THE d- AND f-BLOCK ELEMENTS

Introduction to d-block elements

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• In the periodic table the d block consist of the elements of group 3 to 12.

• The d orbital of the d-block elements in four periods are filled.

• The three series of the transitionmetals are 3d series from Sc to Zn, 4d series from Y to Cd and 5dseries from La

• to Hg.

• The fourth 6dseries begins from Ac and is incomplete till now.

Position of d-block in periodic table

• The d-block elements are found in the middle section of s- and p- block elements in the periodic elements.

• This lead to its name ‘transition’ due to its position between s- and p- block elements.

Electronic Configurations of the d-Block Elements

• The electronic configuration of d-block elements is(n-1) d^1–10ns^1–2. They have two incomplete outershells.

• Where (n–1) = Inner d orbitals having electrons from 1-10.

• ns = Outermost orbital may have one or two

• (n-1) d¹⁰n s²represents the electronic configurations of Zn, Cd and Hg.

• They exhibit variable valency that differ by units of one.

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Physical Properties

• The transition metals are hard and tough. They have low volatility butZn, Cd and Hg are an exception.

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• They have high melting and boilingpoints due to the greaterquantity of electrons from (n-1) d along with the ns electrons metallic

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Fig. The trends in melting point of d-block elements.

• Metals possessing high boiling point are noble in their

• The metals belonging to second and third series have greater enthalpies ofatomisation than the elements belonging to first series.

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Fig. Enthalpies of atomisation

Metallic characteristics:

• All transition metals exhibit metallic character.

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• They are good conductors of heat and electricity.

Fig. Metal is used at the tip of the plug that is inserted into the socket

• They are hard and tough.

• Being metal they exhibit the property of malleability, ductility and sonorousity.

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Fig. Aluminium is beaten into thin sheets to make aluminium foil used to pack food (Malleability)

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Fig. bells in temples are made of metal that when struck against hard surface produces sound (Sonorousity)

Fig. Metals are drawn into wires (Ductility)

• They form alloys by combining with some other metals.

• They are found to exist in face- centered cubic (fcc) structure, hexagonal close-packed (hcp) structure and body-centered cubic (bcc) structure.

• The transition elements exhibit covalent as well as metallic bonding within the atoms.

Atomic radii

• The atomic radii of the elements of 3d-series decreases as the atomic number increases.

• The atomic radii increase from 3d to 4d, the atomic radii of the 4d and 5d transition series are very close due to lanthanoid contraction. For example, Zirconium and Hafnium.

• This decrease in the metallic radius due to increase in the atomic mass leads to an increase in the density of elements. Consequently the density increases from titanium to copper.

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Ionisation Enthalpies

• Transition elements have small size which results in high ionization energy.

• They exhibit less electro positivity than the s-block elements due to their ionization potentials lying between S and P block elements.

• They form covalent compounds.

• The d-block elements exhibit an increase in the ionization potentials from left to right due to the screening effect of the new electrons added into the (n-1) d subshell.

• The first transition series exhibit an increase in the second ionisation energies with the increase in atomic number due to stable electronic configuration.

• Ionization energy decreases down the group.

• Ionization energy increases across the period.

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Oxidation States

• The number allotted to an element in a compound representing the number of electrons lost or gained by an atom of the element of the compound is called oxidation state.

For example, the electron configuration of copper is [Ar] 3d¹⁰ 4s¹. It attains noble gas configuration by losing one electron. The energy required to lose one more electron is very less and hence copper loses 2 electrons and forms Cu²⁺ ion. Therefore copper exhibits +1 and +2 oxidation state. But +2 oxidation states are more common.

It forms compounds like CuCl₂ and also with oxygen like CuO. In both the cases the oxidation state of Cu is +2.

• Transition elements exhibit varying oxidation states due to the minor energy difference between ns and (n -1) d orbitals.

• Along with ns electrons, (n -1) d electrons takes part in bonding. But due to the availability of few electrons for bonding Scandium does not show variable oxidation states.

• Due to presence of more d electrons, zinc has less orbital available for bonding and hence does not exhibit varying oxidation state.

• Among d-block elements the elements belonging to 8th group exhibit maximum oxidation state.

• Among the elements of 3d –series Manganese belonging to 7th group exhibits maximum oxidation state.

