D and F Block Elements Notes 2024-25 PDF

d and f -Block Elements Scope : Position in the periodic table, occurrence, electronic configuration and characteristics of transition metals, general trends in properties of the 3d-series of transition metals - metallic character, ionisation enthalpy, oxidation states, ionic radii, colour of ions,...

d and f -Block Elements Scope : Position in the periodic table, occurrence, electronic configuration and characteristics of transition metals, general trends in properties of the 3d-series of transition metals - metallic character, ionisation enthalpy, oxidation states, ionic radii, colour of ions, catalytic property, magnetic properties, interstitial compounds, alloy formation. Lanthanoids and actinoids. (i) d-Block: 3d, 4d and 5d series ;Study in terms of metallic character, atomic and ionic radii, ionisation enthalpy, oxidisation states, variable valency, formation of coloured compounds, formation of complexes, alloy formation. (ii) f-Block: 4f and 5f series ;Electronic configuration, atomic and ionic radii, oxidisation states, formation of coloured compounds, formation of complexes, alloy formation. Lanthanoid contraction and its consequences. Chemical reactivity – with oxygen, hydrogen, halogen, sulphur, nitrogen, carbon and water. Actinoids - oxidation states and comparison with lanthanoids. 13.1 Introduction The periodic table is divided into four blocks, viz., s, p, d and f block after names of the orbital where the last electron enters. The d-block elements are also called transition elements. These elements exhibit a transition between the s-block and p-block elements. These elements come into existence from the fourth period onwards of the periodic table. Successive filling of d-orbitals takes place in the formation of d-block elements. Transition elements may be defined as elements which contain partially filled d-orbitals. Zinc, Cadmium and Mercury are not covered under transition elements because in these cases, the d-orbitals are fully filled. However, customarily, they are kept in the d-block. 13.2 Electronic Configuration of d block elements: (n - 1) d ¹⁻¹⁰ns¹⁻². Electronic Configuration of f block elements: (n-2) f 1-14 (n-1) d 0-1ns0-2 13.2.1 Exceptional Configuration of Cr, Cu Greater stability of half-filled and fully filled d-orbitals can be ascribed to great amount of exchange energy. ₂₄Cr: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹3d⁵ ₂₉Cu: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s¹3d¹⁰ 13.3 PROPERTIES OF TRANSITION ELEMENTS 1)Metallic 1) hard, lustrous, malleable, ductile, and have high melting Character and boiling points, high thermal and electrical conductivity. 2)Transition elements have metallic bonding in them because one or two electrons in the outermost orbit (ns¹ or ns²) are labile.This prompts the formation of metallic bond. Greater the number of unpaired d electrons stronger is the bonding due to overlapping of unpaired electrons between different atoms. Thus Cr, Mo, W are hard metals as they have a large number of unpaired electrons. 3) Enthalpy of atomization of transition elements are very high. Enthalpy of atomization is the energy required to break the force of attraction between atoms. 4)Absence of unpaired electrons, so no – overlapping of unpaired electrons, weaker metallic bonding.Therefore Zn, Cd, and Hg are comparatively soft metals. 2)Ionization The ionization energies of transition elements are higher Energy and than those of s-block elements but lower than p-block Electrode elements. In a particular transition series, ionization energy Potential increases gradually as we move from left to right. However, the relative difference in ionization energy values of any consecutive d-block elements in a particular period is much smaller than those of s- and p-block elements. Explanation: The increase in ionization energy along the series is due to increase in nuclear charge. As the transition elements involve the gradual filling of (n-1) d-orbitals, the effect of increase in nuclear charge is partly cancelled by increase in screening effect. Consequently, in ionization energy along the period of d-block elements is not very significant. It is observed that 5d-transition elements possess higher ionization energies than 3d- and 4d-transition elements. This is due to the greater effective nuclear charge in these elements because of the ineffective shielding of the nucleus by 4f-electrons. The