D and F Block Elements Class 12 Chemistry PDF

CLASS 12, CHEMISTRY, CHAPTER NO. 8 THE d and f- BLOCK ELEMENTS MEGHA SOLANKI, PGT- CHEMISTRY, KV MANKHURD, MU  REVISED SYLLABUS FOR 2020-21 General introduction. electronic configuration. occurrence and characteristics of transition metals. General trends in proper...

CLASS 12, CHEMISTRY, CHAPTER NO. 8 THE d and f- BLOCK ELEMENTS MEGHA SOLANKI, PGT- CHEMISTRY, KV MANKHURD, MU  REVISED SYLLABUS FOR 2020-21 General introduction. electronic configuration. occurrence and characteristics of transition metals. General trends in properties of the first row transition metals – - metallic character. - ionization enthalpy. - oxidation states. - ionic radii. - colour. - catalytic property. - magnetic properties. - interstitial compounds. - alloy formation. Lanthanoids - Electronic configuration - oxidation states. - lanthanoid contraction and its consequences. Ionisation Enthalpies  TRENDS IN STABILITY OF HIGHER OXIDATION STATES IN HALIDES The highest oxidation numbers are achieved in TiX4 (tetrahalides), VF5 and CrF6. +7 state for Mn is not represented in simple halides but MnO3F (Manganese oxyfluoride)is known.(MnF7 will have too much steric effect and too much repulsion among F atoms hence it does not exist but O forms multiple bonds and that’s why no. of species becomes lesser in the molecule and is stabilised.)  All the highest OS are found with fluorine because it stabilize the highest OS by forming very strong bond due to being most electronegative. (high bond enthalpy in covalent halides like VF5 and CrF6 and high lattice energy in ionic halides like CoF3.) Fluorides are unstable with lower OS and due to being most electronegative they oxidise the transition metal to its higher OS Vanadium halides are generally hydrolysed to give oxohalide VOX3. Sc forms trihalides with all the four halogens, F, Cl, Br and I. Cu forms dihalide with F and Cl(higher OS with more electronegative atoms) and mono halide with Cl, Br and I (less electronegative). Thus Cu2+ oxidises I– to I2: 2Cu 2+ + 4I − → Cu2I2 (s) + I2 However, many copper (I) compounds are unstable in aqueous solution and undergo disproportionation: 2Cu+ → Cu2+ + Cu The stability of Cu2+ (aq) rather than Cu+(aq) is due to the much more negative hydration enthalpy of Cu2+(aq) than Cu+, which compensates for the 2nd IE of Cu.  TRENDS IN STABILITY OF HIGHER OXIDATION STATES IN OXIDES The highest oxidation number in the oxides coincides with the group number and is attained in Sc2O3 to Mn2O7. Beyond Group 7, no higher oxides of Fe above Fe2O3, are known, although ferrates (VI)(FeO4)2–, are formed in alkaline media but they readily decompose to Fe2O3 and O2.  The ability of O to stabilise these high OS exceeds that of F due to The ability of oxygen to form multiple bonds to metals which decreases steric hinderance (less O atoms are needed than F for same OS) and form stronger bonds(multiple bonds are stronger than single bonds.) Thus the highest Mn fluoride is MnF4(OS +4)whereas the highest oxide is Mn2O7(OS +7). In the covalent oxide Mn2O7, each Mn is tetrahedrally surrounded by O’s including a Mn–O–Mn bridge. The tetrahedral [MO4]n- ions are known for VV, CrVl, MnV, MnVl and MnVII. ( Examples: [MnO4]–, [CrO4]2–, and [VO4]3–  Besides the oxides, oxocations stabilise Vv as VO2+, VIV as VO2+ and TiIV as TiO2+ (These are derived from oxohalides). There are three mixed oxides: Fe3O4 = FeO.Fe2O3 Mn3O4 = MnO.Mn2O3 Co3O4 = CoO.Co2O3 As usual oxides of highest OS (like Mn2O7, Cr2O6)are acidic in nature( tendency to gain electrons due to greater +ve charge on metal ion), lowest OS are basic and middle ones are amphoteric. V2O5 , in spite of having highest OS of V, have amphoteric properties (Although it is little more acidic than basic) In a transition series the acidic nature of oxides for the same OS increases from left to right due to decreasing size of metal which increases +ve charge density on it. As usual oxides of highest OS are covalent in nature due to more polarising power  Let’s apply your knowledge Q. How would you account for the increasing oxidising power in the series: VO2+< Cr2O72−< MnO4- ? Ans: This is due to the increasing stability of the species with lower oxidation state of metal atom to which they are reduced , e.g., Q. FeCl3 and FeCl2 are found as dimer in vapour phase. Explain the bonding in them. Ans: FeCl3​and FeCl2​exist in dimer form in vapour phase. In dimer form, they have (3C−4e−) bond. They contain chlorine bridges. Q. What happens if we dissolve anhydrous Mn2O7 in water? Ans: It is acidic in nature hence it produces permanganic acid Mn2O7 + H2O. -------> H2Mn2O8. ------>. 