• Among the elements of 4d-Series Ruthenium belonging to 8th group exhibits maximum oxidation state.

• Among the elements of 5d-Series Osmium belonging to 8th group exhibits maximum oxidation state.

• The oxidation number of a free element is always 0.

• Oxidation number of (group I) elements like Li, Na, K, Rb, Cs is +1.

• Oxidation number of (group II) elements like Be, Mg, Ca, Sr, Ba is +2.

• Oxidation number of oxygen is -2.

• For example, oxidation state of Phosphorous in the compound HPO32- can be calculated by the following method:

Oxidation state of H = +1

Oxidation state of O = -2

Oxidation state of O₃ = 3(-2) [Since it has 3 atoms of oxygen.]

Overall oxidation state of the compound = -2

Let P represent the oxidation state of Phosphorous.

Therefore,

HPO₃^2-= +1+P+3(-2) = -2

• P = +3

Standard hydrogen electrode

• The electrode is connected to a standard hydrogen electrode (SHE) to constitute a cell

• It consists of a platinum electrodecoated with a layer of platinum black.

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• The electrode is immersed in an acidicsolution and the pure hydrogen gas is bubbled through it.

• Theconcentration of the reduced form and the oxidized form of hydrogen issustained at unity with following conditions:

• Pressure of hydrogen gas = 1 bar

• Concentration of hydrogen ion in the solution = 1 molar

E_cell = E_cathode – E_anode

E_cell = E_cathode – 0 = E_cathode

• The measured Emf of the cell:

Pt| H₂ (1 bar)| H⁺ (1M) || Cu²⁺(1M)| Cu is 0.34 V.

The positive value of the standard electrode potential signifies the easy reduction of Cu²⁺ ions than H⁺ ions.

• The measured Emf of the cell

Pt| H₂ (1 bar)| H⁺ (1M) || Zn²⁺(1M)| Zn is -0.76 V.

The negative value of the standard electrode potential signifies that the hydrogen ions oxidizes the zinc (or it can be said that zinc can reduce hydrogen ions).

• An electrode with standard electrode potential greater than zero is stable in its reduced form compared tohydrogen gas.

• Whereas an electrode with negative standard electrode potential is less stable in its reduced form compared to hydrogen gas.

• This decreases the standard electrodepotential which in turn decreases the oxidizing power ofthe specific electrode on the left and increases the reducing power of the electrodeto the right of the reaction.

Magnetic Properties

Substances, depending on their behaviour in an external magnetic field, are classified into 2 types:

Paramagnetic

• They are weakly attracted on application of magnetic field due to presence of one or more unpaired electrons that gets attracted by the magnetic field.

• Application of a magnetic field magnetizes the paramagnetic substances in the same direction but lose their magnetism in the absence of magnetic field.

• O₂, Cu²⁺, Fe³⁺, Cr³⁺ are some examples of such substances.

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Fig. A trickle of liquid oxygen is deflected by a magnetic field, illustrating its paramagnetism.

Diamagnetic

• They are weakly repelled by a magnetic field due to the absence of unpaired electrons.

• They are weakly magnetized on application of magnetic field in opposite direction.

• Pairing of electrons cancels out their magnetic moments and they lose their magnetic character.

• For example, H₂O, NaCl and C₆H₆ are some examples of such substances.

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In 3d series the orbital angular momentum of the electrons of the elements is less due to which they exhibit less contribution.

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The magnetic moment for these elements is calculated using the spin only formula

μ = √(n(n+2))

Where n = number of unpaired electrons

μ = magnetic moment in units of Bohr Magneton (BM).

PROBLEM: Calculate the ‘spin only’ magnetic moment of M2+(aq) ion (Z = 27).

SOLUTION: Z = 27 = [Ar] 3d⁷ 4s²

M²⁺ = [Ar] 3d⁷

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This means that it has 3 unpaired electrons.

n = 3

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Formation of Coloured Ions

• An electron from a lower energy d orbital is excited to a higherenergy d orbital, the energy of excitation corresponds to the frequencyof light absorbed.

• This frequency generally lies in the visible

• The colour of the transition metal ions is due to the presence of unpaired or incomplete d-orbitals.

• The absorption of visible light and hence coloured nature of the transition metal cations is due to the promotion of one or more unpaired d-electron from a lower to a higher level within the same d-subshell. This promotion requires small amount of energy available in the visible light.