magnitude of ionization energy gives us some estimate of the energy required to raise the metal to a particular oxidation state. From the values of ionization energies of the metals, it is possible to estimate the relative stabilities of various oxidation states of metals. For example, the sums of first two and first four ionization energies of nickel and platinum are given in Table 13.3. We find that the sum of the first two ionization energies is less for nickel; therefore Ni (II) compounds are thermodynamically more stable than Pt (II) compounds. On the other hand, Pt (IV) compounds are more stable than Ni (IV) compounds because sum of first four ionization energies is less for platinum. K₂PtCl₆ is a well known compound of platinum with +4 oxidation state. The corresponding nickel compound is not known. In solutions, besides ionization energy, the other factors that determine the stability of a particular state are the enthalpy of sublimation of the metal and the lattice energy or the solvation energy. From the given flow chart, total enthalpy change, ∆HT for the process M (s) → M⁺(aq) + e⁻is equal to the sum of enthalpy of sublimation of metal, ionization energy of metal and the enthalpy of hydration of the metal ion. ∆HT = ∆HS + I.E. + ∆Hhyd Smaller the value of ∆HT, greater will be the stability of a particular oxidation state of metal in an aqueous solution.The electrode potentials govern the value of ∆HT. The smaller the standard electrode potential (E°red), the more stable is the oxidation state of the metal in the aqueous state. 4. Atomic and The atomic and ionic radii of transition elements lie in Ionic Radii between those s- and p-block elements. Among the elements of the particular transition series, as the atomic number increases, the atomic radii first decrease till the middle, become almost constant and then increase towards the end of the period. For example, the atomic radii of first transition series decrease from Sc to Cr, remain almost constant till Cu and then increase toward the end. Explanation: The decrease in size in the beginning is ascribed to the increase in nuclear charge. However, the increased nuclear charge is partly cancelled by the screening effect of electrons in the d-orbitals of penultimate shell. When the increased nuclear charge and increased screening effect balance each other, the atomic radii become almost constant. Increase in atomic radii towards the end takes place due to electron-electron repulsions. In fact, the pairing of electrons in d-orbitals occurs after d⁵ configuration. The repulsive interactions between the paired electrons in d- orbitals become strong towards the end of the period and result in increased atomic size. The ionic radii also follow the similar trends. The elements of second and third transition series belonging to a particular group have an almost equal atomic radius. This is because of lanthanide contraction (discussed later). For example, atomic radii of Pd and Pt are 137 pm and 138 pm respectively. 5.Oxidation States All transition metals show a great variety of oxidation states. The variable oxidation states of transition elements occur due to the participation of ns and (n-1)d electrons in bonding. The lower oxidation state is generally exhibited when ns-electrons participate in bonding and higher oxidation states are shown when ns and (n-1)d electrons together take part in bonding. 6. Complex Formation Complex compounds are those compounds in which the metal ion is linked to a number of anions and/or neutral molecules having lone pairs of electrons through co-ordinate bonds. These ions/molecules are called ligands. These ligands donate electron pairs to the central atom to form co-ordinate bonds. Transition elements form many co- ordination (complex) compounds. This does not occur in s- and p-blocks elements due to the following reasons. Their tendency to form complexes is due to the following reasons: (i) Small size and high charge density of the ions of transition metals. (ii) Presence of vacant orbitals of appropriate energy which can accept lone pairs of electrons donated by other groups (ligands). (iii) Large effective nuclear charge. Colour of transition–metal compounds The compounds of transition elements are usually coloured. The colour of these compounds is due to the absorption of some radiation from visible light to promote an electron from one of the d-orbitals to another.All the d-orbitals in the