d - and

1 The d- block of the periodic table contains the elementsof the groups 3-12 in which the d orbitals areprogressively filled in each of the four long f- block consists of elements in which 4 f and 5 forbitals are progressively filled. They are placed in aseparate panel at the bottom of the periodic table . Thenames transition metals and inner transition metalsare often used to refer to the elements of d-andf-blocks are mainly four series of the transition metals,3d series (Sc to Zn), 4d series (Y to Cd), 5d series (Laand Hf to Hg) and 6d series which has Ac and elementsfrom Rf to Cn. The two series of the inner transitionmetals; 4f (Ce to Lu) and 5f (Th to Lr) are known aslanthanoids and actinoids the name transition metals was derivedfrom the fact that their chemical properties weretransitional between those of s and p- block according to IUPAC, transition metals are definedas metals which have incomplete d subshell either inneutral atom or in their ions.

2 Zinc, cadmium andmercury of group 12 have full d10 configuration in theirground state as well as in their common oxidation statesand hence, are not regarded as transition , being the end members of the 3d, 4d and 5dtransition series, respectively, their chemistry is studiedalong with the chemistry of the transition presence of partly filled d or f orbitals in theiratoms makes transition elements different from that ofThe d - and f - block ElementsThe d- and f- block ElementsAfter studying this Unit, you will beable to learn the positions of the d andf- block elements in the periodictable; know the electronic configurationsof the transition (d- block ) and theinner transition (f- block ) elements; appreciate the relative stability ofvarious oxidation states in termsof electrode potential values; describe the preparation,properties, structures and usesof some important compoundssuch as K2Cr2O7 and KMnO4; understand the generalcharacteristics of the d andf block elements and the generalhorizontal and group trends inthem.

3 Describe the properties of thef- block elements and give acomparative account of thelanthanoids and actinoids withrespect to their electronicconfigurations, oxidation statesand chemical , copper, silver and gold are among the transition elements thathave played important roles in the development of human inner transition elements such as Th, Pa and U are provingexcellent sources of nuclear energy in modern non-transition elements. Hence, transition elementsand their compounds are studied separately. However,the usual theory of valence as applicable to the non-transition elements can be applied successfully to thetransition elements precious metals such as silver, gold andplatinum and industrially important metals like iron,copper and titanium belong to the transition metals this Unit, we shall first deal with the electronicconfiguration, occurrence and general characteristics oftransition elements with special emphasis on the trendsin the properties of the first row (3d) transition metalsalong with the preparation and properties of someimportant compounds.

4 This will be followed byconsideration of certain general aspects such as electronicconfigurations, oxidation states and chemical reactivityof the inner transition TRANSITION ELEMENTS (d- block )The d block occupies the large middle section of the periodic tableflanked between s and p blocks in the periodic table . The d orbitalsof the penultimate energy level of atoms receive electrons giving rise tofour rows of the transition metals, , 3d, 4d, 5d and 6d. All theseseries of transition elements are shown in table general the electronic configuration of outer orbitals of these elementsis (n-1)d1 10ns1 2. The (n 1) stands for the inner d orbitals which mayhave one to ten electrons and the outermost ns orbital may have oneor two electrons. However, this generalisation has several exceptionsbecause of very little energy difference between (n-1)d and ns , half and completely filled sets of orbitals are relativelymore stable.

5 A consequence of this factor is reflected in the electronicconfigurations of Cr and Cu in the 3d series. For example, consider thecase of Cr, which has 3d5 4s1 configuration instead of 3d44s2; theenergy gap between the two sets (3d and 4s) of orbitals is small enoughto prevent electron entering the 3d orbitals . Similarly in case of Cu, theconfiguration is 3d104s1 and not 3d94s2. The ground state electronicconfigurations of the outer orbitals of transition elements are given inTable in thePosition in thePosition in thePosition in thePosition in thePeriodic TablePeriodic TablePeriodic TablePeriodic TablePeriodic the d-Blockof the d-Blockof the d-Blockof the d-Blockof the d-BlockElementsElementsElementsElementsE lementsScTiVCrMnFeCoNiCuZnZ2122232425262 72829304s22212222123d1235567810101st SeriesTable : Electronic Configurations of outer orbitals of the Transition Elements(ground state)2022-23217 The d- and f- block ElementsThe electronic configurations of outer orbitals of Zn, Cd, Hg and Cnare represented by the general formula (n-1)d10ns2.

