Chapter 15: Transition Metals - PowerPoint Presentation

Slide1

Chapter 15: Transition Metals

15.1 General Properties of Transition Metals

15.2 Complex Formation and the Shape of Complex Ions

15.3 Coloured Ions

15.4 Variable Oxidation States of Transition Elements

15.5 CatalysisSlide2

15.1 General Properties of Transition Metals

Learning Objectives:

Recall the general properties of transition metals.

Explain these properties in terms of electronic structure.Slide3

Review: Electron Configuration

Write out the electron configurations for the Period 4 d-block elements (

Sc

to Zn). Use the noble gas abbreviation.

Sc

– [

Ar] 4s2 3d1Ti – [Ar] 4s2 3d2V – [Ar] 4s2 3d3Cr – [Ar] 4s1 3d5Mn – [Ar] 4s2 3d5

Fe – [

Ar

] 4s

2

3d

6

Co – [

Ar

] 4s

2

3d

7

Ni – [

Ar

] 4s

2

3d

8

Cu – [

Ar

] 4s

1

3d10

Zn – [

Ar

] 4s

2

3d

10Slide4

Review: Electronic Configurations of Ions

Write the electron configurations for the Sc

3+

, the V

2+

and the Cu2+

ions.Sc3+ [Ar] V2+ [Ar] 3d3Cu2+ [Ar] 3d9Remember:Always form positive ions.S-block electrons always lost first.Slide5

Transition Metals

Transition Metal

= a metal that can form one or more stable ions with a partially filled d-subshellSlide6

Scandium and Zinc are

NOT

transition metals

Scandium and Zinc are not considered transition metals, even though they are d-block metals, because they only form one stable ion Sc

3+

and Zn

2+ and neither of those ions contains a partially filled d-orbital.Sc3+ [Ar] (empty d-subshell)Zn2+ [Ar] 3d10 (full d-subshell)Slide7

Physical Properties (Metallic Properties)

Good conductors of heat and electricity

Hard

Strong

Shiny

High melting and boiling pointsSlide8

Low Reactivity

Physical properties and fairly low reactivity makes them very useful materials.

Examples:

Iron (and alloy steel) useful as a building material for high strength.

Copper for water pipes and electrical wires

Titanium for jet engine parts (withstands high temperatures)Slide9

Special chemical

p

roperties are caused by partially filled d-subshells

Variable Oxidation States

– the 4s and 3d energy levels are very close together, so different amounts of electrons can be lost using similar amounts of energy

Coloured

– transition metal ions are colouredCatalysis – they are good catalysts as can easily go between two stable ionsComplex FormationSlide10

15.2 Complex formation

Learning Objectives:

Describe the formation of complex ions.

Determine the shape of complex ions.

Draw structure of complex ions.

Determine the charge of complex ions.Slide11

Formation of Complex Ions

Complex ion

= a metal ion surrounded by

coordinately

bonded ligands.

Coordinate bond

(dative covalent bond) = a covalent bond in which both electrons in the shared pair come from the same atomLigand = an ion or molecule that donates a pair of electrons to a central metal ion.Slide12

Shape of Complex Ion

Coordination number determines the shape of a complex ion.

Coordination number

= the number of coordinate bonds to ligands in a complex ionSlide13

Transition metal ions commonly form octahedral complexes with small ligands (H

2

O, NH

3

).

Transition metal ions commonly form tetrahedral complexes with larger ligands (Cl

-) This is because fewer ligands fit around the central metal ion.Slide14

Multidentate ligands

Ligands that can only form one bond are called

unidentate

.

Some ligands can attach to the metal ion more than once.

These are called

multidentate ligands.They have multiple lone pairs that can be donated to the metal ion.Bidentate ligands = form two coordinate bonds with metal ionTridentate ligands = form threeTetradentate ligands = forms fourSlide15
Slide16

Oxidation States

The total oxidation state of the complex ion is placed outside square brackets (Example: [Cu(H

2

O)

6

]

2+ has a total charge of 2+).What is the charge of the metal ion in [Cu(H2O)6]2+ ?+2 = x + 0  x = +2  Cu2+ Total Oxidation State of Complex Ion

Oxidation State of the Metal Ion

Sum of Oxidation States of LigandsSlide17

Examples of Complex Ions (that you need to know)

Cis-

platin

[Pt(NH

3

)

2Cl2]Tollen’s reagent [Ag(NH3)2]+Haemoglobin Slide18

Cis-platin

[Pt(NH

3

)

2

Cl

2]Square planar shapeCis (The chlorines are on the same side)Successful anti-cancer drugTrans-platin interestingly has no anti-cancer properties.Slide19

Tollen’s Reagent

Contains complex ion [Ag(NH

3

)

2

]

+Linear shape.Distinguishes between aldehydes and ketones.Aldehydes reduce ion to Ag (silver mirror). Slide20

Haemaglobin

Contains a

Fe

2+

ion which are hexa-coordinated (

6 coordinate bonds

).Four coordinate bonds are from nitrogens on the tetradentate ligand called porphyrin.The section containing the Fe2+ surrounded by the nitrogen porphyrin ring is called “haem”.A fifth nitrogen is attached to a larger protein called “globin”.What is the sixth bond?Slide21

Haemoglobin

The sixth bond is with water or

oxygen

.