• Sc³⁺, Ti⁴⁺, Cu⁺ and Zn²⁺ have either entirely empty or entirely filled 3d-orbital, i.e. they do not have any unpaired d-electron, and hence appear colourless.

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Formation of Complex Compounds

• The cations of transition metals have great tendency to form complexes with several molecules or ions called ligands.

• The bonds involved in the formation of complexes are coordinate and hence the complexes are called coordinate complexes.

• The structure of these complex ions is linear, square, planar, tetrahedral, octahedral depending upon nature of hybridization of metal ions.

• The weak ligand like CO, NO forms complexes only when transition metals are in zero due to the availability of vacant orbitals in the donor atom of the ligand in addition to lone pair.

• The highly electronegative and basic ligand like F-, Cl- can form complexes with transition metals even though there are in high oxidation states due to the presence of small, highly charged or neutral ligands with lone pair of electrons that can form strong sigma bond by donating a lone pair of electrons.

• In a transition series the stability of complexes increases with the rise in atomic number.

• The transition metal atom reveals multiple oxidation state; the higher valent ion forms more stable complexes.

• A few examples are:

• [Fe (CN)6]^3–

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• [Fe(CN)6]^4–

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• [Cu(NH3)4]²⁺

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• [PtCl4]^2–

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Formation of Interstitial Compounds

• Transition elements in combination with small atoms like H, B, C, N etc. leads to the formation of interstitial compounds that are non-stoichiometric in composition.

E.g.: TiH_1.3, VH_0.54

• The interstitial compounds so formed are chemically inert having higher melting points as compared to pure metals. These componds are hard and tough and keeps metallic conductivity.

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Alloy Formation

• Alloys are homogeneous mixtures of more than one metal that can displace another metal from the crystal lattice due to their comparable sizes. This leads to the formation of alloys.

• The alloys so formed are hard with high melting points. For example, chromium, vanadium, tungsten, manganese, molybdenum are the ferrous alloys.

• Some other examples are brass (alloy of copper + zinc), stainless steel, bronze (alloy of copper + tin), etc.

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Non-stoichiometric Compounds

• The compounds in which the there is no conformity in chemical composition with the ideal chemical formula are called non-stoichiometric compounds.

• These compounds are formed due to variable valency in transition metals and also due to the defects arising in solid state.

• The compounds formed with O, S, Se, Te, Fe, Zn etc. are the examples of such compounds.

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Preparation of K₂Cr₂O₇

Potassium dichromate, (K₂Cr₂O₇) is an orange-ish inorganic chemical reagent. In different laboratory or industry it is basically used as an oxidizing agent usually for alcohols.

It can be prepared through the following process:

• At first the fusion of chromite ore FeCr₂O₄ with sodium or potassium carbonate in the presence of access of air.

4FeCr₂O₄ + 8Na₂CO₃ + 7O₂ –> 8Na₂CrO₄ + 2FeO₃ + 8CO₂

• Solution of sodium chromate is first filtered and then acidified with a solution of sulfuric acid which results in an orange sodium dichromate solution Na₂Cr₂O₇ 2H₂O can be crystallized.

2Na₂CrO₄ + 2H⁺ –> Na₂Cr₂O₇ + 2Na⁺ + H₂O

• Sodium dichromate is more soluble than potassium dichromate and therefore it is fused with KCl that leads to the formation of orange crystals of potassium dichromate.

Na₂Cr₂O₇ + 2KCl –> K₂Cr₂O₇ + 2NaCl

• At pH equal to 4 the dichromates and chromates exists in equilibrium and can be inter convertible.

2CrO₄ ^2- + 2H²⁺ –> Cr₂O₇^2- + H₂O

Cr₂O₇ ^2- + 2OH- –> 2CrO₄^2- + H₂O

• The yellow colour of chromate changes to orange coloured dichromate in the presence of acidic medium whereas the dichromate changes into chromate in the presence of basic medium.

2CrO₄^2- + 2H⁺ –> 2HCrO₄^– (Hydrogen chromate)
2HCrO⁴^– —> Cr₂O₇^2- + H₂O Dichromate (orange)

• The chromate ion is tetrahedral and the dichromate ion consists of two tetrahedral sharing at one corner, with Cr-O-Cr bond angle 126 degree.

