Title 5.D-BLOCK & CO-ORDINATION COMPOUNDS_Final ( 109 - 156 ).pdf ✅

NISHITH Multimedia India (Pvt.) Ltd., 109 JEE ADVANCED - VOL - VII JEE MAINS - CW - VOL - I RELATIONS NISHITH Multimedia India (Pvt.) Ltd., d-BLOCK & CO-ORDINATION COMPONDS d-BLOCK & CO-ORDINATION COMPOUNDS SYNOPSIS d-BLOCK 1. Zn, Cd, Hg of group 12 (II B group) are not regarded as transition elements 2. Elements with 5 d configuration:         1 5 2 5 1 5 2 5 Cr : Ar 4s 3d ; Mn : Ar 4s 3d Mo : Kr 5s 4d ;Re Xe 6s 5d 3. Elements with 10 d configuration: 1 10 1 10 0 10 1 10 2 10 1 10 2 10 Cu : 4s 3d Zn 4s 3d Pd 5s 4d Ag : 5s 4d Cd 5s 4d Au : 6s 5d Hg 6s 5d     4. Highest MP in 3d serice : Cr 4d serice : Mo 5d serice :W 5. Enthalpy of atomisation is highest in 3d series : V Enthalpy of atomisation is lowest in 3d series : Zn 6. Mercury is a liquid metal because Hg has   14 10 2 Xe f d s 4 5 6 configuration. Due to poor shielding nature of 4f and 5d orbitals, the 2 6s electrons are tightly held to the atom. This de- creases the extent of delocalization of electrons and decrease the metal - metal bond strength. 7. SIZE OFATOMS AND IONS The covalent radii of the elements decrease from left to right across a row in the transition series, until near the end when the size increase slightly. On passing from left to right, extra protons are placed in the nucleus and extra orbital electrons are added. The orbital electrons shield the nuclear charge incompletely (d electrons shield less effi- ciently than p electrons, which in turn shield less effectively than s electrons). Because of this poor screening by d electrons, the nuclear charge attracts all of the electrons more strongly; hence a contraction in size occure. Atoms of the transition elements are smaller than those of the Group 1 or 2 elements in the same horizontal period. This is partly because of the usual contraction in size across a horizontal period discussed above, and partly because the orbital electrons are added to the penultimate d shell rather than to the outer shell of the atom. 8. Elements with similar size : Fe, Co, Ni Zr, Hf Nb, Ta Mo, W 9. Oxidation states: The transition metals exhibit a large number of oxidation states. With the exception of a few elements, most of these show variable oxidation states. These different oxidation states are related to the electronic configuration of their atoms. The existance of the transition elements in differ- ent oxidation states mean that their atoms can lose different number of electrons. This is due to the participation of inner (n - 1) d- electrons in addition to outer ns-electrons be- cause, the energies of the ns and (n - 1) d-sub- shell are nearly same. For example, scandium has the outer electronic configuration 1 2 3d 4s . It exhibits an oxidation state of +2 when it uses both of its 4s-electrons for bonding but it can also show oxidation state of +3 when it uses its two s-electrons and one d-electron. Similarly, the other atoms can show oxidation states equal to ns-and (n-1) d-electrons. It may be noted that the stability of a given oxi- dation state depends upon the nature of the ele- ments with which the metal is combined. The highest oxidation states are found in com- pounds of fluorides and oxides because fluorine and oxygen are most electronegative elements.