This is how oxygen is carried around the body through the blood.

O

2 is not a very good ligand (weak bond with Fe2+) so easily given up to cells.However, CO binds irreversible (forms stable complex) and destroys haemoglobin’s ability to carry oxygen.Slide22

15.3 Coloured Ions

Learning Objectives:

Describe the factors that determine the colour of a complex ion.

Link the colour to electronic configuration.Slide23
Slide24

Why are transition metal ions coloured?

Part filled d-orbitals

Possible for electrons to move from one d-orbital to another.

Compounds have d-orbitals of slightly different energy levels.

Electrons absorb energy and move up to a higher energy level.

Wavelength of the energy is equal to the difference in energy.

This wavelength of light is removed and the other colours are reflected (the colour you see).Slide25

Amount of energy

Δ

E = h

ν

Δ

E : amount of energy h = Planck’s constant ν = frequency of light absorbedSlide26

What colour?

Large energy gap

 Higher frequency of light 

Violet

absorbed

Complementary colour reflected:

Appears YellowSmall energy gap  Lower frequency  Red is absorbedComplementary colour reflected:Appears GreenSlide27

What affects the colour?

Metal Ion

Oxidation State

Coordination number

LigandsSlide28

Spectrometry

can be used to determine the concentration of a solution by measuring how much light it absorbs.

Filter

is used to only allow through the colour of light absorbed by the substance being tested.

A

colorimeter

detects how much light has been absorbed and the concentration of the sample can be calculated.Slide29

Calibration graph

Solutions of known concentration are tested.

The results are plotted on a calibration graph.

The concentration of the unknown sample can then be predicted using the calibration graph.Slide30

15.4 Variable Oxidation States

Learning Objectives:

Recall that transition elements have variable oxidation states.

Recall the equilibrium reaction between chromium, chromate (VI) ions and dichromate(VI) ions.

Recall the oxidation reaction of Co

2+

and Cr3+ ions by water.Recall the oxidation of Co2+ ions by air.Represent these equations using half equations.Slide31

Redox of Transition Elements

Transition elements commonly undergo redox reactions as they have more than one stable ion.

Example:

Write out the half equation for Fe

2+

ions reacting with Cl

2 gas to form Fe3+ ions and Cl- ions.Write out the balanced redox reaction.What is oxidised? What is reduced?What is the oxidising agent? What is the reducing agent?Slide32

Half Equations

Fe

2+

 Fe

3+

+ e

-Cl2 + 2e-  2Cl-Balanced Redox Equation2Fe2+ (aq) + Cl2

(g)

 2Fe

3+

(

aq

)

+ 2Cl

-

(

aq

)

Fe

2+

is oxidised (+2  +3), Cl

2

is reduced (0-1)

Cl

2

is the oxidising agent and Fe

2+

is the reducing agent.Slide33

Potassium

manganate

(VII)

can act as an

oxidising agent

in

acidic conditions (H+ aqueous).KMnO4MnO4- is reduced to Mn2+Write the balanced redox equation for Fe2+ being oxidised to Fe3+ by potassium manganite (VII) in acidic conditions.Slide34

Potassium manganite (VII) is soluble so forms K+ and MnO4- ions.

MnO

4

-

+ 5e

-  Mn

2+ (+7  +2)MnO4- + 8H+ + 5e-  Mn2+ + 4H2OFe2+  Fe3+

+ e

-

(+2  +3)

5Fe

2+

 5Fe

3+

+ 5e

-

MnO

4

-

+ 5Fe

2+

+ 8H

+

 Mn

2+

+ 5Fe

3+

+ 4H

2

OSlide35

Redox Titrations

Redox reactions can be used instead of neutralisation reactions in a titration to determine the concentration of an oxidising or reducing agent in solution.

Acidified potassium

manganate

(VII)

(

oxidising agent) can be used to react with a reducing agent to determine it’s concentration.Potassium manganate(VII) is deep purple and is used to self indicate as the purple colour disappears when the ions are reduced.If the purple colour remains, that means that all the reducing agent has been oxidised (leaving leftover oxidising agent).Slide36

Chromium ions

Oxidation State

Formula

of Ion

Colour

Stable In

+6Cr2O72-(dichromate)OrangeAcid+6CrO42-(chromate)Yellow

Alkali

+3

Cr

3+

Green/Violet

+2

Cr

2+

BlueSlide37

Reactions with Chromium Ions