Properties of Potassium dichromate (K₂Cr₂O₇)

Oxidizing properties

Potassium dichromate is a powerful oxidizing-agent in an acidic medium.

Cr₂O₇ ^2- + 14H⁺ + 6 electron –> 2Cr³⁺ + 7H₂O

It oxidizes iodides to iodine.

Cr₂O7 ^2- + 14H⁺ + 6I^– –> 2Cr ³⁺ + 7H₂O + 3I₂

It oxidizes ferrous salts to ferric salts.

Cr₂O₇ ^2- + 14H⁺ + 6 Fe2+ –> 2Cr ³⁺+ 7H₂O + 6Fe³⁺

It oxidizes stannous salts to stannic salts.

Cr₂O₇ ^2- + 14H⁺ + 3Sn ²⁺ –> 2Cr ³⁺ + 7H₂O + 3Sn ⁴⁺

It oxidizes H2S to sulphur.

Cr₂O₇ ^2- + 8H⁺ + 3H₂S –> 2Cr ³⁺ + 7H₂O + 3S

Action of heat

Application of heat leads to the decomposition of Potassium dichromate leading to the formation of potassium chromate, chromic oxide and oxygen.

4K₂Cr₂O₇ -Heat-> 4K₂CrO₄ + 2CrO₃ + 3O₂

Preparation of Pottassium Permanganate (KMnO₄)

Pottassium Permanganate (KMnO₄) is a dark purple solid consisting of two ions: a potassium ion (K⁺) and a permanganate ion (MnO^{− 4}). It is a strong oxidizing agent and also possess medication properties due to which it is extensively used to clean wounds and in dermatitis.

• Fusion of powdered Pyrolusite ore (MnO₂) with an alkali metal hydroxide like KOH in the presence of air or an oxidizing agent like KNO₃ leads to the formation of dark green potassium Manganate (K₂MnO₄) which disproportionate either in a neutral or acidic medium and results in the formation of potassium permanganate.

2 MnO₂ + 4 KOH + O₂ –> 2K₂MnO₄ + 2H₂O
3 MnO₄^2- + 4H⁺ —> 2MnO₄^– + MnO₂ + 2H₂O

• Potassium permanganate is commercially prepared by an alkaline oxidative fusion of Pyrolusite ore (MnO₂) and again by the electrolytic oxidation of manganate (4) ion.

2 MnO₂+ 4KOH + O₂ –> 2K₂MnO₄ + 2H₂O
MnO₄^2- + (electrolytic oxidation) —> MnO₄^– + e^–

Introductiontof-BlockElements

• These elements are also called inner transition elements because the last electron enters (n−2) f-orbital, i.e.inner tothepenultimateenergylevelandformsatransitionseries.

• Thegeneralelectronicconfigurationoftheseelementscanbegivenas

Hence, theyhavethreeincompleteshells, viz. (n−2), (n−1)andnth.

Classificationoff-blockelements

Lanthanoids:

· TheyarecalledLanthanoids becausetheycomeimmediatelyafterLanthanum.

· Theyarealsocalled4f-blockelementsorfirst innertransitionserieselementsorlanthanidesor lanthanons.

Actinoids:

· TheyarecalledActinoids becausetheycomeimmediatelyafter Actinium.

· Theyarealsocalled5f-blockelementsorsecondinnertransitionserieselementsoractinidesor actinons.

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TheLanthanoids:

ElectronicConfiguration:

• Lanthanoidshavethecommon electronicconfigurationof6s2andelectronsoccupying4flevelvariably. The electronic configuration of all the tripositive ions are of the form 4fn (n = 1 −14)withincreasingatomicnumber.

• The electronic configuration of Europium (Z = 63) is 4f7 6s2 and that of Gadolinium (Z = 64) is4f7 5d1 6s2. This can be explained on the basis of extra stability of the half-filled orbitals in theircores.

• TheelectronicconfigurationofYtterbium(Z=70)is4f146s2andthatofLutetium (Z=71)is4f14 5d1 6s2. This is also explained on the basis of extra stability of the filled orbitals in theircores.

Oxidationstates:

• Thecommonoxidationstateofthelanthanoidsis+3.

