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AN INTRODUCTION TO TRANSITION METAL CHEMISTRY. 2008 SPECIFICATIONS. KNOCKHARDY PUBLISHING. KNOCKHARDY PUBLISHING. TRANSITION METALS. INTRODUCTION

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slide1

AN INTRODUCTION TO

TRANSITION METAL

CHEMISTRY

2008 SPECIFICATIONS

KNOCKHARDY PUBLISHING

slide2

KNOCKHARDY PUBLISHING

TRANSITION METALS

INTRODUCTION

This Powerpoint show is one of several produced to help students understand selected topics at AS and A2 level Chemistry. It is based on the requirements of the AQA and OCR specifications but is suitable for other examination boards.

Individual students may use the material at home for revision purposes or it may be used for classroom teaching if an interactive white board is available.

Accompanying notes on this, and the full range of AS and A2 topics, are available from the KNOCKHARDY SCIENCE WEBSITE at...

www.knockhardy.org.uk/sci.htm

Navigation is achieved by...

either clicking on the grey arrows at the foot of each page

or using the left and right arrow keys on the keyboard

slide3

TRANSITION METALS

  • CONTENTS
  • Definition
  • Metallic properties
  • Electronic configurations
  • Variable oxidation state
  • Coloured ions
  • Complex ion formation
  • Shapes of complexes
  • Isomerism in complexes
  • Catalytic properties
slide4

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
slide5

THE FIRST ROW TRANSITION ELEMENTS

DefinitionD-block elements forming one or more stable ions with

partially 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

slide6

THE FIRST ROW TRANSITION ELEMENTS

DefinitionD-block elements forming one or more stable ions with

partially 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

Metallic

properties 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

slide7

4f

4d

4

4p

ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS

POTASSIUM

INCREASING ENERGY / DISTANCE FROM NUCLEUS

3d

4s

3

3p

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

‘Aufbau’ Principle

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.

slide8

4f

4d

4

4p

ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS

CALCIUM

INCREASING ENERGY / DISTANCE FROM NUCLEUS

3d

4s

3

3p

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.

slide9

4f

4d

4

4p

ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS

SCANDIUM

INCREASING ENERGY / DISTANCE FROM NUCLEUS

3d

4s

3

3p

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.

slide10

4f

4d

4

4p

ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS

TITANIUM

INCREASING ENERGY / DISTANCE FROM NUCLEUS

3d

4s

3

3p

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 OF

MAXIMUM MULTIPLICITY

slide11

4f

4d

4

4p

ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS

VANADIUM

INCREASING ENERGY / DISTANCE FROM NUCLEUS

3d

4s

3

3p

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.

HUND’S RULE OF

MAXIMUM MULTIPLICITY

slide12

4f

4d

4

4p

ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS

CHROMIUM

INCREASING ENERGY / DISTANCE FROM NUCLEUS

3d

4s

3

3p

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.

slide13

4f

4d

4

4p

ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS

MANGANESE

INCREASING ENERGY / DISTANCE FROM NUCLEUS

3d

4s

3

3p

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

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

slide14

4f

4d

4

4p

ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS

IRON

INCREASING ENERGY / DISTANCE FROM NUCLEUS

3d

4s

3

3p

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

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

HUND’S RULE OF

MAXIMUM MULTIPLICITY

slide15

4f

4d

4

4p

ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS

COBALT

INCREASING ENERGY / DISTANCE FROM NUCLEUS

3d

4s

3

3p

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

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

HUND’S RULE OF

MAXIMUM MULTIPLICITY

slide16

4f

4d

4

4p

ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS

NICKEL

INCREASING ENERGY / DISTANCE FROM NUCLEUS

3d

4s

3

3p

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

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

HUND’S RULE OF

MAXIMUM MULTIPLICITY

slide17

4f

4d

4

4p

ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS

COPPER

INCREASING ENERGY / DISTANCE FROM NUCLEUS

3d

4s

3

3p

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.

HUND’S RULE OF

MAXIMUM MULTIPLICITY

slide18

4f

4d

4

4p

ELECTRONIC CONFIGURATIONS OF THE FIRST ROW TRANSITION METALS

ZINC

INCREASING ENERGY / DISTANCE FROM NUCLEUS

3d

4s

3

3p

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.

