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Ch.45 notes – P.1 Ch.45 – Transition metals A. General features of d-block elements 1. Meaning of transition elements * First transition series : Atomic No. 21 22 23 24 25 26 27 28 29 30 Symbol * Electronic configurations of elements in first transition series : At. no. Name Inner shell 21 Scandium 1s22s22p63s23p6 22 Titanium 1s22s22p63s23p6 23 Vanadium 1s22s22p63s23p6 24 Chromium 1s22s22p63s23p6 25 Manganese 1s22s22p63s23p6 26 Iron 1s22s22p63s23p6 27 Cobalt 1s22s22p63s23p6 28 Nickel 1s22s22p63s23p6 29 Copper 1s22s22p63s23p6 30 Zinc 1s22s22p63s23p6 3d 4s * The d-block element is so called because its members have atoms with electronic configurations in which the d-orbitals are being filled. * Sometimes, d-block elements or transition elements are also defined as elements which form compounds in which there is an ______________ ________ subshell of d electrons in at least one of its compounds. (Such definition effectively excludes scandium and zinc from the list of transition elements.) Ch.45 notes – P.2 2. Transition elements as metals * d-electrons are involved in the metallic bond formation in the case of transition metals, therefore they have s-block metals. metallic bond than Such characteristics make transition metals extremely useful as structural metals. * The _______________________ of the transition metals make it possible for atoms of one element to replace those of another element in the formation of alloys . It is possible to make alloys containing transition elements in a wide range of composition. The solid structure is slightly deformed but this is sufficient to modify the physical properties of the structural material, e.g., manganese is well-known for conferring hardness and wear resistance to its alloys, and chromium is responsible for conferring passivity on stainless steels. * Some uses of transition metals Titanium is used in the construction of the hull of the space shuttle and aircraft Coinage metal is an alloy of copper and nickel. The bumpers of vehicles are chromium plated, giving shiny appearance. Pure titanium is not rejected by the body and has been used in replacing missing human teeth with great success. Copper is used for cooking ware, electrical cables and water pipes. Iron is the most important structural metal ever used Ch.45 notes – P.3 3. Comparison of some properties of d-block and s-block metals a) Atomic radii * Variation of atomic radius with atomic number : C.C.Lee/196 (3 inches) * Atomic radii (nm) s-block Li Be 0.152 0.112 Na Mg 0.190 0.160 K Ca d-block Sc Ti V Cr Mn Fe Co Ni Cu Zn 0.235 0.197 0.164 0.147 0.135 0.130 0.135 0.126 0.125 0.125 0.128 0.137 Rb Sr 0.248 0.215 Cs Ba 0.267 0.222 Ch.45 notes – P.4 * Two features : (1) d-block metals generally have atomic radii than s-block metals. (2) d-block metals show considerable ________________ in atomic radius across the series. As one looks at the trend of variation in greater details, it can be seen that the atomic radii of the elements at first _____________ , then remain ____________ in the middle of the series. At the end of the series, the atomic radii actually ____________again. At the beginning of the series, the increase in __________ _______________ with atomic number pulls in the electron cloud, resulting in a reduction of atomic size. Since electrons are added to an inner d subshell across the series, this adds to the primary ______________ and ___________________ of the 3d subshell, so that the effective nuclear charge increases only very slowly in the middle of the row. As a result, there is little change in atomic radii in the middle range. Towards the end of the series, the screening and repulsive effects of the 3d electrons reach a maximum, resulting in an _______________ of the electron cloud. b) Densities * Values of densities of s-block and d-block metals (in g cm-3) s-block Li Be 0.53 1.850 Na Mg 0.97 1.75 K Ca 0.86 1.55 3.00 4.50 6.11 7.14 7.43 7.87 8.90 8.91 8.95 7.14 Rb Sr 1.53 2.54 Cs Ba 1.87 3.60 d-block Sc Ti V Cr Mn Fe Co Ni Cu Zn Ch.45 notes – P.5 * Densities of d-block metals are much than those of s-block metals because (1) d-block metals have ______________ atomic sizes (2) d-block metals have _________________ structures c) Melting points and hardness * Melting points / ℃ s-block * d-block