d-BLOCK & CO-ORDINATION COMPONDS 110 NISHITH Multimedia India (Pvt.) Ltd., JEE ADVANCED - VOL - VII NISHITH Multimedia India (Pvt.) Ltd., The examination of the common oxidation states exhibited by different transition metals reveals the following (i) The variable oxidation states of transition met- als are due to participation of inner (n-1) d and outer ns-electrons. The lowest oxidation state corresponds to the number of ns-electrons. For example, in the first transition series, the low- est oxidation states of   5 1 Cr 3d 4s and   10 1 Cu 3d 4s are +1 while for other, it is +2   1 10 2 3d 4s  . (ii) Except scandium, the most common oxida- tion state of the first row transition elements is +2 which arises due to loss of two 4s-electrons. This mean that after scandium 3d-orbitals be- come more stable and therefore, are lower in energy than the 4s-orbitals. As a result, electrons are first removed from 4s-orbitals. (iii) The elements which show the greater num- ber of oxidation states occur in or near the middle of the series. For example, in the first transition series, man- ganese exhibits all the oxidation states from +2 to +7. The lesser number oxidation states in the begining of series can be due to the presence of smaller number of electrons to lose or share (Sc, Ti). On the other hand, at the extreme right hand side end (Cu, Zn), lesser number of oxidation state is due to large number of d electrons so that only a fewer orbitals are available in which the electron can share with other for higher valence. The highest oxidation state shown by any transi- tion metal is +8. (iv) In the +2 and +3 oxidation states, the bonds formed are mostly ionic. In the compounds of higher oxidation states (gen- erally formed with oxygen and fluorine), the bonds are essentially covalent. Thus the bonds in +2 and +3 oxidation states are generally formed by the loss of two or three electrons respectively while the bonds in higher oxidation states are formed by sharing of d-elec- trons. For example, in MnO4  (Mn in +7 state) all the bonds are covalent. (v) Within a group, the maximum oxidation state increase with atomic number. For example, iron (group 8) shows common oxidation states of +2 and +3 but ruthenium and osmium in the same group form compounds in the +4, +6 and +8 oxidation states. (vi) transition metals also form compounds in low oxidation states such as +1 and 0 or negative. The common examples are     4 5   Ni CO , Fe CO       in which nickel and iron are in zero oxidation state. (vii) The variability of oxidation states in transi- tion elements arises because of incomplete filling of the d-orbitals in such a way that their oxida- tion states differ by unity such as II III IV V , V , V and V V . This behaviour is in contrast with the variability of oxidation states of non-transition elements (p- block elements), where oxidation states normally differ by a unit of two such as 2 3 Sn ,In ,In ,    etc. (viii) Unlike p-block elements where the lower oxidation states are favoured by heavier mem- bers (due to inert pair effect), the higher oxida- tion states are more stable in heavier transition elements. For example, in group 6, Mo (VI) and W(VI) are found to be more stable than Cr (VI). There- fore, Cr (VI) in the form of dichromate in acidic medium is a strong oxidising agent where as MoO and WO 3 3 are not. The magnitude of ionization enthalpy gives the amount of energy required to remove electrons to form a particular oxidation state of the metal in a compound. thus, the value of ionisation enthalpies gives information regarding the ther- modynamic stability of the transition metal com- pounds in different oxidation states. Smaller the ionisation enthalpy of the metal, the stable is its compound.
NISHITH Multimedia India (Pvt.) Ltd., 111 JEE ADVANCED - VOL - VII JEE MAINS - CW - VOL - I RELATIONS NISHITH Multimedia India (Pvt.) Ltd., d-BLOCK & CO-ORDINATION COMPONDS For example, the first four ionisation enthalpies of nickel and platinum are given below : Ionisation enthalpies Ni Pt 1 2 IE IE  3 1 2.49 10 kJmol  3 1 2.66 10 kJmol  3 4 IE IE  3 1 8.80 10 kJ mol  3 1 6.70 10 kJmol  Total 3 1 11.29 10 kJ mol  3 1 9.36 10 kJmol  It is clear form the above table that the sum of first two ionization enthalpies is less for nickel than for platinum. 2 3 1 2 3 1 Ni Ni 2e I.E. 2.49 10 kJ mol Pt Pt 2e I.E. 2.66 10 kJ mol               Therefore, ionization of nickel to 2 Ni  is ener- getically favourable as compared to that of plati- num. Thus, the nickel (II) compounds are thermody- namically more stable than platinum (II) com- pounds. On the other hand, the sum of first four icnisation enthalpies is less for platinum than for nickel as : 4 3 1 4 3 1 Ni Ni 2e I.E. 11.29 10 kJ mol Pt Pt 2e I.E. 9.36 10 kJ mol               Thus, the platinum (IV) compounds are relatively more stable than nickel (IV) compounds. Therefore, K PtCl 2 6 [having Pt (IV) is a well- known compound whereas the corresponding nickel compound is not known. However, in solutions the stability of the com- pounds depends upon electrode potentials. 