• The+2and+4oxidationstates areverylesscommon.Theseareexhibitedbythoseelementswhichattainastableelectronic configurationoff0,f7orf14bylosing2or 4electrons.

• Here,eachelement triestoattainthestableoxidationstatebylosingor gainingelectrons,i.e.

+3.Hence,Sm2+,Eu2+andYb2+ionsinsolutionsaregoodreducing agentsandaqueoussolutionsofCe4+ andTb4+aregoodoxidisingagents.

AtomicandionicradiiofLanthanoids:

• In lanthanoids, if the atomic number increases, atomic and ionic radii decrease from La3+ toLu3+.

Variationofionicradiioftrivalentlanthanoids

• Causesoflanthanoidcontraction:

1.Whenwemovefrom lefttorightalongthelanthanoidseries,thenuclearchargeincreasesby one unit at each neighbouring element. The new electron is added to the samesubshell. So, the attractive force between the electron and nucleus increases, and hence,thesizedecreases.

2.When a new electron is added to the f-subshell, the shielding effect of one electron byanotherisnot perfectduetotheshapeof f-orbitals. Suchashieldingcannot balancetheeffect ofincreasednuclear charge.Hence, contractionoccurs.

• Consequencesoflanthanoidcontraction:

(a)Difficultyinseparationoflanthanoids:

1.Becauseoftheslightdifferenceinionicradiioflanthanoids,theirchemicalpropertiesaresimilar.Thismakesseparationoflanthanoidsmoredifficult.

2.Also,duetothedifferenceinthesizeoflanthanoids, propertiessuchas solubility,complex ion formation and hydration show differences. This helps separate theindividuallanthanoids by the ionexchangemethod.

(b)Similarity in the size of elements belonging to the same group of the second and thirdtransitionseries:

1.The size of elements belonging to the second transition series is always greater thanthatoftheelementsbelongingtothesamegroupofthefirsttransitionseries.Also, thesize of the atom of the third transition series, i.e. after lanthanum, is nearly the sameas that of the atom of the element belonging to the same group of the secondtransitionseries.

2.Similarity in size of the atoms of the elements belonging to the same group of the 2^ndand3^rd transitionseriesisduetotheeffect oflanthanoidcontraction.

(c)Effectonthebasicstrengthofhydroxides:

BecausethesizeoflanthanoidionsdecreasesfromLa3+toLu3+,thecovalentcharacterof the hydroxides increases, and hence, the basic strength decreases. Therefore,La(OH)3ismorebasic,whileLu(OH)3isweaklybasic.

CharacteristicsofLanthanoids:

(a)Silveryappearanceandsoftness:

All lanthanoids are silvery white soft metals and tarnish easily in air. As the atomic numberincreases, their hardness alsoincreases.

(b)Meltingpoint:

They have a very high-melting point in the range 1000−1200 K except samarium, which has ahighmeltingpointofabout1623K.

(c)Electricalandthermalconductivity:

Theyhavemetalliccharacteristics,andhence, theyaregoodconductorsofheat andelectricity.

(d)Density:

They have high densities in the range of 6.77−9.74 gcm⁻³. Density and other properties differsmoothlywithincreasingatomicnumberexceptinEuandYb.

(e)Colour:

Theyaresilverywhite.Most ofthetrivalentionsarecolouredinsolidandinaqueoussolution.Thisis duetof–ftransition.

(f)Magneticbehaviour:

Allthelanthanoidsexcept La³⁺ andLu³⁺ showparamagnetism.Thispropertyisduetothepresenceofunpairedelectronsintheincomplete4fsubshell.

(g)Ionisationenthalpies:

The first ionisation enthalpies of lanthanoids are about 600 kJ mol⁻¹ and the second is about1200kJmol⁻¹.Thethirdionisationenthalpyislowifitleadstoastableelectronicconfiguration,

i.e.empty,half-filledorcompletelyfilled.

(h)Electropositivecharacter:

Theyarehighlyelectropositivebecausetheypossesslowionisationenthalpy.

(i)Standardelectrodepotential:

Thevalueoftheirstandardelectrodepotential,i.e.Eoforhalf-reaction,M³⁺ (aq) + 3e^– M(s),liesintherange−2.2to −2.4V. Europiumis anexceptionbecauseitsEovalueis−2.0V.