2HMnO4 Q. Write the anhydride of permanganic acid. Ans: HMnO4​is dehydrated by cold sulfuric acid to form its anhydride, Mn2O7 which is highly explosive in nature.  CHEMICAL REACTIVITY AND STANDARD ELECTRODE POTENTIAL The Chemical reactivity of transition metals can directly be explained by their standard electrode potential (E)values. Higher the negative E, the metal will be more reactive.(M tends to be M 2+ by forming compounds. Thus such metals are good reducing agents). Higher the positive E, the metal will be less reactive.(M 2+ tends to be M means its ions are easily displaced from its compounds to form elemental M. Thus such metals are good oxidizing agents.) In 3d series from left to right E for M2+/ M becomes less negative so reactivity also decreases. All of these except Cu can be oxidized by 1M H + ion solution(acids). Cu having positive E becomes least reactive in 3d series. Evalues for Mn, Ni and Zn are more negative than expected from the general trend. It is due to stabilities of half-filled d subshell (d5) in Mn2+, completely filled d subshell (d10) in Zn2+ and highest negative enthalpy of hydration for Ni 2+. Thus  The E values for the redox couple M3+/M2+ for Mn and Co are highly positive. It means M2+ ions are more stable than M3+ ions in case of these two metals. It is due to stability of half-filled d subshell (d5) in Mn2+ and stable complex formation of Co2+ with water. Hence Mn3+ and Co3+ ions are the strongest oxidising agents in aqueous solutions. The E values for the redox couple M3+/M2+ for Ti, V and Cr are negative. It means M3+ ions are more stable than M2+ ions in case of these three metals. It is due to t2g half filled d orbitals in Cr3+ and more hydration enthalpy as compared to ionisation enthalpy in Ti3+ and V3+. Hence their M2+ ions are strong reducing agents and will liberate hydrogen from a dilute acid and convert themselves in M3+ ions. 2Cr2+(aq) + 2H+(aq) → 2Cr3+(aq) + H2(g)  MAGNETIC PROPERTIES OF d-BLOCK ELEMENTS Many of the transition metal ions are paramagnetic. Para magnetism arises from the presence of unpaired electrons, each such electron having a magnetic moment associated with its spin angular momentum and orbital angular momentum. For the compounds of the first series of transition metals, the contribution of the orbital angular momentum is effectively quenched and hence is of no significance. (In order for an electron to contribute to the orbital angular momentum the orbital in which it resides must be able to transform into an exactly identical and degenerate orbital by a simple rotation without any energy consumption. In transition elements all the 5 d- orbitals are not same in shape and energy but they are in the form of t2g and eg energy levels. Hence Orbital angular moment is ignored.)  For these, the magnetic moment is determined by the number of unpaired electrons and is calculated by using the ‘spin-only’ formula, i.e., where n is the number of unpaired electrons and µ is the magnetic moment in units of Bohr magneton (BM). A single unpaired electron has a magnetic moment of 1.73 Bohr magnetons (BM). The magnetic moment increases with the increasing number of unpaired electrons. Thus, the observed magnetic moment gives a useful indication about the number of unpaired electrons present in the atom, molecule or ion.  Here, the observed values are somewhat different from calculated values. It depends on the compound of which the metal ion is a part. The other part (ligand) may affect the no. of unpaired electrons. They can cause pairing or unpairing of d- electrons of transition metals.  