Unsur blok D

d_block

The d-Block Elements

#Why we study the Transition MetalsTransition metals are found in natureRocks and minerals contain transition metalsThe color of many gemstones is due to the presence of transition metal ionsRubies are red due to CrSapphires are blue due to presence of Fe and Ti Many biomolecules contain transition metals that are involved in the functions of these biomoleculesVitamin B12 contains CoHemoglobin, myoglobin, and cytochrome C contain Fe

#Why we study the Transition MetalsTransition metals and their compounds have many useful applicationsFe is used to make steel and stainless steelTi is used to make lightweight alloysTransition metal compounds are used as pigmentsTiO2 = whitePbCrO4 = yellowFe4[Fe(CN)6]3 (prussian blue)= blueTransition metal compounds are used in many industrial processes

#Introductiond-block elements The elements of periodic table belonging to group 3 to 12 are known as d-Block elements. because in these elements last electron enters in d sub shell or d orbitallocate between the s-block and p-blockoccur in the fourth and subsequent periods of the Periodic Table

#

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period 4period 5period 6period 7d-block elements

#Transition elements are elements that contain an incomplete d sub-shell (i.e. d1 to d9) in at least one of the oxidation states of their compounds.

3d03d10Introduction

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How are d - Block Elements & Transition elements different?Not all d block elements are transition elements but all transition elements are d-block elementsNot all d block elements are transition elements because d block elements like Zinc have full d10 configuration in their ground state as well as in their common oxidation state which is not according to definition of transition elements.

#IntroductionSc and Zn are not transition elements becauseThey form compounds with only one oxidation state in which the d sub-shell are NOT incomplete.Sc Sc3+ 3d0Zn Zn2+ 3d10

#IntroductionCu

Cu+ 3d10 not transitional Cu2+ 3d9 transitional

#Group 7 Presentation

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Which of the d-block elements may not be regarded as the transition elements?Why Zn, Cd and Hg are not considered as transition elements.Copper atom has completely filled d orbital (3d10) in its ground state, yet it is transition element. WhySilver atom has completely filled d orbital (4d10) in its ground state, yet it is transition element. WhyWhy the very name transition given to the elements of d-block .

#Zn, Cd and Hg

Because they do not have vacant d-orbitals neither in the atomic state nor in any stable oxidation state.

Copper (Z = 29) can exhibit +2 oxidation state wherein it will have incompletely filled d-orbitals (3d), hence a transition element.

Silver (Z = 47) can exhibit +2 oxidation state wherein it will have incompletely filled d-orbitals (4d), hence a transition element.

The very name transition given to the elements of d-block is only because of their position between s and p block elements.

Answers

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The first transition seriesthe first horizontal row of the d-block elements

#Characteristics of transition elements(d-block metals vs s-block metals)Physical properties vary slightly with atomic number across the series (cf. s-block and p-block elements)Higher m.p./b.p./density/hardness than s-block elements of the same periods.Variable oxidation states(cf. fixed oxidation states of s-block metals)

#Characteristics of transition elements4. Formation of coloured compounds/ions(cf. colourless ions of s-block elements)5. Formation of complexes6. Catalytic properties

#The building up of electronic configurations of elements follow:Aufbau principleHunds rulePauli exclusion principleElectronic Configurations

#3d and 4s sub-shells are very close to each other in energy.Relative energy of electrons in sub-shells depends on the effective nuclear charge they experience.Electrons enter 4s sub-shell firstElectrons leave 4s sub-shell firstElectronic Configurations

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CuCu2+

Relative energy levels of orbitals in atom and in ion

#Valence electrons in the inner 3d orbitalsElectronic ConfigurationsExamples:The electronic configuration of scandium: 1s22s22p63s23p63d14s2The electronic configuration of zinc: 1s22s22p63s23p63d104s2

#ElementAtomic numberElectronic configurationScandiumTitaniumVanadiumChromiumManganeseIronCobaltNickelCopperZinc21222324252627282930[Ar] 3d 14s2[Ar] 3d 24s2[Ar] 3d 34s2[Ar] 3d 54s1[Ar] 3d 54s2[Ar] 3d 64s2[Ar] 3d 74s2[Ar] 3d 84s2[Ar] 3d 104s1[Ar] 3d 104s2

Electronic configurations of the first series of the d-block elements

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A half-filled or fully-filled d sub-shellhas extra stability

#d -Block Elements as MetalsPhysical properties of d-Block elements : good conductors of heat and electricityhard and strongmalleable and ductiled-Block elements are typical metals

#d -Block Elements as MetalsPhysical properties of d-Block elements:Exceptions : Mercurylow melting pointliquid at room temperature and pressurelustroushigh melting points and boiling points

#d -Block Elements as Metalsd-block elementsextremely useful as construction materialsstrong and unreactive

#d -Block Elements as Metalsused for construction and making machinery nowadaysabundanteasy to extractIron

cheap

#d -Block Elements as MetalsIroncorrodes easilyoften combined with other elements to form steelharder and more resistant to corrosion

#d -Block Elements as MetalsTitaniumused to make aircraft and space shuttlesexpensive Corrosion resistant, light, strong and withstand large temperature changes

#d -Block Elements as MetalsManganeseconfers hardness & wearing resistance to its alloyse.g. duralumin : alloy of Al with Mn/Mg/CuChromiumconfers inertness to stainless steel

#d -Block Elements as MetalsThe similar atomic radii of the transition metals facilitate the formation of substitutional alloysthe atoms of one element to replace those of another elementmodify their solid structures and physical properties

#Atomic Radii and Ionic RadiiTwo features can be observed:1.The d-block elements have smalleratomic radii than the s-block elements2.The atomic radii of the d-block elements do not show much variation across the series

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Variation in atomic radius of the first 36 elementsAtomic Radii and Ionic Radii

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#

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(i) Nuclear charge (ii) Shielding effect (repulsion between e-) (i) > (ii)

(i) (ii)

