Boardworks GCSE Additional Science: Chemistry The Transition Metals

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What are the transition elements?

The transition elements are d-block elements which form one or more stable ions with incomplete d sub-shell electrons.

A transition element forms at least one ion with a partially-filled d-subshell

Ac Rf Db Sg Bh Hs Mt Ds Rg

La Hf Ta W Re Os Ir Pt Au Hg

Y Zr Nb Mo Tc Ru Rh Pd Ag Cd

Sc Ti V Cr Mn Fe Co Ni Cu Zn

?

Here, the word ‘transition’ is used to mean ‘in-between’.

group 2 group 3


Uses of coloured trans. metal compounds

The coloured compounds of transition metals can also be used in many ways, for example:

as coloured glazes on pottery.

to colour paints

to colour stained glass windows


What are the uses of the transition metals?


Prentice-Hall © 2002

General Chemistry: Chapter 24

Slide 6 of 47

Catalysis

• Catalysis plays an essential aspect in about 90% of all chemical manufacturing.

• Ni and Pt are very heterogeneous catalysts.

• Pt, Rh, and Pd are used in catalytic converters.

• V2O5 is used in conversion of SO2 to SO3.• Polyethylene is formed catalytically.


First row d-block elements

Elements Atomic num. Electronic Configuration[Ar] …

Sc 21 [Ar] 3d1 4s2Ti 22V 23Cr 24Mn 25Fe 26Co 27Ni 28Cu 29Zn 30


Most common oxidation state

Elements Electronic Configuration

Known oxidation state

Sc [Ar] 3d1 4s2 +3Ti [Ar] 3d2 4s2 +3, +4V [Ar] 3d3 4s2 +2, +3, +4, +5Cr [Ar] 3d5 4s1 +3, +6Mn [Ar]3d5 4s2 +2, +4, +6, +7Fe [Ar] 3d6 4s2 +2, +3Co [Ar] 3d7 4s2 +2, +3Ni [Ar] 3d8 4s2 +2Cu [Ar] 3d10 4s1 +1, +2Zn [Ar] 3d10 4s2 +2


Write the electron configuration of

•Cr3+

•Cu2+


exercise

• Explain why scandium (III) and zinc (II) cations are not called transition elements.

• Why is the maximum oxidation state of manganese +7?

• In the higher oxidation states, the elements exist as covalently bonded oxo-compounds rather than atomic ions. Explain this phenomenon


Characteristic of transitional metals on their compounds

• Variable oxidation stateDue to similar energy of 4s and 3d

• Formation of coloured ions / complex ionsDue to electrons transition between d-orbitals

• Catalytic activityProvide alternative reaction mechanism with

lower activation energy• Paramagnetism

Unpaired or odd electrons


The transition metals are known as ‘typical’ metals because of their physical properties. They are:

What are the properties of the transition metals?

lustrous (bright and shiny).

high density.

good conductors of heat and electricity.

high melting and boiling points (except mercury, which is liquid at room temperature).

hard and strong.

malleable (can be bent and pressed into different shapes) and ductile (can be drawn into wires).




Slide 13 of 47

Color and Magnetism


Comparing properties of different metals

How do the properties of transition metals compare with those of alkali metals?

are more dense. This means that in a fixed volume of metal there are more atoms of a transition metal than there are of an alkali metal.

have higher melting and boiling points – except mercury.

are harder and stronger. They cannot be cut with a knife.

Compared to the alkali metals, the transition metals:


Comparing densities of metals


Comparing melting points of metals


True or false?


Redox reactions

• A positive Ecell indicates a thermodynamically feasible reaction

• A negative Ecell indicates a thermodynamically non-feasible reaction


• Judging from Ecell [ data booklet ]oPredict the outcome of mixing aqueous

iron(II) with chlorine.oPredict the outcome of mixing acidified

tin (II) with hydrogen peroxide (H2O2)oWhich one is the better oxidising agent

in acidified solution : KMnO4 or K2Cr2O7

to oxidized solution of iron(II)


Complex ions

• A compound in which ligand molecules form (dative) co-ordinate bonds to a centre metal atom or ion.

• Ligand :a ion or molecule that has at least a lone pair of electrons available for donation to the central metal atom or ion.


How to write a complex structure


Features of complex ions

• Net charge on complex ions

Knowing the charge on a complex ion and the charge on each ligand, one can determine the

oxidation number for the metal.

Net charge

Ligand’s

Charge

Oxidation number



• In a compound, complex ion attaches to a counter ion.