(j)Reducingagents:

Theyeasilyloseelectrons;hence, theyaregoodreducingagents.

(k)Complexformation:

Because of their large size and low charge density, they do not have much tendency to formcomplexes.Thistendencyofcomplexformationincreaseswithincreasingatomicnumber.

(l)Chemicalbehaviour:

The first few elements of the series are more reactive like calcium. As the atomic numberincreases, their behaviour becomes similar to that of aluminium. They show the followingproperties:

.....

Theycombinewithhydrogenonheating.

Theyformcarbideswhenheatedwithcarbon.

Theyformhalideswhenburntwithhalogens.

Theyreactwithdilute acidstoliberatehydrogengas.

Theyformoxidesandhydroxides.

Usesoflanthanoids:

1.Itismainlyusedintheproductionofalloysteelstoimprovethestrengthofsteel.Awell-knownalloyismischmetalwhichhasthe followingcomposition:

Lanthanoidmetal=95%

(about50%Ce,40%La andtherestotherlanthanoids)

Iron= 5%

S, C,CaandAl=traces

The mischmetal is mostly used in making a magnesium-based alloy. It is pyrophoric alloy, i.e.analloywhichemitssparkswhenstruck. Itisusedinmakingbullets, shellsandlighterflints.

2.Theiroxidesareusedintheglassindustry—forpolishingglassandtomakeopticalglass.

3.Mixedoxidesof lanthanoidsare usedascatalystsinpetroleumcracking.

4.Cericsulphateisa well-knownoxidisingagentusedinvolumetricanalysis.

Actinoids

ElectronicConfiguration:

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• Alltheactinoidshavecommon7s2configuration,andfillingofthe5fand6dsubshellsisvariable.

• The14electronsarebeingaddedto5f,exceptinthorium(Z=90),butthisfillingofthe5fsubshellcontinuesfurther afterthoriumtill5forbitalsarecompleteatZ= 103.

• Irregularitiesintheelectronicconfigurationsofactinoidsareconcernedwiththestabilitiesoff0,f7andf14configurations.

• Althoughthe4fand5forbitalshavesimilarshapes,5fislessdeeplyburiedthan4f.Hence,5felectronscanparticipateinbonding.

Oxidationstate:

• Thecommonoxidationstateofallactinoidsis+3.

• Actinoids also possessthe oxidation state of+4. Some of themshow higher oxidation state.The oxidation state gradually increases from the extreme left to the middle of the series andthendecreases.

• Thecompoundsofactinoidswith+3and+4oxidationstatesundergohydrolysis.

Ionicradiiandactinoidcontraction:

• Likelanthanoids,actinoidsalsoshowcontractionduetothepoorshieldingeffectofthe5f-electrons.

• So,theradiiof theatomsorionsof actinoidsdecreasegraduallyalongtheseries.

• Thiscontraction isgreaterfromelementto elementin a seriesbecause5forbitalsextend inthespacebeyond6s and6porbitals.

CharacteristicsofActinoids:

(a)Silveryappearance:

Actinoidsaremetalswithsilveryappearance.

(b)Structuralvariability:

Theyhavemuchmoreregularitiesintheirmetallicradii;hence,theyshowgreatstructuralvariability.

(c)Colour:

Theyaresilverywhitemetals.Theircationsaregenerallycoloured.Thecolourofthesecationsdependsonthenumberof5f-electrons.

Thecationscontainingzero5felectronsorseven5felectronsarecolourless.Thecationscontaining2−65felectronsarecoloured.

Thiscolourmainlyarisesbecauseof f–f transition.

(d)Meltingandboilingpoints:

Actinoidshavehigh meltingandboilingpoints. Theydonot showanygradualchangeevenwithincreasingatomicnumber.

(e)Density:

Withtheexceptionofthoriumandamericium,allactinoidshavehighdensities.

(f)Ionisationenthalpies:

They have low ionisation enthalpies than lanthanoids. This is because 5f is less penetratingthan4fandhenceismoreeffectivein shieldingfromnuclear charge.

(g)Electropositivecharacter:

Theyarehighlyelectropositive.

(h)Magneticbehaviour:

Theyarestronglyparamagnetic.Thechangeinmagneticsusceptibilityofactinoidswithincreasing number of unpaired electrons is the same as lanthanoids, but the values are higherforactinoids.