(ii) > (i)On moving across the Period,

#At the beginning of the seriesatomic number effective nuclear charge the electron clouds are pulled closer to the nucleusatomic size Atomic Radii and Ionic Radii

#In the middle of the seriesthe effective nuclear charge experienced by 4s electrons increases very slowlyonly a slow decrease in atomic radius in this regionmore electrons enter the inner3d sub-shellThe inner 3d electrons shield the outer 4s electrons effectively

#At the end of the seriesthe screening and repulsive effects of the electrons in the 3d sub-shell become even strongerAtomic size Atomic Radii and Ionic Radii

#Many of the differences in physical and chemical properties between the d-block and s-block elementsexplained in terms of their differences in electronic configurations and atomic radiiComparison of Some Physical and Chemical Properties between the d-Block and s-Block Elements

#1. Density

Densities (in g cm3) of the s-block elements and the first series of the d-block elements at 20C

#d-block > s-block the atoms of the d-block elements 1.are generally smaller in size 2.are more closely packed (fcc/hcp vs bcc in group 1)3. have higher relative atomic masses1. Density

#The densitiesgenerally increase across the first series of the d-block elements 1.general decrease in atomic radius across the series2.general increase in atomic mass across the series1. Density

#2. Ionization EnthalpyElementIonization enthalpy (kJ mol1)1st2nd3rd4thKCa4185903 0701 1504 6004 9405 8606 480ScTiVCr6326616486531 2401 3101 3701 5902 3902 7202 8702 9907 1104 1704 6004 770

K Ca (sharp ) ;Ca Sc (slight )

#2. Ionization EnthalpyElementIonization enthalpy (kJ mol1)1st2nd3rd4thCrMnFeCoNiCuZn6537167627577367459081 5901 5101 5601 6401 7501 9601 7302 9903 2502 9603 2303 3903 5503 8284 7705 1905 4005 1005 4005 6905 980

Sc Cu (slight ) ;Cu Zn (sharp )

#The first ionization enthalpies of thed-block elementsgreater than those of the s-block elements in the same period of the Periodic Table1. The atoms of the d-block elements are smaller in size2. greater effective nuclear charges2. Ionization Enthalpy

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Sharp across periods 1, 2 and 3Slight across the transition series

#Going across the first transition seriesthe nuclear charge of the elements increasesadditional electrons are added to the inner 3d sub-shell2. Ionization Enthalpy

#The screening effect of the additional3d electrons is significant2. Ionization EnthalpyThe effective nuclear charge experienced by the 4s electrons increases very slightly across the seriesFor 2nd, 3rd, 4th ionization enthalpies,slight and gradual across the series are observed.

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Electron has to be removed from completely filled 3p subshell3d53d53d53d10

d10/s2Cr+Mn2+Fe3+

#The first few successive ionization enthalpies for the d-block elementsdo not show dramatic changes 4s and 3d energy levels are close to each other2. Ionization Enthalpy

#3. Melting Points and Hardness

1541 1668 1910 1907 1246 1538 1495 1455 1084 419 d-block >> s-block 1. both 4s and 3d e- are involved in the formation of metal bonds 2. d-block atoms are smaller

#3. Melting Points and HardnessK has an exceptionally small m.p. because it has an more open b.c.c. structure.

1541 1668 1910 1907 1246 1538 1495 1455 1084 419

# Unpaired electrons are relatively more involved in the sea of electrons Sc Ti V Cr Mn Fe Co Ni Cu Zn1541 1668 1910 1907 1246 1538 1495 1455 1084 419

#

3d4sSc

Ti

Vm.p. from Sc to V due to the of unpaired d-electrons (from d1 to d3) Sc Ti V Cr Mn Fe Co Ni Cu Zn1541 1668 1910 1907 1246 1538 1495 1455 1084 419

#2.m.p. from Fe to Zn due to the of unpaired d-electrons (from 4 to 0) Sc Ti V Cr Mn Fe Co Ni Cu Zn1541 1668 1910 1907 1246 1538 1495 1455 1084 419

3d4sFe

Co

Ni

# Sc Ti V Cr Mn Fe Co Ni Cu Zn1541 1668 1910 1907 1246 1538 1495 1455 1084 419 3. Cr has the highest no. of unpaired electrons but its m.p. is lower than V.

3d4sCrIt is because the electrons in the half-filled d-subshell are relatively less involved in the sea of electrons.

# Sc Ti V Cr Mn Fe Co Ni Cu Zn1541 1668 1910 1907 1246 1538 1495 1455 1084 419 4.Mn has an exceptionally low m.p. because it has the very open cubic structure.Why is Hg a liquid at room conditions ?All 5d and 6s electrons are paired up and the size of the atoms is much larger than that of Zn.

#The metallic bonds of the d-block elements are stronger than those of the s-block elements much harder than the s-block elements3. Melting Points and HardnessThe hardness of a metal depends onthe strength of the metallic bonds

#Mohs scale : - A measure of hardnessTalc Diamond

010 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn 0.5 1.5 3.0 4.5 6.1 9.0 5.0 4.5 -- -- 2.8 2.5

#In general, the s-block elementsreact vigorously with water to form metal hydroxides and hydrogen4. Reaction with WaterThe d-block elementsreact very slowly with cold waterreact with steam to give metal oxides and hydrogen

#4. Reaction with Water2K(s) + 2H2O(l) 2KOH(aq) + H2(g)2Na(s) + 2H2O(l) 2NaOH(aq) + H2(g)Ca(s) + 2H2O(l) Ca(OH)2(aq) + H2(g)Zn(s) + H2O(g) ZnO(s) + H2(g)3Fe(s) + 4H2O(g) Fe3O4(s) + 4H2(g)

#d-block compounds vs s-block compoundsA Summary : -Ions of d-block metals have higher charge density more polarizing 1. more covalent in nature2. less soluble in water3. less basic (more acidic) Basicity : Fe(OH)3 < Fe(OH)2 Fe2+ > Na+