transition elements do not possess same energy in their complexes. Under the influence of the ligands attached, the d-orbitals are split into two sets of orbitals (eg and t2g ) having slightly different energies. In the transition elements which have partly filled d-orbitals, the transition of electron takes place from the lower d- orbitals to higher d-orbitals within the same subshell. The energy required for this transition falls in the visible region. So, when white light is incident on these complexes they absorb a particular colour for the promotion of electron and the remaining colours are emitted. The colour of the complex is the colour of emitted radiation. For example, titanium salts are purple in colour. When H₂O molecules (ligands) approach the Ti³⁺ to form the complex compound, five d-orbitals are split into two sets, eg and t2g consisting of three d-orbitals and eg consisting of two d-oribtals. These two sets of d-orbitals belonging to the same shell possess different energies. eg oribtals possess higher energy than the t2g orbitals. In [Ti (H₂O)₆]³⁺, Ti has d¹ configuration and this electron is present in dє orbital in the ground state. When white light is incident on the compound, d¹ electron absorbs yellow light and is promoted to dy orbital. The transmitted light viz., the violet light is the colour shown by the compound. It may be mentioned that the absorbed light and the transmitted light together constitute the white light. Every colour has a complimentary colour. Both the colours mix to form white light. Similarly, the blue colour of copper salts can be explained. These compounds absorb red colour and transmit blue colours. Zn²⁺ and Ti⁴⁺ salts are white because they do not absorb any radiation in the visible region. In such compounds, d-d transitions are not possible because Zn²⁺ has all the d-orbitals fully-filled, whereas in Ti⁴⁺, all the d-orbitals are vacant. Summary : For colored ions – due to the presence of unpaired electrons (partially filled d orbital ), d-d transition takes place. When white light is incident on these complexes they absorb a particular colour for the promotion of electron and the remaining colours are emitted. Zn 2+ , Cd 2+ , Hg 2+ ions are colorless - due to the presence of paired electrons ( completely filled d orbital ) , no d-d transition takes place. Therefore their complexes are colorless. Other than the Zn 2+ , Cd 2+ , Hg 2+ ions – if any ion is colorless – the reason is due to the presence of empty d orbital , no d-d transition takes place. Therefore their complexes are colorless.  Hint : to answer the above concepts – write the electronic configuration and then give the explanation. 7. Formation of A solid solution of transition metals forms alloys on cooling. Alloys The d-block elements have almost similar atomic size. Therefore, one element can take up positions in the crystal lattice of the other. 8. As catalyst Due to (i) variable oxidation state and (ii) vacant d orbitals they can form unstable intermediate complex with the reactants which changes to products. 9. Interstitial The lattice of transition metals contains vacant spaces that compounds can be filled with atoms such as H, C, and N. Interstitial compounds are formed when Hydrogen, Carbon, and Nitrogen atoms become trapped inside the crystal lattice of metals. 10. Magnetic When a magnetic field is applied to substances, mainly two types of magnetic behaviour are observed: diamagnetism and paramagnetism. Diamagnetic properties substances are repelled by the applied field while the paramagnetic substances are attracted. The d- and f- Block Elements attracted very strongly are said to be ferromagnetic. In fact, ferromagnetism is an extreme form of paramagnetism. Many of the transition metal ions are paramagnetic. Paramagnetism arises from the presence of unpaired electrons, each such electron having a magnetic moment associated with its spin angular momentum and orbital angular momentumThe magnetic moment increases with the increasing number of unpaired electrons. Magnetic moment = , where n is the no. of unpaired electrons.  