NOW SOLVE THIS: Q. Calculate the magnetic moment of a divalent ion in aqueous solution if its atomic number is 25. Solution: With atomic number 25, the divalent ion in aqueous solution will have d5 configuration (five unpaired electrons). The magnetic moment, µ is Q. Calculate the ‘spin only’ magnetic moment of M2+(aq) ion (Z = 27). Solution:  FORMATION OF COLOURED IONS When an electron from a lower energy d orbital is excited to a higher energy d orbital, the energy of excitation corresponds to the frequency of light absorbed. This frequency generally lies in the visible region. The colour observed corresponds to the complementary colour of the light absorbed. The frequency of the light absorbed is determined by the nature of the ligand.  In aqueous solutions where water molecules are the ligands, the colours of the ions observed are listed below: Colours of some of the first row transition metal compounds  FORMATION OF COMPLEX COPMOUNDS Complex compounds are those in which the metal ions bind a number of anions or neutral molecules giving complex species with characteristic properties. A few examples are: [Fe(CN)6]3–, [Fe(CN)6]4–, [Cu(NH3)4]2+ and [PtCl4]2–. (The chemistry of complex compounds is dealt with in detail in Unit 9). The transition metals form a large number of complex compounds. This is due to the comparatively smaller sizes of the metal ions, their high ionic charges and the availability of d orbitals for bond formation.  CATALYTIC PROPERTIES OF TRANSITION ELEMENTS The transition metals and their compounds are known for their catalytic Properties activity. This activity is due to their ability to adopt multiple oxidation states and to form complexes. Vanadium(V) oxide (in Contact Process), finely divided iron (in Haber’s Process), and nickel (in Catalytic Hydrogenation) are some of the examples. Catalysts at a solid surface involve the formation of bonds between reactant molecules and atoms of the surface of the catalyst (first row transition metals utilise 3d and 4s electrons for bonding). This has the effect of increasing the concentration of the reactants at the catalyst surface and also weakening of the bonds in the reacting molecules (the activation energy is lowering).  Also because the transition metal ions can change their oxidation states, they become more effective as catalysts. For example, iron(III) catalyses the reaction between iodide and persulphate ions. An explanation of this catalytic action can be given as:  Formation of Interstitial Compound Interstitial compounds are those which are formed when small atoms like H, C or N are trapped inside the crystal lattices of metals. They are usually non stoichiometric and are neither typically ionic nor covalent, for example, TiC, Mn4N, Fe3H, VH0.56 and TiH1.7, etc. The formulas quoted do not, of course, correspond to any normal oxidation state of the metal. Because of the nature of their composition, these compounds are referred to as interstitial compounds. The principal physical and chemical characteristics of these compounds are as follows: (i) They have high melting points, higher than those of pure metals. (ii) They are very hard, some borides(like TiB2)approach diamond in hardness. (iii) They retain metallic conductivity. Interstitial Compound of Fe and C (iv) They are chemically inert.  Alloy formation An alloy is a blend of metals prepared by mixing them Alloys may be homogeneous solid solutions in which the atoms of one metal are distributed randomly among the atoms of the other. Such alloys are formed by atoms with metallic radii that are within about 15 percent of each other. Because of similar radii and other characteristics of transition metals, alloys are readily formed by these metals. The alloys so formed are hard and have often high Mpt. The best known are ferrous alloys: chromium, vanadium, tungsten, molybdenum and manganese are used for the production of a variety of steels and stainless steel. Alloys of transition metals with non transition metals such as brass (copper-zinc) and bronze (copper-tin), are also of considerable industrial importance. Composition of some alloys  Oxides and Oxoanions of Metals These oxides are generally formed by the reaction of metals with oxygen at high temp. All the metals except scandium form MO oxides, which are ionic. The highest ON in the oxides coincides with the gr. No. and is seen in Sc 2O3 to Mn2O7. Beyond group 7, no higher oxides of iron above Fe2O3 are known. Besides the oxides, the oxo cations stabilise VV as VO2+, VIV as VO2+ and TiIV as TiO2+. As the ON of a metal increases, ionic character decreases. In the case of Mn, Mn 2O7 is a covalent green oil. Even CrO3 and V2O5 have low Mpt. In these higher oxides, the acidic character is predominant. Thus, Mn2O7 gives HMnO4 and CrO3 gives H2CrO4 and H2Cr2O7. V2O5 is amphoteric though mainly acidic and it gives VO43– as well as VO2+ salts. In V, there is gradual change from the basic V2O3 to less basic V2O4 and to amphoteric V2O5. V2O4 dissolves in acids to give VO2+ salts. Similarly, V2O5 reacts with alkalies as well as acids to give VO43− and VO4+ respectively.  