#d-block compounds vs s-block compoundsA Summary : - 4. less thermally stable e.g. CuCO3 Mn3+(aq) [Ar] 3d5 [Ar] 3d45.The relative stability of various oxidation states is correlated with the stability of electronic configurations

: Fe3+ > Fe2+

Major factor

Major factorFe3+(aq) > Fe2+(aq)[Ar] 3d5 [Ar] 3d6

#Stability : -Zn2+(aq) > Zn+(aq)[Ar] 3d10 [Ar] 3d104s15.The relative stability of various oxidation states is correlated with the stability of electronic configurations

: Zn2+ > Zn+

Major factor

#The compounds of vanadium, vanadiumoxidation states of +2, +3, +4 and +5forms ions of different oxidation statesshow distinctive colours in aqueous solutions1. Variable Oxidation States of Vanadium and their Interconversions

#IonOxidation state of vanadium in the ionColour in aqueous solutionV2+(aq)V3+(aq)VO2+(aq)VO2+(aq) +2+3+4+5VioletGreenBlueYellow

Colours of aqueous ions of vanadium of different oxidation states

#In an acidic mediumthe vanadium(V) state usually occurs in the form of VO2+(aq)dioxovanadium(V) ionthe vanadium(IV) state occurs in the form of VO2+(aq) oxovanadium(IV) ion1. Variable Oxidation States of Vanadium and their Interconversions

#In an alkaline mediumthe stable form of the vanadium(V) state is 1. Variable Oxidation States of Vanadium and their InterconversionsVO3(aq), metavanadate(V) or VO43(aq), orthovanadate(V), in strongly alkaline medium

#Compounds with vanadium in its highest oxidation state (i.e. +5)strong oxidizing agents1. Variable Oxidation States of Vanadium and their Interconversions

#Vanadium of its lowest oxidation state(i.e. +2)in the form of V2+(aq)strong reducing agenteasily oxidized when exposed to air1. Variable Oxidation States of Vanadium and their Interconversions

#The most convenient starting materialammonium metavanadate(V) (NH4VO3)a white solidthe oxidation state of vanadium is +51. Variable Oxidation States of Vanadium and their InterconversionsInterconversions of the common oxidation states of vanadium can be carried out readily in the laboratory

#1.Interconversions of Vanadium(V) species1. Variable Oxidation States of Vanadium and their InterconversionsVO2+(aq) V2O5(s) VO3(aq) VO43(aq)

OHH+

OHH+

OHH+ Yellow orange yellow colourlessVanadium(V) can exist as cation as well as anion


OHH+

OHH+

OHH+ Yellow orange yellow colourless

In acidic medium

In alkaline mediumAmphoteric


OHH+

OHH+


In acidic medium


Give the equation for the conversion : V2O5 VO2+V2O5(s) + 2H+(aq) 2VO2+(aq) + H2O(l)


OHH+

OHH+


In acidic medium


Give the equation for the conversion : V2O5 VO3V2O5(s) + 2OH(aq) 2VO3(aq) + H2O(l)


OHH+

OHH+


In acidic medium

In alkaline mediumGive the equation for the conversion : VO3 VO2+VO3(aq) + 2H+(aq) VO2+(aq) + H2O(l)Amphoteric

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VO43(aq) + 8H3O+

8H2O

V5+ ions does not exist in water since it undergoes vigorous hydrolysis to give VO43The reaction is favoured in highly alkaline solutionorthovanadate(V) ion

#V VO43(aq) orthovanadate(V) ionCr CrO42(aq) chromate(VI) ionMn MnO4(aq) manganate(VII) ionDraw the structures of VO43, CrO42 and MnO4

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VO3(aq) + 6H3O+

6H2O

The reaction is favoured in alkaline solutionVO3 is a polymeric anion like SiO32Metavanadate(V) ion

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Metavanadate(V) ion, (VO3)nn

#

VO2+(aq) + 4H3O+

4H2O

The reaction is favoured in acidic solution

#The action of zinc powder and concentrated hydrochloric acidvanadium(V) ions can be reduced sequentially to vanadium(II) ions1. Variable Oxidation States of Vanadium and their Interconversions

#1. Variable Oxidation States of Vanadium and their InterconversionsVO2+(aq) yellowZnconc. HClVO2+(aq) blueZnconc. HClV3+(aq) greenZnconc. HClV2+(aq) violet

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(a)Colours of aqueous solutions of compounds containing vanadium in four different oxidation states:(a) +5; (b) +4; (c) +3; (d) +2(b)(c)(d)VO2+(aq)VO2+(aq)V3+(aq)V2+(aq)

#The feasibility of the changes in oxidation state of vanadiumcan be predicted using standard electrode potentialsHalf reaction (V)Zn2+(aq) + 2eZn(s)VO2+(aq) + 2H+(aq) + eVO2+(aq) + H2O(l)VO2+(aq) + 2H+(aq) + eV3+(aq) + H2O(l)V3+(aq) + eV2+(aq)0.76+1.00+0.340.26

#Under standard conditionszinc can reduce 1.VO2+(aq) to VO2+(aq)1. Variable Oxidation States of Vanadium and their Interconversions

> 0

> 0

> 02.VO2+(aq) to V3+(aq)3.V3+(aq) to V2+(aq)

#1. Variable Oxidation States of Vanadium and their Interconversions2 (VO2+(aq) + 2H+(aq) + e VO2+(aq) + H2O(l)) = +1.00 V

)Zn2+(aq) + 2e Zn(s) = 0.76 V

2VO2+(aq) + Zn(s) + 4H+(aq)2VO2+(aq) + Zn2+(aq) + 2H2O(l) = +1.76 V

#1. Variable Oxidation States of Vanadium and their Interconversions2 (VO2+(aq) + 2H+(aq) + e V3+(aq) + H2O(l)) = +0.34 V

)Zn2+(aq) + 2e Zn(s) = 0.76 V

2VO2+(aq) + Zn(s) + 4H+(aq)2V3+(aq) + Zn2+(aq) + 2H2O(l) = +1.10 V

#1. Variable Oxidation States of Vanadium and their Interconversions2 (V3+(aq) + eV2+(aq)) = 0.26 V