K4[Fe(CN)6]

Na2CuCl4[Cu(NH3)4]SO4



• Co-ordination number(number of dative bonds attached)


Ligands

• NeutralH2O, NH3, CO, amines, etc

• IonicCl-, CN-, etc


Types of ligands

• Based on number of dative bonds:oMonodentate [ one dative bond ]

oH2O, NH3, halide, CN-, CO

o Bidentate [ two dative bonds ]oEthylenediamine, oxalate ions

o Polydentate [ more than two dative bonds ]oEDTA (EthyleneDiamineTetraAcetate ion)


chelate• Bidentate or polydentate ligands that form

ring in a complex ion.– Ethane-1,2-diamine [“en”]– Ethanedioate ions [“ox”]– EDTA


Rule for naming complex ions

• Complex cation– Names of ligands are given first, then the

central ion with its oxidation state in brakets– Ligands are named in alphabetical order with

suitable prefix to indicate number of ligand present [di, tri, tetra, etc]

– The ligand and central ion are named without space

• Complex anion– Similar method, except central metal ion is

altered to end in -ate


Ligands H2O NH3 F- Cl- CN- SCN- OH-Name aqua ammine fluoro chloro cyano thiocyanate Hydroxo

Cationic complexes Anionic complexesTitanium Titanatevanadium VanadateManganese ManganateIron FerrateCopper Cuprate

These are strong ligands




Slide 32 of 55

Table 25.2 Some Common Monodentate Ligands.


Give names

• Cu(en)22+

• Fe(Ox)33-

• [Cu(H2O)6]2+

• [Cr(NH3)5Cl]2+

• [Fe(CN)6]4-

• [Fe(H2O)6]2+

• [Cu(H2O)6]SO4

• [Cr(NH3)5Cl]Cl2• K4[Fe(CN)6]

• [Fe(H2O)6](NO3)2




Slide 34 of 55

Ethylene Diamine


Copper complex in ligand substitution

add ammonia solution

Cu(H2O)62+ Co(NH3)4(H2O)2

2+

blue deep blue / violet

CuCl42- Cu(OH)2 yellow-green pale blue

Add NaOH or NH3 (aq)

Add conc

HCl


Substitution of ligands

• Ligands can be exchange in the complex ions.

Cu(H2O)62+ + 2OH- Cu(OH)2(H2O)4(s) + 2H2O

pale blueCu(OH)2(H2O)4(s) + 4NH3 [Cu(H2O)2(NH3)4]2+ +

2H2O + 2OH-

Deep blue




Slide 37 of 47

Metal Carbonyls


Shape of complex ions

Coordination number

Shape Hybridization Examples

2 Linear sp [CuCl2]-

4 Tetrahedral sp3 [CuCl4]-

4 Square planar

dsp2 [Ni(CN)4]2-

6 Octahedral sp3d2 [Fe(H2O)6]2+


Orbital d




Slide 40 of 47

Oxidation States


Colour of complexes

• Depends on:– The nature of the central metal ions– Oxidation state of the central metal ions– Types of ligands


Splitting of d orbitals


• The two d-orbitals [dx2-y2, and dz2] locate along axes causing a repulsion by the coming electron from the ligans, as to compare with the other d-orbitals [dxy, dyz, dxy] which locate in between axes having lower repulsion.

• This causes d-orbitals to separate into 2 different energy levels.




Slide 44 of 55

Octahedral Complex and d-Orbital Energies




Slide 45 of 55

Electron Configuration in d-Orbitals

Hund’s rule

Δ > Plow spin d4

Δ < P high spin d4

pairing energy considerations

ΔP


The effect of types of ligand


CN- > NO2- > en > py NH3 > EDTA4- > SCN- > H2O >

ONO- > ox2- > OH- > F- > SCN- > Cl- > Br- > I-

Large ΔStrong field ligands

Small ΔWeak field ligands


Transition between d-d* electron




Slide 51 of 55

Geometric Isomerism


conclusion

• A substance appears coloured when certain wavelength of white light is absobed. The complementary wavelength [white light minus the colour absobed] gives the colour of the substance

• Transition of electron(s) d-d* transition




Slide 53 of 55

Effect of Ligands on the Colors of Coordination Compounds


Homework

• Explain the term homogeneous and heterogeneous catalyst.

• Give examples and reactions for homogeneous and heterogeneous catalyst.

• Compare, qualitatively, the melting point, density, atomic radius, ionic radius, first ionization energy and conductivity of the transition elements with those of calcium as a typical s-block element.


Glossary (1/2)alloy – A mixture of a metal and at least one other element.

catalyst – A substance that increases the speed of a chemical reaction without being used up.

corrosion – Damage to a metal caused by a chemical or reaction such as rusting.

density – A measure of mass in a given volume. Often expressed in g/dm3.

ductile – The ability of metals to be drawn into wires.

lustrous – Bright and shiny.

malleable – Capable of being bent and pressed into a different shape.


Glossary (2/2)precipitate – A solid that forms in a solution as a result

of a physical or chemical reaction.

thermal decomposition – The process by which a substance is broken down into two or more products by heating it.

transition metal – An element located in the block between groups 2 and 3 of the periodic table.


Anagrams


Properties of transition metals


Multiple-choice quiz

Boardworks GCSE Additional Science: Chemistry The Transition Metals

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