f- BLOCK ELEMENTS The f-block consists of the two series: (1) Lanthanoids or 4f series(the fourteen elements following lanthanum) (2) Actinoids or 5f series(the fourteen elements following actinium). In 4f and 5f series elements, the last e- enters into 4f and 5f orbitals respectively hence they are called so. Both series together are called inner transition elements because they form transition series within the transition elements of d-block. if we keep lanthanides and actinides series in the main periodic table then the table will be too wide. That’s why These two series are kept in the bottom of the table. Wide form of the periodic table  The lanthanides resemble one another more closely than do the members of ordinary transition elements in any series. It is because they have only one stable oxidation state(M+3) and there are small changes in size and nuclear charge along a series as compared to other transition series. The chemistry of the actinides is, on the other hand, much more complicated. The complication arises partly owing to the occurrence of a wide range of oxidation states in these elements and partly because their radioactivity creates special problems in their study. La and Ac are considered d-block elements on the basis of their position in the periodic table but actually they belong to Lanthanoid and Actinoid family respectively on the basis of their chemical and physical properties. Thus we can say that 4f series contain 14 elements from Ce to Lu but Lanthanide family( denoted as Ln) consists of 15 elements from La to Lu. Same is true for 5f series also. The general ele. config. of these elements can be written as [Xe] 4f1-14 ,5d0-1, 6s2.  LANTHANOIDS GENERAL CHARACTERISTICS: They are called rare earth metals since the occurrence of these elements is very small (3×10-4 % of Earth’s crust). All the lanthanoids are silvery white soft metals and tarnish rapidly in air. The hardness increases with increasing atomic number, samarium being steel hard. Their melting points range between 1000 to 1200 K but samarium melts at 1623 K. They have typical metallic structure and are good conductors of heat and electricity. Density and other properties change smoothly except for Eu and Yb and occasionally for Sm and Tm. Lanthanoinds ATOMIC AND IONIC RADII: THE LANTHANIDES CONTRACTION The more than expected regular decrease in the atomic and ionic radii of lanthanide series from La to Lu due to least shielding effect of 4f electrons is called lanthanide contraction. This decrease is even more regular for trivalent ions(M3+).  CONSEQUENCES OF LANTHANIDES CONTRACTION (A) EFFECTS ON d- BLOCK ELEMENTS: 1. Silmilar atomic sizes of 3d and 4d transition series: As we go down from 3d to 4d in a group, the size should increase due to increasing no. of shells. But due to lanthanoid contraction, the effective nuclear charge is much more in 4d series as compared to the effect of increasing shell. Therefore, size of the atom of third transition series is nearly the same as that of the atom of the second transition series. For example: radius of Zr = radius of Hf radius of Nb = radius of Ta 2. Difficulty in the separation of 3d and 4d elements: As there is negligible change in the ionic radii of 3d and 4d series, these elements occur together in the nature and their chemical properties are similar. This makes the separation of elements in the pure state difficult. 3. High Ionization energy of 5d series: Attraction of electrons by the nuclear charge is much higher and hence Ionization energy of 5d elements are much larger than 4d and 3d. In 5d series, all elements except Pt and Au have filled s-shell. Iridium and Gold have the maximum Ionization Energy. (B) EFFECTS OF LANTHANIDE CONTRACTION ON LANTHENIDES: 1. DIFFICULTY IN SEPARATION OF LANTHANIDE ELEMENTS: However, there is a regular unexpected decrease in the size from La to Lu but the difference in the sizes of two consecutive lanthanide elements is still very small, which makes them difficult to separate from each other. 