)Zn2+(aq) + 2e Zn(s) = 0.76 V

2V3+(aq) + Zn(s)2V2+(aq) + Zn2+(aq) = +0.50 V

#Manganeseshow oxidation states of +2, +3, +4, +5, +6 and +7 in its compounds2. Variable Oxidation States of Manganese and their InterconversionsThe most common oxidation states+2, +4 and +7

#IonOxidation state of manganese in the ionColourMn2+Mn(OH)3Mn3+MnO2MnO43MnO42MnO4+2+3+3+4+5+6+7Very pale pinkDark brownRedBlackBright blueGreenPurple

Colours of compounds or ions of manganese in different oxidation states

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(a)Colours of compounds or ions of manganese in differernt oxidation states: (a) +2; (b) +3; (c) +4(b)(c)Mn2+(aq)Mn(OH)3(aq)MnO2(s)

#(e)(d)Colours of compounds or ions of manganese in differernt oxidation states: (d) +6; (e) +7

MnO42(aq)MnO4(aq)

#Manganese of the oxidation state +2the most stable at pH 02. Variable Oxidation States of Manganese and their InterconversionsMn2+Mn3+

+1.50VMn

1.18VMnO4

+1.51VMnO2

+1.23V

#Mn(VII)Explosive on heating and extremely oxidizing2KMnO4 K2MnO4 + MnO2 + O2

heat+7+6+420 in ON = 2(+2) = +4 in ON = (1) + (3) = 4

#Mn(VII) in ON = 6(+2) = +12 in ON = 4(3) = 1220+4+74MnO4 + 4H+ 4MnO2 + 2H2O + 3O2

lightThe reaction is catalyzed by lightAcidified KMnO4(aq) is stored in amber bottle

#Oxidizing power of Mn(VII) depends on pH of the solutionIn an acidic medium (pH 0)MnO4(aq) + 8H+(aq) + 5e Mn2+(aq) + 4H2O(l)

= +1.51 VIn a neutral or alkaline medium (up to pH 14)MnO4(aq) + 2H2O(l) + 3e MnO2(s) + 4OH (aq)

= +0.59 V

#The reaction does not involve H+(aq) nor OH(aq)Why is the Eo of MnO4 MnO42 Eo = +0.56Vnot affected by pH ?

MnO4(aq) + e MnO42 Eo = +0.56V

#MnO4(aq) + e MnO42 Eo = +0.56V

When [OH(aq)] > 1MIn an acidic medium (pH 0)MnO4(aq) + 8H+(aq) + 5e Mn2+(aq) + 4H2O(l)

= +1.51 VIn a neutral or alkaline medium (up to pH 14)MnO4(aq) + 2H2O(l) + 3e MnO2(s) + 4OH (aq)

= +0.59 VUnder what conditions is the following conversion favoured?

#Predict if Mn(VI) Mn(VII) + Mn(IV) is feasible at (i) pH 0 and (ii) pH 14

At pH 0 (1) 2(3)3MnO42(aq) + 4H+(aq) 2MnO4(aq) + MnO2(s) + 2H2O(l) Eocell = +1.70V (feasible)

At pH 14 (2) 2(3)3MnO42(aq) + 2H2O(l) 2MnO4(aq) + MnO2(s) + 4OH(aq) Eocell = +0.04V (much less feasible)

MnO42(aq) + 4H+(aq) + 2e MnO2(s) + 2H2O(l) Eo = +2.26V

MnO42(aq) + 2H2O(l) + 2e MnO2(s) + 4OH(aq) Eo = +0.60V

MnO4 + e MnO42 Eo = +0.56V

(1)(2)(3)Mn(VI) is unstable in acidic medium

#Mn(IV) Oxidizing in acidic mediumMnO2(s) + 4H+(aq) + 2e Mn2+(aq) + 2H2O(l)

= 1.23 VUsed in the laboratory production of chlorine MnO2(s) + 4HCl(aq) MnCl2(aq) + 2H2O(l) + Cl2(g)

#Mn(IV) Reducing in alkaline mediumOxidized to Mn(VI) in alkaline medium2MnO2 + 4OH + O2 2MnO42 + 2H2O

#MnO2 is oxidized to MnO42 in alkaline medium2MnO2 + 4OH + O2 2MnO42 + 2H2OSuggest a scheme to prepare MnO4 from MnO21. 2MnO2 + 4OH + O2 2MnO42 + 2H2O2. 3MnO42 + 4H+ 2MnO4 + MnO2 + 2H2O3. Filter the resulting mixture to remove MnO27B

#Cu+(aq) + e Cu(s) Eo = +0.52VCu2+(aq) + 2e Cu(s) Eo = +0.34VCu2+(aq) is more stable than Cu+(aq)The only copper(I) compounds which can be stable in water are those which are(i) insoluble (e.g. Cu2O, CuI, CuCl)(ii) complexed with ligands other than water e.g. [Cu(NH3)4]+Cu+(aq) + e Cu(s)Under these conditions, [Cu+(aq)] Equil. Position shifts to left

#Estimation of Cu2+ ions2Cu2+(aq) + 4I(aq) 2CuI(s) + I2(aq)I2(aq) + 2S2O32(aq) 2I(aq) + S4O62(aq)unknown excess white fixedstandard solution

#Another striking feature of the d-block elements is the formation of complexesFormation of Complexes

#Formation of ComplexesA complex is formed when a central metal atom or ion is surrounded by other molecules or ions which form dative covalent bonds with the central metal atom or ion.The molecules or ions that donate lone pairs of electrons to form the dative covalent bonds are called ligands.