Lanthanides and Actinides Chemical reactivity with halogen 2 La + 3Cl2 -------- 2LaCl3 Lanthanide contraction :Steady decrease of atomic and ionic radii with increase in atomic number and nuclear charge , due to ineffective shielding of f –orbital. Consequences of lanthanide contraction. (i) similarity in properties of second and third row elements (ii) Decrease in the tendency to act as reducing agents. Reason: Due to lanthanoid contraction size decreases from La to Lu , smaller the size of Lu ion – stronger the bond between Lu and H , therefore bond dissociation energy is high , so difficult to break the bond between Lu and H or difficult to release H atom. (iii) Decrease in the basic character of hydroxides. Reason: Due to lanthanoid contraction size decreases from La to Lu , smaller the size of Lu ion – stronger the bond between Lu and OH , therefore bond dissociation energy is high , so difficult to break the bond between Lu and OH or difficult to release OH ion. Compare lanthanoids actinoids Most of their ions are colorless Most of their ions are colored. do not form complexes easily form complexes easily Non radioactive except promethium Radioactive Cannot form oxo cation Cannot form oxo cation Less basic More basic Similarity : Both shows contractions in size and irregular oxidation states. Uses of d and f elements (i) TiO – white pigment in paints (ii) as catalysts (iii) Coinage metals – Cu, Ag , Au (iv) MnO2 in dry cells (v)Ce alloys (Misch metal) in cigarette lighters. Questions : 1) (a) Zinc, Cadmium and Mercury are not considered as transition elements. Give reason. (b) Silver atom has completely filled d-orbitals (4d10) in its ground state, yet it is regarded as a transition element. Because silver has incomplete d-orbital (4d9) in its +2 oxidation state, hence it is a transition element. 2) Write the electronic configuration of d and f block elements ? 3) Most of the transition elements are hard metals. Give reason. 4) Zn, Cd, and Hg are comparatively soft metals. Give reason. 5) There is an increase in density from Sc to Cu. Give reason. Small and irregular decrease in metallic radii coupled with the relative increase in atomic mass. 6) Enthalpy of atomization of transition elements are very high. Give reason? Greater the number of unpaired d electrons stronger is the bonding due to overlapping of unpaired electrons between different atoms, therefore lot of energy is required to break the bond between atoms. 7) Name the element with lowest value of Enthalpy of atomization in 3d series. Give reason. Zinc , Absence of unpaired electrons or Zn has completely filled d orbital , therefore d electrons are not involved in metallic bonding. 8) Most of the Transition elements are paramagnetic. Give reason. Due to the presence of unpaired electrons. [weakly magnetized in the direction of the magnetizing field when placed in a magnetic field] 9) Calculate the magnetic moment of M 2+( Z =27 ) Magnetic moment = , where n is the no. of unpaired electrons. 3.87 BM ( Bohr Magneton )  10)Calculate the number of unpaired electrons in following gaseous ions : Mn 3+ , Cr 3+ , Ti 3+. Which one of these is the most stable in aqueous solution? Ans : Mn 3+ = 4 unpaired electrons Cr 3+ = 3 unpaired electrons Ti 3+ = 1 unpaired electron Cr 3+ is most stable in aqueous solution because it has half filled t2g3 orbital. 11)The E0 value for the Mn 3+ / Mn 2+ couple is much more positive than that for Cr 3+ / Cr2+ couple or Fe 3+ /Fe 2+ couple. Give reason. It is because Mn 2+ is more stable than Mn 3+ due to stable half filled 3d 5 configuration , whereas Cr 3+ ( t2g 3) and Fe 3+ ( 3d 5 ) are more stable than Cr 2+ and Fe 2+ respectively. 12)The atomic radii of first transition series decrease from Sc to Cr, remain almost constant till Cu and then increase toward the end. Explain. 13)Which is more stable Fe 2+ or Fe 3+ ? Why? Ans: Fe 3+ : half filled orbitals are more stable. 14) Fe2+ has smaller radius than Mn2+ ? Why Ans: Fe2+ has higher value of effective nuclear charge. 15) Mn2+ compounds are more stable than Fe 2+ ions. Give reason. Mn2+ compounds are more stable due to half-filled d-orbitals. Fe2+ compounds are comparatively less stable as they have six electrons in their 3d-orbital. So, they tend to lose one electrons (form Fe3+) and get stable 3d5 configuration. 16) Out of Cr 2+ and Cr 3+ , which one is stable in aqueous solution ? Ans: Cr 3+ is stable in aqueous solution- greater hydration enthalpy of Cr3+ due to its small size and higher charge. + 17) (a) Explain why Cu ion is not stable in aqueous solutions. It is because hydration energy of Cu 2+ ion is high due to to its small size and higher charge. That is why Cu2+ is more stable than Cu +ion in aqueous solution. (b) CuI2 is highly unstable. Why ? This is because Cu 2+ oxidises iodide ion(I-) to I2. 