2. EFFECT ON THE BASIC STRENGTH OF HYDROXIDES: As the size of lanthanides decreases from La to Lu, the covalent character of the hydroxides increases and hence their basic strength decreases. Thus, La(OH)3 is more basic and Lu(OH)3 is the least basic. 3. COMPLEX FORMATION: Because of the smaller size but higher nuclear charge, tendency to form coordinate. Complexes increases from La3+ to Lu3+. 4. INCREASE IN ELECTRONEGATIVITY FROM LA TO LU: Due to decrease in size, the hold of nucleus on3.outer most electrons increase and hence ionisation enthalpy and electronegativity increase from La to Lu.  IONISATION ENTHALPIES OF LANTHANOIDS The first ionisation enthalpies of the lanthanoids are around 600 kJ mol–1. the second IE is about 1200 kJ mol–1 comparable with those of calcium. A detailed discussion of the variation of the third ionisation enthalpies indicates that the exchange enthalpy considerations (as in 3d orbitals of the first transition series), appear to impart a certain degree of stability to empty, half-filled and completely filled orbitals f level. This is indicated from the abnormally low value of the third ionisation enthalpy of lanthanum, gadolinium and lutetium.  OXIDATION STATES OF LANTHANOIDS General trend:The most common oxidation state is M+3. It is because the hydration enthalpy of M+3 compensates for the three ionisation enthalpies. But in case of M+2 , the hydration enthalpy is too less due to less +ve charge and it can not to compensate for the two ionisation enthalpies. Similarly M+4 is also very rre because the 4th ionisation enthalpy is too large.(Almost equal to the sum of first three ionisation enthalpies) However, occasionally +2 and +4 ions in solution or in solid compounds are also obtained.This irregularity arises mainly from the extra stability of empty, half-filled or filled f subshell. THE VARIOUS OXIDATION STATES AND THEIR COLOURS IN AQUEOUS SOLUTIONS  Thus, the formation of CeIV is favoured by its noble gas configuration, but it is a strong oxidant reverting to the common +3 state. The Eo value for Ce4+/ Ce3+ is + 1.74 V which suggests that it can oxidise water. However, the reaction rate is very slow and hence Ce(IV) is a good analytical reagent. Pr, Nd, Tb and Dy also exhibit +4 state but only in oxides, MO2. Eu2+ is formed by losing the two s electrons and its f 7 configuration accounts for the formation of this ion. However, Eu2+ is a strong reducing agent changing to the common +3 state. Similarly Yb2+ which has f 14 configuration is a reductant. TbIV has half-filled f-orbitals and is an oxidant. The behaviour of samarium is very much like europium, exhibiting both +2 and +3 oxidation state.  FORMATION OF COLOURED IONS BY LANTHANOIDS Many trivalent Ln ions are coloured both in the solid state and in aqueous solutions. Colour of these ions may be attributed to the presence of unpaired f electrons. Neither La3+ nor Lu3+ ion shows any colour but the rest do so. However, absorption bands are narrow, probably because of the excitation within f level.(f-f transition) Elements with (n)f electrons often have a similar colour to those with (14 - n)f electrons. However, the elements in other valency states do not all have colours similar to their isoelectronic 3+ counterparts.  Magnetic properties La+3, Ce+4, Lu+3 and Yb+2 have either empty or fully filled 4f, 5d and 6s orbitals so they are diamagnetic in nature. Other trivalent ions which have unpaired electrons in these orbitals, show para magnetism, which is calculated by the following formula: Where g and J have again complicated formulae based on both spin and orbital magnetic moment. In Lanthanoids, the splitting of f orbital due to ligand is very small as f orbitals are well covered by 5s, 5p, 5d and 6s orbitals.(see figure) Therefore, the electrons can almost freely rotate from one to another f orbitals causing orbital magnetic moment. Hence both spin and orbital magnetic moment are considered.  