#A ligandcan be an ion or a molecule having at least one lone pair of electrons that can be donated to the central metal atom or ion to form a dative covalent bondFormation of Complexes

#Formation of Complexeselectrically neutralNi(CO)4[Co(H2O)6]3+positively charged[Fe(CN)6]3negatively chargedComplexes can be

#A co-ordination compound is eithera neutral complex e.g. Ni(CO)4 or made of a complex ion and another ione.g.[Co(H2O)6]Cl3 [Co(H2O)6]3+ + 3Cl K3[Fe(CN)6] 3K+ + [Fe(CN)6]3

#Criteria for complex formation2.High charge density of the central metal ions.1.Presence of vacant and low-energy 3d, 4s, 4p and 4d orbitals in the metal atoms or ions to accept lone pairs from ligands.

#

Diagrammatic representation of the formation of a complex

#[Co(H2O)6]2+Co :

3d4s4p4dCo2+ :

3d4s4p4d

sp3d2 hybridisation

The six sp3d2 orbitals accept six lone pairs from six H2O. Arranged octahedrally to minimize repulsion between dative bonds.

#1. Complexes with Monodentate LigandsA ligand that forms one dative covalent bond only is called a monodentate ligand. Examples:neutral CO, H2O, NH3anionic Cl, CN, OH

#

#The transition metal ion is the Lewis acid since it accepts lone pairs of electrons from the ligands in forming dative covalent bonds. The ligand is the Lewis base since it donates a lone pair of electrons to the transition metal ion in forming dative covalent bonds. In the formation of complexes, classify the transition metal ion and the ligand as a Lewis acid or base. Explain your answer briefly.

#

What is the oxidation state of the central metal ?Cr3+Zn2+

#What is the oxidation state of the central metal ?

Co3+

#

What is the oxidation state of the central metal ?Fe3+Co2+

#2. Complexes with Bidentate LigandsA ligand that can form two dative covalent bonds with a metal atom or ion is called a bidentate ligand.A ligand that can form more than one dative covalent bond with a central metal atom or ion is called a chelating ligand.

#

Ethylenediamine (H2NCH2CH2NH2)Ethylenediamine (en)Oxalate (C2O42)oxalate ion (oxo)

The term chelate is derived from Greek, meaning claw.

The ligand binds with the metal like the great claw of the lobster.

#

ethylenediamineoxalate ion

#3. Complexes formed by Multidentate LigandsLigands that can form more than two dative covalent bonds to a metal atom or ion are called multidentate ligands. Some ligands can form as many as six bonds to a metal atom or ion. Example:ethylenediaminetetraacetic acid (abbreviated as EDTA)

#

ethylenediaminetetraacetate ion

EDTA forms six dative covalent bonds with the metal ion through six atoms giving a very stable complex. hexadentate ligand

#EDTA4Fe2+

[FeEDTA]2Structure of the complex ion formed by iron(II) ions and EDTA

?2

#Uses of EDTA1.Determining concentrations of metal ions by complexometric titrationse.g. determination of water hardness2.In chelation therapy for mercury poisoning and lead poisoningPoisonous Hg2+ and Pb2+ ions are removed by forming stable complexes with EDTA.3.Preparing buffer solutions ( )

4.As preservative to prevent catalytic oxidation of food by metal ions.

#The coordination number of the central metal atom or ion in a complex is the number of dative covalent bonds formed by the central metal atom or ion in a complex.ComplexThe central metal atom or ion in the complexCoordination number[Ag(NH3)2]+Ag+2[Cu(NH3)4]2+Cu2+4[Fe(CN)6]3 Fe3+6

#4. Nomenclature of Transition Metal Complexes with Monodentate LigandsIUPAC conventions1.(a)For any ionic compoundthe cation is named before the anion(b)If the complex is neutralthe name of the complex is the name of the compound

#1.(c)In naming a complex (which may be neutral, a cation or an anion)the ligands are named before the central metal atom or ionthe liqands are named in alphabetical order (prefixes not counted)(d)The number of each type of ligands are specified by the Greek prefixes1 mono-2 di3 tri4 tetra-5 penta-6 hexa-

#1.(e)The oxidation number of the metal ion in the complex is indicated immediately after the name of the metal using Roman numerals[CrCl2(H2O)4]Cltetraaquadichlorochromium(III) chloride[CoCl3(NH3)3]triamminetrichlorocobalt(III)K3[Fe(CN)6]potassium hexacyanoferrate(III)

#2.(a)The root names of anionic ligands always end in -oCNcyanoClchloroBrbromoIiodoOHhydroxoNO2nitroSO42sulphatoHhydrido(b)The names of neutral ligands are the names of the moleculesexcept NH3, H2O, CO and NO

#Neutral ligandName of ligandAmmonia (NH3)Water (H2O)Carbon monoxide (CO)Nitrogen monoxide (NO)AmmineAquaCarbonylNitrosyl

#3.(a)If the complex is anionicthe suffix -ate is added to the end of the name of the metal, followed by the oxidation number of that metaltetrachlorocuprate(II) ion[CuCl4]2hexacyanoferrate(III) ion[Fe(CN)6]3tetrachlorocobaltate(II) ion[CoCl4]2Name of the complexFormula

#MetalName in anionic complexTitaniumVanadiumChromiumManganeseIronCobaltNickelCopperZincPlatinumTitanateVanadateChromateManganateFerrateCobaltateNickelateCuprateZincatePlatinate

Names of some common metals in anionic complexes

#3.(b)If the complex is cationic or neutralthe name of the metal is unchanged followed by the oxidation number of that metaltriamminetrichlorocobalt(III)[CoCl3(NH3)3]tetraaquadichlorochromium(III) ion[CrCl2(H2O)4]+Name of the complexFormula

#(a)Write the names of the following compounds.(i) [Fe(H2O)6]Cl2(ii) [Cu(NH3)4]Cl2(iii) [PtCl4(NH3)2](iv) K2[CoCl4](v) [Cr(NH3)4SO4]NO3(vi) [Co(H2O)2(NH3)3Cl]Cl(vii) K3[AlF6]

#Hexaaquairon(II) chlorideTetraamminecopper(II) chlorideDiamminetetrachloroplatinum(IV)Potassium tetrachlorocobaltate(II)Tetraamminesulphatochromium(III) nitrate(i) [Fe(H2O)6]Cl2(ii) [Cu(NH3)4]Cl2(iii) [PtCl4(NH3)2](iv) K2[CoCl4](v) [Cr(NH3)4SO4]NO3