6 The orbitals inthese elements are completely filled in the ground state as well as intheir common oxidation states. Therefore, they are not regarded astransition d orbitals of the transition elements protrude to the periphery ofan atom more than the other orbitals ( , s and p), hence, they are moreinfluenced by the surroundings as well as affect the atoms or moleculessurrounding them. In some respects, ions of a given dn configuration(n = 1 9) have similar magnetic and electronic properties. With partlyfilled d orbitals these elements exhibit certain characteristic propertiessuch as display of a variety of oxidation states, formation of colouredions and entering into complex formation with a variety of transition metals and their compounds also exhibit catalyticproperty and paramagnetic behaviour.

7 All these characteristics havebeen discussed in detail later in this are greater similarities in the properties of the transitionelements of a horizontal row in contrast to the non-transition , some group similarities also exist. We shall first study thegeneral characteristics and their trends in the horizontal rows(particularly 3d row) and then consider some group SeriesYZrNbMoTcRuRhPdAgCdZ39404142434445 4647485s22111110124d12456781010103rd SeriesLaHfTaWReOsIrPtAuHgZ57727374757677 7879806s22222221125d123456791010 AcRfDbSgBhHsMtDsRgCnZ8910410510610710810 91101111127s22222222126d1234567810104th SeriesOn what ground can you say that scandium (Z = 21) is a transitionelement but zinc (Z = 30) is not?On the basis of incompletely filled 3d orbitals in case of scandium atomin its ground state (3d1), it is regarded as a transition element.

8 On theother hand, zinc atom has completely filled d orbitals (3d10) in itsground state as well as in its oxidised state, hence it is not regardedas a transition numberIntext QuestionIntext QuestionIntext QuestionIntext QuestionIntext atom has completely filled d orbitals (4d10) in its ground can you say that it is a transition element?We will discuss the properties of elements of first transition seriesonly in the following PropertiesNearly all the transition elements display typical metallic propertiessuch as high tensile strength, ductility, malleability, high thermal andelectrical conductivity and metallic lustre. With the exceptions of Zn,Cd, Hg and Mn, they have one or more typical metallic structures atnormal ofProperties ofProperties ofProperties ofProperties ofthe Transitionthe Transitionthe Transitionthe Transitionthe TransitionElementsElementsElementsElemen tsElements(d- block )(d- block )(d- block )(d- block )(d- block )(bcc = body centred cubic; hcp = hexagonal close packed;ccp = cubic close packed; X = a typical metal structure).

9 Fig. :Tr ends in melting points oftransition elementsThe transition metals (with the exceptionof Zn, Cd and Hg) are very hard and have lowvolatility. Their melting and boiling points arehigh. Fig. depicts the melting points oftransition metals belonging to 3d, 4d and 5dseries. The high melting points of these metalsare attributed to the involvement of greaternumber of electrons from (n-1)d in addition tothe ns electrons in the interatomic metallicbonding. In any row the melting points of thesemetals rise to a maximum at d5 except foranomalous values of Mn and Tc and fallregularly as the atomic number have high enthalpies of atomisation whichare shown in Fig. The maxima at aboutthe middle of each series indicate that oneunpaired electron per d orbital is particularlyLattice Structures of Transition MetalsScTiVCrMnFeCoNiCuZnhcphcpbccbccXbc cccpccpccpX(bcc)(bcc)(bcc, ccp)(hcp)(hcp)(hcp)YZrNbMoTcRuRhPdAgCdhc phcpbccbcchcphcpccpccpccpX(bcc)(bcc)(hcp )LaHfTaWReOsIrPtAuHghcphcpbccbcchcphcpcc pccpccpX(ccp,bcc)(bcc)2022-23219 The d- and f- block Elementsfavourable for strong interatomic interaction.

10 In general, greater thenumber of valence electrons, stronger is the resultant bonding. Sincethe enthalpy of atomisation is an important factor in determining thestandard electrode potential of a metal, metals with very high enthalpyof atomisation ( , very high boiling point) tend to be noble in theirreactions (see later for electrode potentials).Another generalisation that may be drawn from Fig. is that themetals of the second and third series have greater enthalpies ofatomisation than the corresponding elements of the first series; this is animportant factor in accounting for the occurrence of much more frequentmetal metal bonding in compounds of the heavy transition ends in enthalpiesof atomisation oftransition elementsIn general, ions of the same charge in a given series show progressivedecrease in radius with increasing atomic number.