K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn 64 850 1540 1675 1900 1890 1240 1535 1492 1453 1083 420 Melting points and hardness of d-block metals are _____________ than s-block metals because (1) the atomic radii relatively (2) d-block metals usually have of d-block metals are . a ______________ metallic lattice structure. (3) _______________ electrons (including 4s and 3d electrons) are involved in the metallic bond formation. d) Ionization enthalpies Ch.45 notes – P.6 * The first ionization enthalpies of the d-block metals are ___________ than those of s-block metals, since the atomic radii of d-block metals are ____________. * The second ionization enthalpies of the d-block metals are ________ than Group I metals but still __________ than Group II metals. * The third ionization enthalpies of d-block metals are _________ than those of s-block metals, which the electrons are removed from the ___________________. * Along the d-block metals, some abnormally high I.E. may be found: (1) First I.E. of _____. (2) Second I.E. of _____ and _____ . (3) Third I.E. of _____. (4) Fourth I.E. of _____. Ch.45 notes – P.7 e) Electronegativities * Variation of electronegativities among the s-block metals and the d-block metals : s-block Li Be 1.0 1.6 Na Mg 0.9 1.3 K Ca 0.8 1.0 Rb Sr 0.8 1.0 Cs Ba 0.8 0.9 * Sc 1.4 Ti 1.5 V 1.6 Cr 1.6 d-block Mn Fe 1.5 1.8 Co 1.8 Ni 1.8 Cu 1.9 E.N. of d-block metals are______________ than those of s-block metals due to difference in _________________________. f) Reactions with water * s-block metals reacts vigorously with water giving hydrogen gas. d-block metals in general react only very slowly with cold water. * M(s) M(g) Mn+(g) Mn+(aq) d-block metals are less reactive than s-block metals because g) (1) d-block metals have (2) d-block metals have metallic bond I.E. Oxidation state * Except Groups IIIB (e.g. Sc) and Groups IIB (e.g. Zn), all d-block metals exhibit _____________ oxidation states; while this is not the case for the s-block metals. i) Colour * d-block compounds are often ____________; while s-block compounds are _______________. Zn 1.7 Ch.45 notes – P.8 B. Variable oxidation states of d-block elements 1. Oxidation states of the first row transition elements Sc Ti V Cr Mn Fe Co Ni Cu Zn +1 +3 +2 +2 +2 +2 +2 +2 +2 +2 +3 +3 +3 +3 +3 +3 +3 +3 +4 +4 +4 +4 +4 +4 +4 +5 +5 +5 +5 +5 +6 +6 +6 +2 +7 * Because the 3d and 4s electrons are of ___________ energy, both levels of electrons are available for bonding. There is only a ____________________ in successive ionization energies of the d electrons. Thus when elements of the first transition series react to form compounds, they can form ions of roughly the ___________________ by losing different numbers of electrons. * The higher oxidation states arise through ____________ bonding with more electronegative elements such as fluorine, chlorine and oxygen, as in TiCl4 , - CrO3 , MnO4 . 2. Oxidation states of vanadium * Vanadium forms four important oxidation states in aqueous solution. VO3-(aq) VO2+(aq) VO2+(aq) V3+(aq) Fig. 43-6 V2+(aq) Ch.45 notes – P.9 * Electrode potential values of interconversions between different oxidation states of vanadium: ( ) ( ) ( VO2+ VO2+ + 1.0 V ) ( V3+ + 0.36 V ) ( V2+ - 0.25 V ) V - 1.2 V * Example: Refer to the following electrode potential – oxidation state chart and electrode potential values. a) What would be the final vanadium containing product if acidified ammonium metavanadate solution (contains VO2+) is mixed with 1) potassium iodide solution. 2) potassium bromide solution.. 3) copper powder. 4) excess aqueous sulphur dioxide. b) In practice, the product obtained in (4) is blue rather than violet, Explain. Ch.45 notes – P.10 3. Oxidation states of manganese * The following table summarizes the species containing manganese at various oxidation states: Ion/Compound MnO4- Mn(OH)3 Mn2+ MnO42- MnO2 Oxidation state Colour Fig. 43-7 * Electrode potential values of interconversions between different oxidation states of manganese in acidic medium: ( MnO4- ) ( ) ( MnO42+ 0.56 V ) ( Mn3+ MnO2 + 2.26 V ) ( + 0.95 V ) ( Mn2+ + 1.51 V ) Mn - 1.18 V +1.23V + 1.69 V + 1.51 V * Electrode potential values of interconversions between different oxidation states of manganese in alkaline medium : ( MnO4- ) ( ) ( MnO42+ 0.56 V MnO2 + 0.60 V ) ( ) ( Mn(OH)3 - 0.20 V ) ( Mn(OH)2 + 0.10 V ) Mn - 1.55 V + 0.59 V * In acidic medium, ____________________ is very stable in the form of Mn2+. It can be formed when manganese in any higher oxidation is reduced in acidic medium. Ch.45 notes – P.11 * Both __________ and ____________ are powerful oxidizing agents in acidic medium to give Mn2+. MnO2(s) + HCl(aq) MnO4-(aq) + Fe2+(aq) + H+(aq) * In alkaline medium, however, the oxidizing power of MnO4- ion decreases, and its is reduced to __________ only. * Example: 1. Explain whether the following reaction is feasible or not: a) Mixing of Mn(VII) compounds with Mn(IV) compounds to form Mn(VI) compounds in acidic medium. 