#(a) (vi) [Co(H2O)2(NH3)3Cl]Cl triamminediaquachlorocobalt(II) chloride (vii) K3[AlF6] potassium hexafluoroaluminate Al has a fixed oxidation state (+3) no need to indicate the oxidation state

#(b)Write the formulae of the following compounds.(i)pentaamminechlorocobalt(III) chloride

(ii)Ammonium hexachlorotitanate(IV)

(iii)Tetraaquadihydroxoiron(II)[Co(NH3)5Cl]Cl2(NH4)2[TiCl6][Fe(H2O)4(OH)2]

#Coordination number of the central metal atom or ionShape of complexExample2linear[Ag(NH3)2]+[Ag(CN)2]

Stereo-structures of complexes

sp hybridized

#[Cu(NH3)4]2+[CuCl4]2

Square planar[Zn(NH3)4]2+[CoCl4]2+

Tetrahedral4ExampleShape of complexCoordination number of the central metal atom or ion

Stereo-structures of complexessp3dsp2

#Tetra-coordinated Complexes

Tetrahedral complexestetrahedral shapeblue[Co(H2O)6]2+Octahedral, pink

#(b)Square planar complexeshave a square planar structure

Tetra-coordinated Complexes

#Example:

Tetra-coordinated Complexes

#Coordination number of the central metal atom or ionShape of complexExample6Octahedral[Cr(NH3)6]3+[Fe(CN)6]3

Stereo-structures of complexessp3d2

#Hexa-coordinated ComplexesExample:

#6. Displacement of Ligands and Relative Stability of Complex IonsDifferent ligands have different tendencies to bind with the metal atom/ionligands compete with one another for the metal atom/ion.A stronger ligand can displace a weaker ligand from a complex.

#6. Displacement of Ligands and Relative Stability of Complex Ions[Fe(H2O)6]2+(aq) + 6CN(aq)Hexaaquairon(II) ion [Fe(CN)6]4(aq) + 6H2O(l) Hexacyanoferrate(II) ion

Stronger ligandWeaker ligandReversible reactionEquilibrium position lies to the rightKst 1024 mol6 dm18

#[Ni(H2O)6]2+(aq) + 6NH3(aq)Hexaaquanickel(II) ion [Ni(NH3)6]2+(aq) + 6H2O(l)Hexaamminenickel(II) ion

Stronger ligandWeaker ligandThe greater the equilibrium constant,the stronger is the ligand on the LHS andthe more stable is the complex on the RHS

The equilibrium constant is called the stability constant, Kst

#Spectrochemical SeriesA partial spectrochemical series listing of ligands from small to large is given below. I < Br < S2 < SCN < Cl < NO3 < N3 < F < OH < C2O42 H2O < NCS < CH3CN < py (pyridine) < NH3 < en (ethylenediamine) < bipy (2,2'-bipyridine) < phen (1,10-phenanthroline) < NO2 < PPh3 < CN CO

#Consider the general equilibrium system below,[M(H2O)x]m+ + xLn [M(L)x](m-xn)+ + xH2O

Units = (mol dm3)-xKst measures the stability of the complex, [M(L)x](m-xn)+, relative to the aqua complex, [M(H2O)x]m+

#

Relative strength of some ligands bonding with copper(II) ions

monodentatebidentate

multidentate

TAS Expt 6

#EquilibriumKst ((mol dm3)n)[Cu(H2O)4]2+(aq) + 4Cl(aq)[CuCl4]2(aq) + 4H2O(l)[Cu(H2O)4]2+(aq) + 4NH3(aq)[Cu(NH3)4]2+(aq) + 4H2O(l)[Cu(H2O)4]2+(aq) + 2H2NCH2CH2NH2(aq) [Cu(H2NCH2CH2NH2)2]2+(aq) + 4H2O(l)[Cu(H2O)4]2+(aq) + EDTA4(aq)[CuEDTA]2(aq) + 4H2O(l)4.2 105

1.1 1013

1.0 1018.7

1.0 1018.8

What is the Kst of the formation of [Cu(H2O)4]2+(aq) ?

#[Cu(H2O)4]2+ + 4H2O [Cu(H2O)4]2+ + 4H2O

#Factors affecting the stability of complexesThe charge density of the central ion7.7 104

4.5 1033

[Co(H2O)6]2+(aq) + 6NH3(aq)[Co(NH3)6]2+(aq) + 6H2O(l)[Co(H2O)6]3+(aq) + 6NH3(aq)[Co(NH3)6]3+(aq) + 6H2O(l)Kst (mol6 dm18)Equilibrium

1024

1031[Fe(H2O)6]2+(aq) + 6CN(aq)[Fe(CN)6]4(aq) + 6H2O(l) [Fe(H2O)6]3+(aq) + 6CN(aq)[Fe(CN)6]3(aq) + 6H2O(l)

#Factors affecting the stability of complexes2.The nature of ligandsAbility to form complex : -CN > NH3 > Cl > H2O[Zn(CN)4]2Kst = 5 1016 mol4 dm12[Zn(NH3)4]2+Kst = 3.8 109 mol4 dm12[Cu(NH3)4]2+Kst = 1.1 1013 mol4 dm12[CuCl4]2+Kst = 4.2 105 mol4 dm12

#Factors affecting the stability of complexes3.The pH of the solutionIn acidic solution, the ligands are protonated lone pairs are not available the complex decomposes[Cu(NH3)4]2+(aq) + 4H2O(l) [Cu(H2O)4]2+(aq) + 4NH3(aq)

NH4+(aq)H+(aq)Equilibrium position shifts to the right

#Consider the stability constants of the following silver complexes:Ag+(aq) + 2Cl(aq) [AgCl2](aq) Kst = 1.1 105 mol2 dm6Ag+(aq) + 2NH3(aq) [Ag(NH3)2]+(aq) Kst = 1.6 107 mol2 dm6Ag+(aq) + 2CN(aq) [Ag(CN)2](aq) Kst = 1.0 1021 mol2 dm6