slide19

ELECTRONIC CONFIGURATIONS

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

slide20

Sc

Ti

V

Cr

Mn

Fe

Co

Ni

Cu

Zn

+7

+6

+6

+6

+5

+5

+5

+5

+5

+4

+4

+4

+4

+4

+4

+4

+3

+3

+3

+3

+3

+3

+3

+3

+2

+2

+2

+2

+2

+2

+2

+2

+2

+1

VARIABLE OXIDATION STATES

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

maximum rises across row to manganese

maximum falls as the energy required to

remove more electrons becomes very high

all (except scandium) have an M2+ ion

stability of +2 state increases across the row

due to increase in the 3rd Ionisation Energy

THE MOST IMPORTANT STATES ARE IN RED

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

Cu 1s2 2s2 2p6 3s2 3p63d10 4s1 Ti 1s2 2s2 2p6 3s2 3p63d2 4s2

Cu+ 1s2 2s2 2p6 3s2 3p63d10Ti2+ 1s2 2s2 2p6 3s2 3p63d2

Cu2+ 1s2 2s2 2p6 3s2 3p63d9 Ti3+ 1s2 2s 2p6 3s2 3p63d1 Ti4+ 1s2 2s2 2p6 3s23p6

slide21

COLOURED IONS

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

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 colourless

e.g. titanium(IV) oxide TiO2 is white

colour depends on ... transition element

oxidation state

ligand

coordination number

slide22

3d ORBITALS

There are 5 different orbitals of the d variety

xy

xz

yz

x2-y2

z2

slide23

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 theCENTRAL ION and theLIGAND

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.

OCTAHEDRAL

TETRAHEDRAL

3d

3d

slide24

COLOURED IONS

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

Absorbed colour nm Observed colour nm

VIOLET 400 GREEN-YELLOW 560

BLUE 450 YELLOW 600

BLUE-GREEN 490 RED 620

YELLOW-GREEN 570 VIOLET 410

YELLOW 580 DARK BLUE 430

ORANGE 600 BLUE 450

RED 650 GREEN 520

slide25

COLOURED IONS

a solution of copper(II)sulphate is blue because

red and yellow wavelengths are absorbed

blue and green not absorbed

white light

slide26

COLOURED IONS

a solution of copper(II)sulphate is blue because

red and yellow wavelengths are absorbed

slide27

COLOURED IONS

a solution of copper(II)sulphate is blue because

red and yellow wavelengths are absorbed

slide28

COLOURED IONS

a solution of nickel(II)sulphate is green because

violet, blue and red wavelengths are absorbed

slide29

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

RED LIGHT

WHITE LIGHT

COLORIMETER

BLUE FILTER

SOLUTION

slide30

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+

slide31

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 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.

slide32

COMPLEX IONS - LIGANDS

Formationligands form co-ordinate bonds to a central transition metal ion

Ligandsatoms, or ions, which possess lone pairs of electrons

form co-ordinate bonds to the central ion

donate a lone pair into vacant orbitals on the central species

Ligand Formula Name of ligand

chloride Cl¯ chloro

cyanide NC¯ cyano

hydroxide HO¯ hydroxo

oxide O2- oxo

water H2O aqua

ammonia NH3 ammine

some ligands attach themselves using two or more lone pairs

classified by the number of lone pairs they use

multidentate and bidentate ligands lead to more stable complexes

slide33

COMPLEX IONS - LIGANDS

some ligands attach themselves using two or more lone pairs

classified by the number of lone pairs they use

multidentate 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-

slide34

COMPLEX IONS - LIGANDS

some ligands attach themselves using two or more lone pairs

classified by the number of lone pairs they use

multidentate and bidentate ligands lead to more stable complexes

Multidentate form several co-ordinate bonds

EDTA

An important complexing agent

slide35

COMPLEX IONS - LIGANDS

some ligands attach themselves using two or more lone pairs

classified by the number of lone pairs they use

multidentate and bidentate ligands lead to more stable complexes

Multidentate form several co-ordinate bonds

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

slide36

COMPLEX IONS - LIGANDS

some ligands attach themselves using two or more lone pairs

classified by the number of lone pairs they use

multidentate and bidentate ligands lead to more stable complexes

Multidentate form several co-ordinate bonds

slide37

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]+

slide38

ISOMERISATION IN COMPLEXES

Some octahedral complexes can exist in more than one form

[MA4B2]n+

TRANS

CIS

[MA3B3]n+

slide39

ISOMERISATION IN COMPLEXES

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.

slide40

ISOMERISATION IN COMPLEXES

OPTICAL ISOMERISM

Some octahedral complexes exist in two forms

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

slide41

ISOMERISATION IN COMPLEXES

OPTICAL ISOMERISM AND GEOMETRICAL ISOMERSIM

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

OPTICAL ISOMERISM

slide42

ISOMERISATION IN COMPLEXES

OPTICAL ISOMERISM AND GEOMETRICAL ISOMERSIM

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

OPTICAL ISOMERISM

GEOMETRICAL ISOMERISM

CIS

TRANS

slide43

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

slide44

AN INTRODUCTION TO

TRANSITION METAL

CHEMISTRY

THE END

© 2009 JONATHAN HOPTON & KNOCKHARDY PUBLISHING