18)Calculate the number of unpaired electrons in following gaseous ions : Mn 3+ , Cr 3+ , Ti 3+. Which one of these is the most stable in aqueous solution? Ans : Cr 3+ is most stable in aqueous solution because it has half filled t2g3 orbital 19) Why is Pt(IV) more stable than Ni(IV) ?( K2PtCl6 is a known compound but not the corresponding compound of Ni) Ans : Sum of the first four ionisation energies for Ni is much higher than sum of the first four ionisation energies for Pt …. ie energy required to remove 4 electrons from Pt is much less than the energy required to remove from Ni. 20) Transition elements show variable oxidation state. Give reason. 21) Scandium does not exhibit variable oxidation state. Give reason. Sc : [Ar ] 3d1 4s2 By removing three electrons from its d and s orbital it forms a very stable inert gas configuration. Therefore, after that electron removal there is no such oxidation state is possible. 22 ) Which of the 3d series of the transition metals exhibits the largest number of oxidation states and why ? Manganese exhibits the largest number of oxidation states because it has seven electrons in s as well as in d orbital which can take part in bond formation. 23)Which is a stronger reducing agent Cr 2+ Fe 2+ and why ? Cr 2+ is a stronger reducing agent because it will get oxidized to Cr 3+ which has half filled orbital (t2g 3 ) which is more stable than 3d 5 in Fe 3+. 24)The lowest oxide of transition metal is basic, the highest is acidic. Give reason. In lowest oxidation state, ionic bonds are formed. Metals are electropositive and they form basic oxides. In highest oxidation state, covalent bonds are  formed. Therefore, oxides are acidic. 25) Transition elements can form complexes. Give reason. 26) The compounds of transition elements are usually coloured. Give reason. Ans :The colour of these compounds is due to the absorption of some radiation from visible light to promote an electron from one of the d-orbitals to another.Under the influence of the ligands attached, the d-orbitals are split into two sets of orbitals (called eg and t2g) having slightly different energies.In the transition elements which have partly filled d-orbitals, the transition of electron takes place from the lower d-orbitals to higher d-orbitals within the same subshell. (due to d-d transition ). 27) Copper salts are blue in colour while Zn salts are white. Give reason. Zn2+ has 3d 10 configuration and no unpaired electrons, hence it is colourless, as no d-d transition takes place. Whereas in Cu2+ state which has 3d9 configuration there is one unpaired electron and it undergoes d-d transitions emiting colour.so Cu 2+ salts are blue in colour. 28) Zn²⁺ and Ti⁴⁺ salts are white. Give reason. Ans: d-d transitions are not possible because Zn²⁺ has all the d-orbitals fully-filled, whereas in Ti⁴⁺, all the d-orbitals are vacant. 29) Transition elements can act as catalysts. Give reason. 30) Transition elements can form alloys. Give reason. 31) Transition elements can form interstitial compounds. Give reason. 32) La(OH)3 is more basic than Lu(OH)3. Give reason. 33) Which trivalent cation is largest in lanthanoid contraction ? Lanthanum 34) Formula of the compound whose transition metal is in +7 oxidation state ? KMnO4 35) Actinoids exhibit large number of oxidation states while lanthanoids exhibit only +3 oxidation states. Give reason. Very small energy gap between 5f, 6d and 7s subshells. Thus, the outermost electrons get easily excited to the higher energy levels, giving variable oxidation states. In the case of lanthanoids , due to large energy gap between 4f , 5d and 6s subshells, it is difficult to lose electrons. 36) Zr and Hf exhibit similar properties. Give reason. Zr and Hf exhibit similar properties due to lanthanide contraction. Electrons present in f-subshell doesn’t have good shielding effect due to which with increase in atomic number effective nuclear charge, size gets constricted and thus size of Hf and Zr becomes almost equal and hence both have similar properties. 37) Actinoid contraction is greater from element to element than lanthanoid contraction.why. It is because of poor shielding of 4f and 5f electrons in actinoids , whereas in lanthanoids there is poor shielding effect of 4f electrons only. That is why effective nuclear charge increases more from element to element in actinoids than lanthanoids. 38) What is meant by lanthanide contraction. Mention any 2 consequences.