What will be formed when CN(aq) is added to a solution of [Ag(NH3)2]+?[Ag(CN)2](aq) and NH3

#What will be formed when NH3(aq) is added to a solution of [Ag(CN)2]? No apparent reactionConsider the stability constants of the following silver complexes:Ag+(aq) + 2Cl(aq) [AgCl2](aq) Kst = 1.1 105 mol2 dm6Ag+(aq) + 2NH3(aq) [Ag(NH3)2]+(aq) Kst = 1.6 107 mol2 dm6Ag+(aq) + 2CN(aq) [Ag(CN)2](aq) Kst = 1.0 1021 mol2 dm6

#Fe3+(aq) is too acidic.FeSO4(aq) is used as the antidote for cyanide poisoning[Fe(H2O)6]2+(aq) + 6CN(aq) [Fe(CN)6]4 + 6H2O(l)

Kst 1 1024 mol6 dm18

Very stable[Fe(H2O)6]3+(aq) + H2O(l) [Fe(H2O)5OH]2+(aq) + H3O+(aq)

Why is Fe2(SO4)3(aq) not used as the antidote ?Only free CN is poisonous

#[Cu(H2O)4]2+(aq) + Cl(aq) [Cu(H2O)3Cl]+(aq) + H2O(l)

K1 = 6.3102 mol1 dm3[Cu(H2O)3Cl]+(aq) + Cl(aq) [Cu(H2O)2Cl2](aq) + H2O(l)

K2 = 40 mol1 dm3[Cu(H2O)2Cl2](aq) + Cl(aq) [Cu(H2O)Cl3](aq) + H2O(l)

K3 = 5.4 mol1 dm3[Cu(H2O)Cl3](aq) + Cl(aq) [CuCl4]2(aq) + H2O(l)

K1 = 3.1 mol1 dm3[Cu(H2O)4]2+(aq) + 4Cl(aq) [CuCl4]2(aq) + 4H2O(l)

Kst = K1 K2 K3 K4 = 4.2 105 mol4 dm12

#K1 > K2 > K3 > K4Reasons :Statistical effectOn successive displacement, less water ligands are available to be displaced.

#K1 > K2 > K3 > K4Reasons :[Cu(H2O)Cl3] Cl

repulsion[Cu(H2O)4]2+ Cl

attraction2. Charge effectOn successive displacement, the Cl experiences more repulsion from the complex

#Formula of copper(II) complexColour of the complex[Cu(H2O)4]2+[CuCl4]2[Cu(NH3)4]2+[Cu(H2NCH2CH2NH2)]2+ [Cu(EDTA)]2 Pale blueYellowDeep blue VioletSky blue

Colours of some copper(II) complexesThe displacement of ligands are usually accompanied with easily observable colour changes

#

The colours of many gemstones are due to the presence of small quantities of d-block metal ionsColoured Ions

#Most of the d-block metalsform coloured compoundsColoured Ionsdue to the presence of the incompletely filled d orbitals in thed-block metal ions3d10 : Zn2+, Cu+; 3d0 : Sc3+, Ti4+Which aqueous transition metal ion(s) is/are not coloured ?

#Number of unpairedelectrons in 3d orbitalsd-Block metal ionColour inaqueous solution0Sc3+ Ti4+Zn2+Cu+ColourlessColourlessColourlessColourless1Ti3+V4+ Cu2+PurpleBlueBlue

Colours of some d-block metal ions in aqueous solutions

#Number of unpairedelectrons in 3d orbitalsd-Block metal ionColour inaqueous solution2V3+ Ni2+GreenGreen3V2+Cr3+ Co2+VioletGreenPink


#Number of unpairedelectrons in 3d orbitalsd-Block metal ionColour inaqueous solution4Cr2+Mn3+Fe2+BlueVioletGreen5Mn2+Fe3+Very pale pinkYellow


#Colours of some d-block metal ions in aqueous solutions

Co2+(aq)

Fe3+(aq)

Zn2+(aq)

#

Cu2+(aq)Fe2+(aq)

Mn2+(aq)Colours of some d-block metal ions in aqueous solutions

#A substance absorbs visible light of a certain wavelengthreflects or transmits visible light of other wavelengths (complimentary colour)appears colouredColoured ionLight absorbedLight reflected or transmitted[Cu(H2O)4]2+(aq)YellowBlue[CuCl4]2(aq)BlueYellow

#

BlueYellowMagentaGreenRedCyan

Violet

Greenish yellowComplimentary colour chartBlue light absorbedAppears yellowYellow light absorbedAppears blue

#The absorption of visible light is due to the d-d electronic transition3d 3di.e. an electron jumping from a lower 3d orbital to a higher 3d orbital Coloured Ions

#In gaseous state, the five 3d orbitals are degeneratei.e. they are of the same energy levelIn the presence of ligands,The five 3d orbitals interact with the orbitals of ligands and split into two groups of orbitals with slightly different energy levels

#The splitting of the degenerate 3d orbitals of a d-block metal ion in an octahedral complex

distributes along x and y axes

distributes along z axis

Interact more strongly with the orbitals of ligands

#

Higher energy eg

#Criterion for d-d transition : -presence of unpaired d electrons in the d-block metal atoms or ionsOr presence of incompletely filled d-subshelld-d transition is possible for 3d1 to 3d9 arrangementsd-d transition is NOT possible for 3d0 & 3d10 arrangements

#3d9 : d-d transition is possible

Cu2+H2O as ligand


*Cu2+Yellow light absorbed, appears blueH2O as ligand


Fe2+


*Fe2+Magenta light absorbed, appears green

#3d10 : d-d transition NOT possible

Zn2+

#3d0 : d-d transition NOT possible

Sc3+

#

EE depends on the nature and charge of metal ion[Fe(H2O)6]2+ green, [Fe(H2O)6]3+ yellow [Cu(H2O)4]2+ blue, [CuCl4]2 yellow 2.the nature of ligand

#Why does Na+(aq) appear colourless ?Coloured Ions3d0 : d-d transition is NOT possible2p 3s transition involves absorption of radiation in the UV region.