2 MnO4- + MnO2 + 2 H2O 3 MnO42- + 4 H+ b) Mixing of Mn(VII) compounds with Mn(IV) compounds to form Mn(VI) compounds in alkaline medium. 2 MnO4- + MnO2 + 4 OH- 3 MnO42- + 2 H2O c) Mixing of Mn(II) compounds with Mn(IV) compounds to form Mn(III) compounds in acidic medium. Mn2+ + MnO2 + 4 H+ 2 Mn3+ + 2 H2O Ch.45 notes – P.12 2. This question is concerned with the following electrode potentials: a) Which of the above electrode potentials are dependent on pH? b) Mn3+(aq) in neutral solution will disproportionate, write an equation for this and explain why it is feasible. C. Complex formation by d-block elements 1. Formation of complex ions/compounds * A complex is formed when a transition metal atom (or ion) is surrounded by a number of molecules or ions. They are linked together by ________ covalent bond. e.g. * The transition metal atom (or ion) is called the _____________ ( or nuclear atom ). It must possess _____________ orbitals available for dative bond formation. * The molecules or ions to which the central atom is bonded are called ___________. They must possess ______________ of electrons. * Ligands may be _____________ or tridentate , tetradentate , hexadentate _______________,i.e. bidentate , , etc. Ch.45 notes – P.13 * The number of ligands bonded to the central atom is called ______________ ___________. * The overall charge of the complex depends on the charges of the central atom and the liqands, if any. Co2+ e.g. + 6 H2O Fe3+ + 6 NH3 Fe2+ + 6 CN- Cu2+ + 4 NH3 4 Cl- Cu2+ Co3+ + + 3 NH3 + 3 Cl- * The strong tendency for the d-block metals to form such a large number of stable complexes is due to two reasons: (1) The ________ sizes and ________ charges of their ions. (2) The availability of vacant _____________________________ to accept lone pair electrons from ligands. 2. Nomenclature of complex compounds * [Rules] (1) The cation is always named before the anion, no matter which part of the compound is the actual complex. (2) In naming the complex, the ligands are named before the central atom, and immediately following the central atom is its oxidation state in Roman numerals enclosed in brackets. Ch.45 notes – P.14 (3) Names of some ligands : ClBrOHCNNH3 H2O CO (4) The number of each type of ligand is specified by the Greek prefixes, mono- , di- , tri- , tetra- , penta- and hexa- etc. (5) For more than one type of ligands, they are arranged in the order of anionic - neutral - cationic. (6) For ligands of the same type, they are arranged in the alphabetical order of the element symbols of the ligating atoms. (7) Names for anionic complexes end in 'ate' followed by Roman numerals indicating the oxidation state of the central atom. Metal Name in Anionic Complex Titanium Chromium Manganese Iron Cobalt Nickel Copper Zinc Platinum (8) Names for cationic complexes have no special ending. (9) For a neutral complex compound, the name of the complex is the name of the compound. Ch.45 notes – P.15 * [Examples] [ Co(H2O)6 ]2+ [ Co(H2O)6 ] Cl2 [ Cu(NH3)4 ]2+ [ CoCl2(NH3)4 ]+ [ Fe(NH3)3 (H2O)3 ]2+ [ PtCl(NH3)5 ] Br [ Fe(CN)6 ]3[ Fe(CN)6 ]4K4 [ Fe(CN)6 ] [ CuCl4 ]2[ PtCl6 ]2[ CoCl3(NH3 )3] [ Ni(CO)4] * Ex. 1. Write the formulae of the following compounds: a) chloropentaamminecobalt(III) chloride b) ammonium hexachlorotitanate(IV) c) dihydroxotetraaquairon(II) 2. Name the following compounds: a) [Fe(H2O)6]Cl2 b) [Cu(NH3)4]Cl2 c) [PtCl4(NH3)2] d) K2[CoCl4] Ch.45 notes – P.16 3. Stereochemistry of complexes a) Stereo-structures of complexes (i) Tetrahedral structure * Tetra-coordinated * e.g. * [ Hybridization ] : * Not common for transition metals [ Zn(NH3)4 ]2+ , [ CoCl4 ]2- (ii) Square planar structure * Tetra-coordinated * e.g. * [ Hybridization ] : [ Cu(NH3)4 ]2+ , [ NiCl4 ]2- (iii) Octahedral structure * Hexa-coordinated * e.g. * [ Hybridization ] : [ Co(NH3)6 ]2+ , [ Fe(CN)6 ]3- , Ch.45 notes – P.17 b) Isomerism (i) Structural isomerism * e.g. * e.g. (ii) Geometrical isomerism * e.g. [ Pt Cl2 (NH3)2 ] * e.g. [ Co Cl2 (NH3)4 ]+ * e.g. [ Co Cl3 (NH3)3 ] Ch.45 notes – P.18 4. Stability of complexes * Some ligands may form stronger bonds than other ligands with a particular metal ion.The better ligand will displace the poorer one : [ M (H2O)n ] e.g. nL [ Cu(H2O)4 ]2+ + K st * The + [ M Ln ] 4 NH3 [ Cu(NH3)4 ]2+ + n H 2O + 4 H2O of [ Cu(NH3)4 ]2+ = equilibrium constant for this reaction is known as the _______________________. * The larger the value of K , the st * Some values of stability constants : stable the complex is. Table 43-14 * The values of Kst are generally large. Thus, the complex ions of d-block metals are generally very stable. * Ex.: Ch.45 notes – P.19 D. Coloured ions of d-block elements * The majority of transition metal ions are coloured. The colours and the number of 3d electrons present in some hydrated ions are given below. Fig. 43-10,11 Sc3+(aq) Colourless 3d0 Fe3+(aq) Yellow 3d5 Ti3+(aq) Purple 3d1 Fe2+(aq) Green 3d6 V3+(aq) Green 3d2 Co2+(aq) Pink 3d7 Cr3+(aq) Violet 3d3 Ni2+(aq) Green 3d8 Mn3+(aq) Red 3d4 Cu2+(aq) Blue 3d9 Mn2+(aq) Pink 3d5 Zn2+(aq) Colourless 3d10 * Complex ions of the same central atom but different ligands have different colours. Colours of various complex ions formed by copper(II) ion are listed below : * * [ Cu(H2O)4 ]2+ Blue [ Cu(NH3)4 ]2+ Deep blue [ CuCl4 ]2- Yellow The colour of transition metal complex ion is associated with : (1) an _________________________ (between 1 and 9 (2) the nature of ______________ surrounding the central atom. d A free, isolated transition metal ion has originally all its five electrons) 3d orbitals energetically equivalent, i.e. they are said to be _________________ . * Under the influence of a ligand (such as water molecule), the 3d split into two groups with slightly different energy levels. orbitals are Ch.45 notes – P.20 * As sufficient light energy is absorbed from a white light source, the is promoted from its lower to one of the higher 3d orbitals. 3d electron The resulting d-d transition causes ____________________, and the remainder of the light reflected in the visible spectrum accounts for the specific colour of that complex ion. (The absorbed energy is dispersed as heat, NOT re-emitted as light.) E. Catalytic properties of d-block elements and their compounds 1. Catalysts in industrial processes * V2O5 in Contact process * Finely divided iron powder in Haber process * MnO2 in the decomposition of hydrogen peroxide * Ni or Pt in hydrogenation of alkenes 2. Mechanism of catalytic action a) Heterogeneous catalysis * The reactants of the reaction and the catalysts are of e.g. Fe powder used in Haber process N2(g) * _______________. + 3 H2(g) ==== 2 NH3(g) In the presence of a solid catalyst, at least one of the reacting gases is ________________on the solid surface, hence local concentrations are increased. The adsorption also leads to ________________ of the bonds in the molecules concerned. (Such weakening of the bonds in the reactant molecules results in the _________________________ of the reaction and makes the reaction faster). After formation, the products are ______________ from the surface of the solid catalyst. * The larger number of valence electrons and available orbitals in the atoms of d-block elements facilitate the adsorption of reactants onto their surfaces. Ch.45 notes – P.21 b) Homogeneous catalysis * The catalyst, reactants and products are uniformly distributed in the _____________________. * During catalysis of this type, the reaction takes place via a ______________________ consisting of two steps of which the activation energies are lowered so the reaction is accelerated. * When a transition metal compound is added to a system of a redox reaction, it is converted from one oxidation state to another and then reverted to its original oxidation state. e.g. Given: Fe(II) or Fe(III) used to catalyse the reaction : S2O82- * + 2 I- 2 SO42- + I2 Transition elements and their compounds are good catalysts of this type because they exhibit ___________________________ and enable the redox reactions to take place via two steps.