(i)Reducingagents:

Alltheactinoidsarestrongreducingagents.

(j)Radioactivity:

All the actinoids are radioactive. The first few members of the series have long half-lives. Theremaininghave halflivesrangingfromveryfewdays tofewminutes.

(k)Chemicalbehaviour:

Theyarehighlyreactiveinthecrushedform.Theyshow thefollowingproperties:

Usesof actinoids:

...

•It is used in atomicreactors and intreatmentofcancer.

•Its salts are used inmaking incandescentgasmantles.

Usesofthorium

...

•Itisusedasnuclearfuel.

•Its salts are used inglass, textile, ceramicindustries and inmedicines.

Usesofuranium

...

•Itisusedasafuelforatomicreactors.

•It is also used formakingbombs.

Usesofplutonium

ComparisonofLanthanoidsandActinoids

Similarities:

Actinoidsshow

Both showcommonoxidationstateof+3.

Both areelectropositiveand veryreactive.

Both exhibitmagnetic andspectralproperties.

actinoid

con and

traction

l ds

anthanoi

show

la id

nthano

contraction.

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Comparison of Actinoids with Lanthanoids

General Characteristics and Comparison of Actinoids with Lanthanoids

(i) Electronic configuration

The general electronic configuration for actinoids is [Rn]⁸⁶ 5f^1-14 6d0^-1 7s² and for lanthanoids is [Xe]⁵⁴ 4f^0-14 5d^0-1 6s².

(ii) Atomic and lonic sizes

Like lanthanoids the ionic radii of actinoids gradually decrease across the series due to the poor screening effect of nuclear charge exerted by the f electrons.

(iii) Oxidation states

The lanthanoids exhibit +3 oxidation states. Some elements may exhibit +2 and +4 oxidation states due to extra stability of fully-filled and half-filled orbitals.

On the other hand Actinoids also exhibit +3 oxidation state. They also exhibit varying oxidation states due to the comparable energies of 5f, 6d, and 7s.

(iv) Chemical reactivity

◦ Earlier members of the lanthanide series are more reactive and are comparable to CSolution: They resemble Al with increasing atomic number.

◦ Finely divided Actinoids are highly reactive metals and when added to boiling water gives a mixture of oxide and hydride.

◦ At moderate temperatures Actinoids combine with most of the non-metallic elements.

◦ Actinoids remain unaffected by the action of alkalies but gets slightly affected by nitric acid due to the formation of a protective oxide layer.

Applications of d- and f-Block elements

Iron and steels are used for making tools, utensils, vehicles, bridges and much more.

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TiO for the pigment industry and MnO₂ for use in dry battery cells.

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Zn and Ni/Cd is also used for battery industry.

Elements of Group 11 called the coinage metals.

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V₂O₅ catalyses the oxidation of SO₂ in the manufacture ofsulphuric acid.

TiCl₄ with A1(CH₃)₃ forms the basis of the Ziegler catalystsused to manufacture polyethylene (polythene).

Iron catalysts are used inthe Haber process for the production of ammonia from N₂/H₂mixtures.

Nickel catalysts enable the hydrogenation of fats

Wackerprocess the oxidation of ethyne to ethanal is catalysed by PdCl₂.

Nickel useful in the polymerisation of alkynes and other organiccompounds such as benzene.

The photographic industry relies on thespecial light-sensitive properties of AgBr.

Problem: Write down the electronic configuration of:

(i) Cr³⁺ (iii)Cu⁺ (v)Co²⁺ (vii)Mn²⁺

(ii) Pm³⁺ (iv)Ce⁴⁺ (vi) Lu²⁺ (viii)Th⁴⁺

Solution:

(i) Cr³⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d³

Or, [Ar]¹⁸3d³

(ii) Pm³⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰5s² 5p⁶ 4f⁴

Or, [Xe]⁵⁴ 3d³

(iii) Cu⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰

Or, [Ar]¹⁸ 3d¹⁰

(iv) Ce⁴⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶

Or, [Xe]⁵⁴

(v) Co²⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁷

Or, [Ar]¹⁸3d⁷

(vi) Lu²⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 4f¹⁴ 5d¹

Or, [Xe]⁵⁴2f¹⁴3d³

(vii) Mn²⁺: 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁵

Or, [Ar]¹⁸ 3d⁵

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