#The d-block metals and their compoundsimportant catalysts in industry and biological systemsCatalytic Properties of Transition Metals and their Compounds

#d-Block metalCatalystReaction catalyzedVV2O5 orvanadate(V) (VO3)Contact process2SO2(g) + O2 (g) 2SO3(g)FeFeHaber processN2(g) + 3H2(g) 2NH3(g)

The use of some d-block metals and their compounds as catalysts in industry

#d-Block metalCatalystReaction catalyzedNiNiHardening of vegetable oil(Manufacture of margarine)RCH = CH2 + H2 RCH2CH3PtPtCatalytic oxidation of ammonia(Manufacture of nitric(V) acid)4NH3(g) + 5O2(g) 4NO(g) + 6H2O(l)

The use of some d-block metals and their compounds as catalysts in industry

#The d-block metals and their compounds exert their catalytic actions in eitherheterogeneous catalysishomogeneous catalysisCatalytic Properties of Transition Metals and their Compounds

#Generally speaking, the function of a catalystprovides an alternative reaction pathway of lower activation energyenables the reaction to proceed faster than the uncatalyzed oneCatalytic Properties of Transition Metals and their Compounds

#1.Heterogeneous CatalysisThe catalyst and reactantsexist in different statesThe most common heterogeneous catalystsfinely divided solids for gaseous reactions

#1.Heterogeneous CatalysisA heterogeneous catalyst provides a suitable reaction surface for the reactants to come close together and react.

#1.Heterogeneous CatalysisExample:The synthesis of gaseous ammonia from nitrogen and hydrogen (i.e. Haberprocess)N2(g) + 3H2(g) 2NH3(g)

#1.Heterogeneous CatalysisIn the absence of a catalystthe formation of gaseous ammonia proceeds at an extremely low rateThe probability of collision of four gaseous molecules (i.e. one nitrogen and three hydrogen molecules)very small

#1.Heterogeneous CatalysisThe four reactant moleculescollide in proper orientation in order to form the productThe bond enthalpy of the reactant (N N), very largethe reaction has a high activation energy

#1.Heterogeneous CatalysisIn the presence of iron as catalystthe reaction proceeds much fasterprovides an alternative reaction pathway of lower activation energy

#1.Heterogeneous CatalysisFe is asolidH2, N2 and NH3 are gasesThe catalytic action occurs at the interface between these two statesThe metal provides an active reaction surface for the reaction to occur

#1.Heterogeneous Catalysis1.Gaseous nitrogen and hydrogen moleculesdiffuse to the surface of the catalyst2.The gaseous reactant moleculesadsorbed (i.e. adhered) on the surface of the catalyst

#1.Heterogeneous CatalysisThe iron metalmany 3d electrons and low-lying vacant 3d orbitalsform bonds with the reactant moleculesadsorb them on its surfaceweakens the bonds present in the reactant molecules

#1.Heterogeneous Catalysis2.The free nitrogen and hydrogen atoms come into contact with each otherreadily to react and form the product3.The weak interaction between the product and the iron surfacegaseous ammonia molecules desorb easily

#

The catalytic mechanism of the formation of gaseous ammonia from nitrogen and hydrogen

#


#


#


#


#43.3 Characteristic Properties of the d-Block Elements and their compound (SB p.162)1.Heterogeneous CatalysisSometimes, the reactantsin aqueous or liquid stateOther example:The decomposition of hydrogen peroxide2H2O2(aq) 2H2O(l) + O2(g)MnO2(s) as the catalyst

#

Energy profiles of the reaction of nitrogen and hydrogen to form gaseous ammonia in the presence and absence of a heterogeneous catalyst

#2.Homogeneous CatalysisA homogeneous catalystthe same state as the reactants and productsthe catalyst forms an intermediate with the reactants in the reactionchanges the reaction mechanism to an another one with a lower activation energy

#2.Homogeneous CatalysisIn homogeneous catalysis, the ability of the d-block metals to exhibit variableoxidation states enables the formation of the reaction intermediates.Example:The reaction between peroxodisulphate(VI) ions (S2O82) and iodide ions (I)

#2.Homogeneous CatalysisPeroxodisulphate(VI) ionsoxidize iodide ions to iodine in an aqueous solutionthemselves being reduced to sulphate(VI) ionsS2O82(aq) + 2I(aq) 2SO42(aq) + I2 (aq)

#2.Homogeneous CatalysisIron(III) ionstake part in the reaction by oxidizingiodide ions to iodinethemselves being reduced to iron(II) ions2I(aq) + 2Fe3+(aq) I2(aq) + 2Fe2+(aq) = +0.23 V

The reaction is very slow due to strong repulsion between like charges.

#2.Homogeneous CatalysisIron(II) ionssubsequently oxidized by peroxodisulphate(VI) ionthe original iron(III) ions are regenerated

2Fe2+(aq) + S2O82(aq)2Fe3+(aq) + 2SO42(aq) = +1.28 V

#2.Homogeneous CatalysisThe overall reaction:2I(aq) + 2Fe3+(aq) I2(aq) + 2Fe2+(aq) = +0.23 V

S2O82(aq) + 2I(aq)2SO42(aq) + I2(aq) = +1.51 V

2Fe2+(aq) + S2O82(aq)+)2Fe3+(aq) + 2SO42(aq) = +1.28 V

Feasible reaction

#43.3 Characteristic Properties of the d-Block Elements and their compound (SB p.164)2.Homogeneous CatalysisIron(III) ionscatalyze the reactionacting as an intermediate for the transfer of electrons between peroxodisulphate(VI) ions and iodide ions

#2.Homogeneous CatalysisIodide ionsreduce Fe3+ to Fe2+Peroxodisulphate(VI) ionsoxidize Fe2+ to Fe3+

#

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