths absorbed

Copper sulphate solution appears blue because the energy absorbed corresponds to red and yellow wavelengths. Wavelengths corresponding to blue light aren’t absorbed.

WHITE LIGHT GOES IN

SOLUTION APPEARS BLUE

ENERGY CORRESPONDING TO THESE COLOURS IS ABSORBED

COLOURED IONS

a solution of copper(II)sulphate is blue becausered and yellow wavelengths are absorbed

white lightblue and green not absorbed

COLOURED IONS

a solution of copper(II)sulphate is blue becausered and yellow wavelengths are absorbed

COLOURED IONS

a solution of nickel(II)sulphate is green becauseviolet, blue and red wavelengths are absorbed

WHITE LIGHT

BLUE FILTER

RED LIGHT

SOLUTIONCOLORIMETER

FINDING COMPLEX ION FORMULAE USING COLORIMETRY

• a change of ligand can change the colour of a complex• this property can be used to find the formula of a complex ion• ight of a certain wavelength is passed through a solution• the greater the colour intensity, the greater the absorbance• the concentration of each species in the complex is altered• the mixture with the greatest absorbance identifies ratio of ligands and ions



Finding the formula of an iron(III) complex

White light is passed through a blue filter. The resulting red light is passed through mixtures of an aqueous iron(III) and potassium thiocyanate solution. Maximum absorbance occurs first when the ratio of Fe3+ and SCN¯ is 1:1.

This shows the complex has the formula [Fe(H2O)5SCN]2+



Finding the formula of an nickel(II) edta complex

Filtered light is passed through various mixtures of an aqueous solution of nickel(II) sulphate and edta solution.

The maximum absorbance occurs when the ratio of Ni2+ and edta is 1:1.

COMPLEX IONS - LIGANDS

Formation ligands form co-ordinate bonds to a central transition metal ion

Ligands atoms, or ions, which possess lone pairs of electronsform co-ordinate bonds to the central iondonate a lone pair into vacant orbitals on the central species

Ligand Formula Name of ligandchloride Cl¯ chlorocyanide NC¯ cyanohydroxide HO¯ hydroxooxide O2- oxowater H2O aqua

ammonia NH3 ammine

some ligands attach themselves using two or more lone pairsclassified by the number of lone pairs they usemultidentate and bidentate ligands lead to more stable complexes



Unidentate form one co-ordinate bond Cl¯, OH¯, CN¯, NH3, and H2O

Bidentate form two co-ordinate bonds H2NCH2CH2NH2 , C2O42-



Multidentate form several co-ordinate bonds

EDTA

An important complexing agent




HAEM

A complex containing iron(II) which is responsible for the red colour in blood and for the transport of oxygen by red blood cells.

Co-ordination of CO molecules interferes with the process

CO-ORDINATION NUMBER & SHAPE

the shape of a complex is governed by the number of ligands around the central ion the co-ordination number gives the number of ligands around the central ion a change of ligand can affect the co-ordination number

Co-ordination No. Shape Example(s)

6 Octahedral [Cu(H2O)6]2+

4 Tetrahedral [CuCl4]2-

Square planar Pt(NH3)2Cl2

2 Linear [Ag(NH3)2]+

ISOMERISATION IN COMPLEXES

Some octahedral complexes can exist in more than one form

[MA4B2]n+

[MA3B3]n+

TRANS CIS


GEOMETRICAL (CIS-TRANS) ISOMERISM

Square planar complexes of the form [MA2B2]n+ exist in two forms

trans platin cis platin

An important anti-cancer drug. It is a square planar, 4 co-ordinate complex of platinum.


Octahedral complexes with bidentate ligands can exist as a pair of enantiomers (optical isomers)

OPTICAL ISOMERISM

Some octahedral complexes exist in two forms


OPTICAL ISOMERISM

OPTICAL ISOMERISM AND GEOMETRICAL ISOMERSIM

The complex ion [Co(en)2Cl2]+ exhibits both types of isomerism


OPTICAL ISOMERISM

OPTICAL ISOMERISM AND GEOMETRICAL ISOMERSIM

The complex ion [Co(en)2Cl2]+ exhibits both types of isomerism

GEOMETRICAL ISOMERISM

CIS TRANS

CATALYTIC PROPERTIES

Transition metals and their compounds show great catalytic activity

It is due to partly filled d-orbitals which can be used to form bonds with adsorbed reactants which helps reactions take place more easily

Examples of catalysts

IRON Manufacture of ammonia - Haber Process

NICKEL Hydrogenation reactions - margarine manufacture

RHODIUM Catalytic converters

VANADIUM(V) OXIDE Manufacture of sulphuric acid - Contact Process

AN INTRODUCTION TO TRANSITION METAL CHEMISTRY KNOCKHARDY PUBLISHING 2008 SPECIFICATIONS.

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