The para magnetism rises to maximum in neodymium. Then it decreases. From Eu it again starts increasing and reaches to maximum in Dysprosium and then again decreases up to Lu Nd is used as powerful magnet which has versatile use in industry. Due to magnetic properties of Gadolinium, it is used in MRI (Magnetic resonance imaging) Samarium- cobalt magnets are used in motors and in military weapons. neodymium. Neodymium Gadolinium Sm + Co  CHEMICAL REACTIVITY OF LANTHANOIDS In their chemical behaviour, in general, the earlier members of the series are quite reactive similar to calcium but, with increasing atomic number, they behave more like aluminium. Values for EV for the half-reaction: Ln3+(aq) + 3e– → Ln(s) are in the range of –2.2 to –2.4 V except for Eu for which the value is –2.0 V. This is, of course, a small variation. Some reactions of lanthanoids are as follows: 1. Reaction with hydrogen gas: The metals combine with hydrogen when gently heated in the gas to form dihydrides and trihydrides. Ln(s) + H2(g) ----------------------> LnH2 At high pressure 2Ln(s) + 3H2(g) ------------------> 2LnH3 2. Reaction with carbon: The carbides, Ln3C, Ln2C3 and LnC2 are formed when the metals are heated with carbon. 3. Reaction with dil acids: They liberate hydrogen from dilute acids Ln(s) + HCl(aq) ---------------> LnCl3 (aq) + H2(g) 4. Reaction with halogens: They burn in halogens to form halides. 2Ln(s) + 3X2(g) ---------------> heat 2LnX3 (aq) 5. Reaction with oxygen: They form oxides M2O3 4M(s) + 3O2(g) -------------> 2M2O3 6. Reaction with water : With water they∆ form hydroxides M(OH)3. The hydroxides are definite compounds, not just hydrated oxides. They are basic like alkaline earth metal oxides and hydroxides. 2Ln + 3H2O -------- Ln2O3 + 3H2 Ln2O3 + 3H2O---------- 2Ln(OH)3 Summary of chemical reactions:  USES OF LANTHANOIDS The best single use of the lanthanoids is for the production of alloy steels for plates and pipes. A well known alloy is mischmetall which consists of a lanthanoid metal (~ 95%) and iron (~ 5%) and traces of S, C, Ca and Al. A good deal of mischmetall is used in Mg-based alloy to produce bullets, shell and lighter flint. mischmetall Mixed oxides of lanthanoids are employed as catalysts in petroleum cracking. Some individual Ln oxides are used as phosphors in television screens and similar fluorescing surfaces.  THE ACTINOIDS The actinoids include the fourteen elements from Th to Lr. The actinoids are radioactive elements and the earlier members have relatively long half-lives. the latter ones have half-life values ranging from a day to 3 minutes for lawrencium (Z =103). The latter members could be prepared only in nanogram quantities. These facts render their study more difficult.  ACTINOIDS: ELECTRONIC CONFIGURATION All the actinoids are believed to have the electronic configuration of 7s2 Configurations and variable occupancy of the 5f and 6d subshells. The fourteen electrons are formally added to 5f, though not in thorium (Z = 90) but from Pa onwards the 5f orbitals are complete at element 103. The irregularities in the electronic configurations of the actinoids, like those in the lanthanoids are related to the stabilities of the f 0, f 7 and f 14 occupancies of the 5f orbitals. Thus, the configurations of Am and Cm are [Rn] 5f 77s2 and [Rn] 5f 76d17s2. Although the 5f orbitals resemble the 4f orbitals in their angular part of the wave-function, they are not as buried as 4f orbitals and hence 5f electrons can participate in bonding to a  IONIC SIZES The general trend in lanthanoids is observable in the actinoids as well. There is a gradual decrease in the size of atoms or M3+ ions across the series. This may be referred to as the actinoid contraction (like lanthanoid contraction). The contraction is, however, greater from element to element in this series resulting from poor shielding by 5f electrons.  