10. Electrode potentials Metals with 0 E ve SRP   liberate H2 from dil.HCl and those with 0 E ve SRP   do not liberate. Zn, Fe, Mn displace H2 from dil.HCl but Cu, Ag, Hg, Au do not displace. Ti V Cr Mn Fe Co Ni Cu Zn   0 2 M M/ E  in volts -1.63 -1.18 -0.91 -0.44 -0.28 -0.25 -0.25 +0.34 -0.76   0 3+ 2+ M /M E (In volts ) -0.37 -0.26 -0.41 +1.57 +0.77 +1.97 11. Stability of the various oxidation states Compounds are regarded as stable if they exist at room temperature, are not oxidized by the air, are not hydrolysed by water vapour and do not disproportionate or decompose at normal tem- peratures. Within each of the transition Groups 3 - 12, there is a difference in stability of the various oxidation states that exist. In general, the second and third row elements exhibit higher coordination numbers, and their higher oxidation states are more stable than the corresponding first row elements. This gives the known oxides and halides of the first, second and third row transition elements. Stable oxidation states from oxides, fluorides, chlorides, bromides and iodides. Strongly reducing states probably do not form fluorides and/or oxides, but may as well form the heavier halides. Conversely, strongly oxidizing states form oxides and fluorides, but not iodides. 12. In 3d series: The element showing highest number of varible oxidation states: Mn The elements which does not show varible oxidation states Sc,Zn(Sc: +3;Zn: +2) 13. The stable highest oxidation state possibel in 3d series elements in their flourides is + 6 (Cr) CrF6  14. The +7 state for Mn is not represented in simple halides but MnO3 F is known, 15. The highest Mn fluoride is MnF4 whereas the highest oxide is Mn2 7 O 16. 2 VO Cr O MnO 2 2 7 4      : oxidising power 17. In 3d series 3+ 3 Mn and Co  ions are the strongest oxidizaing agents in aq. solution. 18. 2 2 2 Ti ,V and Cr    are strong reducing agents and will liberate hydrogen from dilute acids
d-BLOCK & CO-ORDINATION COMPONDS 112 NISHITH Multimedia India (Pvt.) Ltd., JEE ADVANCED - VOL - VII NISHITH Multimedia India (Pvt.) Ltd., 19. In 3d series, of the 4 d species , 2 Cr  is strongly reducing and 3 Mn  is strongly re ducing   2 3 2 3 3 2g Cr to Cr :d tod d half filled t level      3 2 4 5 5 Mn to Mn : d tod d half filled    20. in 3d series , standard electrode potential   2 M / M  value is +ve for copper 21. Many copper (1) compounds are unstable in aq solution and undergo disproportionation 2 2Cu Cu Cu     2 0.15V 0.5V Cu Cu Cu       22. 2 Mn  compounds are more stable than 2 Fe  towards oxidation to their +3 state 23. Acid solution   0.56V 0.27V 2 3 4 4 4 0.93V 0.1V 3 2 0.2V 1.55V 2 MnO MnO MnO MnO Mn Mn OH Mn                 24. 2 MnO4  in acidic medium disproportionate to MnO and MnO 4 2  25. Acid solution: 2 3 1.33V 0.41V 2 7 2 0.91V Cr O Cr Cr Cr          26. Basic solution     2 0.13V 4 3 1.01V 1.4V 2 CrO Cr OH Cr OH Cr        27. DENSITY The atomic volumes of the transition elements are low compared to elements in neighbouring Groups 1 and 2. This is because the nuclear charge is poorly screened and so attracts all the electrons more strongly. In addition, the extra electrons added occupy inner orbitals. Consequently the denities of the transition met- als are high. Practically all have a density greater than 3 5g cm . (The only exceptions are Sc 3.0 3 g cm and Y and Ti 4.5 3 g cm .) The densities of the second row are high and third row values are even higher. The two elements with the highest densities are osmium 22.57 3 g cm and iridium 22.61 3 g cm . 28. Lowest density in 3d serics : Sc highest density in 3d serics : Ni, Cu 29. High density of post lanthanide elements: It is because of unexpectedly smaller size due to lanthanide contraction. r At Wt . d g cc  /  Ag 0 1.44 A 108 10.8 Au 0 1.44 A 196 19.4 30. REACTIVITY OF METALS Many of the metals are sufficiently electroposi- tive to react with mineral acids, liberating H2 . A few have low standard electrode potentials and remain unreactive or noble. Noble character is favoured by high enthalpies of sublimation, high ionization energies and low enthalpies of solvation. The high melting points indicate high heats of sub- limation. The smaller atoms have higher ionization ener- gies, but this is offset by small ions having high solvation energies. This tendency to favour noble character is most pronounced for the platium metals (Ru, Rh, Pd, Os, Ir, Pt) and gold. 31. The metals of the second and third transition se- ries have greater enthalpies of atomisation than the corresponding elements of the first transition series.