OXIDATION STATES OF ACTINOIDS There is a greater range of oxidation states, which is in part attributed to the fact that the 5f, 6d and 7s levels are of comparable energies. The actinoids show in general +3 oxidation state. (same reason as in lanthanides) The elements, in the first half of the series frequently exhibit higher oxidation states. For example, the maximum oxidation state increases from +4 in Th to +5, +6 and +7 respectively in Pa, U and Np but decreases in succeeding elements. The actinoids resemble the lanthanoids in having more compounds in +3 state than in the +4 state. However, +3 and +4 ions tend to hydrolyse. Because the distribution of oxidation states among the actinoids is so uneven and so different for the earlier and latter elements, it is unsatisfactory to review their chemistry in terms of O.N. Oxidation states of actinoids The oxidation states in bold are most stable. +5 ON of Uranium is stable only in solid state. In solutions, it disproportionates to give +4 and +6 O.N. UO2+  U+4 + UO2+2 The divalent ions of actinides behave like Ba+2 ion in chemical behaviour. (In lanthanides, they behave like Ca+2)  IMPORTANT QUESTIONS ON OXIDATION STATE OF ACTINOIDS Q1. Why No+2 is more stable? Ans 1. Due to 5f14 configuration in divalent state Q2. The most stable oxidation state up to uranium is the one involving all the valence electrons. Why? Ans 2. Because they get 5f0 electronic configuration after losing all their valence electrons. Q3. How the higher oxidation states like +6 of lower actinides are stabilized ? Ans 3. +6 oxidation state is possible only with most electronegative fluorine or in oxocations MO2+2  COLOUR OF THE ACTINIDE IONS ectronic transfers between neighbouring atoms)  REACTIVITY OF ACTINOIDS The actinoids are highly reactive metals, especially when finely divided. The action of boiling water on them, for example, gives a mixture of oxide and hydride. Combination with most non metals takes place at moderate temp. HCl attacks all metals but most are slightly affected by nitric acid owing to the formation of protective oxide layers. alkalies have no action.  MAGNETIC PROPERTIES OF THE ACTINIDES The magnetic properties of the actinoids are more complex than those of the lanthanoids. Although the variation in the magnetic susceptibility of the actinoids with the number of unpaired 5f electrons is roughly parallel to the corresponding results for the lanthanoids, the latter have higher values.  IONISATION ENTHALPIES OF ACTINOIDS It is evident from the behaviour of the actinoids that the ionisation enthalpies of the early actinoids, though not accurately known, but are lower than for the early lanthanoids. This is quite reasonable since it is to be expected that when 5f orbitals are beginning to be occupied, they will penetrate less into the inner core of electrons. The 5f electrons, will therefore, be more effectively shielded from the nuclear charge than the 4f electrons of the corresponding lanthanoids. Because the outer electrons are less firmly held, they are available for bonding in the actinoids.  SOME APPLICATIONS OF d- AND f-BLOCK ELEMENTS In construction: Iron and steels are the most important construction materials. Their production is based on the reduction of iron oxides, the removal of impurities and the addition of carbon and alloying metals such as Cr, Mn and Ni. In pigment industry: Some compounds are manufactured for special purposes such as TiO for the pigment industry. In battery industry: MnO2 is manufactured to use it in dry battery cells. The battery industry also requires Zn and Ni/Cd. Precious metals: The elements of Group 11 are still worthy of being called the coinage metals, although Ag and Au are restricted to collection items and the contemporary UK ‘copper’ coins are copper-coated steel. The ‘silver’ UK coins are a Cu/Ni alloy. UK ‘copper’ and ‘silver' coins  In catalysis: Many of the metals and/or their compounds are essential catalysts in the chemical industry. For example: 1. V2O5 catalyses the oxidation of SO2 in the manufacture of sulphuric acid. 2. TiCl4 with Al(CH3)3 forms the basis of the Ziegler catalysts used to manufacture polyethylene (polythene). 3. Iron catalysts are used in the Haber process for the production of ammonia from N2/H2 mixtures. 4. Nickel catalysts enable the hydrogenation of fats to proceed. 5. In the Wacker process the oxidation of ethyne to ethanal is catalysed by PdCl2. In polymerisation processes: Nickel complexes are useful in the polymerisation of alkynes and other organic compounds such as benzene. In photographic industry: The photographic industry relies on the special light-sensitive properties of AgBr. Acknowledgement: Tinto Johns M.Sc. M.Ed. From slideshare.com – slides 3 to 29