UNIT 11 CHEMISTRY OF d- ANDf-BLOCK ELEMENTS Structure 11.1 Introduction Objectives 11.2 Transition and Inner Transition Elements - An Introduction 11.3 IUPAC Nomenclature of 6d Transition Series Elements 11.4 .Electronic Configuration of d-Block and f-Block Elements Electronic Configurations of Transition Elements and Ions Electronic Configurations of Lanthanide and Actinide Elements 11.5 Periodic Trends in Properties Atomic Radii and Ioaic Rad~i Melting and Boiling Points Enthalpies of Ionization Oxidation States Colour of the Complexes Magnetic Properties Catalytic Properties Formation of Complexes Formation of Interstitial Compounds (Interstitial Solid Solutions) and Alloys (Substitutional Solid Solutions) 11.6 Summary 11.7 Terminal Questions 11.1 INTRODUCTION In last unit we have studies about the periodicity and representative elements. In this unit we will study the chemistry of d and f block elements. First we will study the IUPAC nomenclature of these elements then we will discuss the electronic configuration, periodicity, variation of size, melting and boiling points. We shall also study the ionization energy, electronegativity, electrode potential, oxidation sate of these elements in detail. Objectives After studying this unit, you should be able to: explain the IUPAC nomenclature of d and f block elements, describe the electronic configuration of d and f block elements, outline the general properties of these elements, and discuss the colour, magnetic complex formation catalytic properties. 1 1.2 TRANSITION AND INNER TRANSITION ELEMENTS - AN INTRODUCTION We already know that in the periodic table the elements are classified into four blocks; namely, s-block, p-block, d-block andfiblock, based on the name of atomic orbital that accepts the valence or differentiating electrons. In the elements of d-block orfiblock the valence electron enters the penultimate (inner to the outermost) (n-l)d orbitals or ante- penultimate (third to the outermost) (n-2lforbitals respectively. The d-block elements occupy position in between s-block andp-block elements and possess properties that are intermediate (or transitional) between elements of s- andp- block and are, therefore, called transition elem'ents. Thef-block elements are often Chemistry of Elements called as inner-transition elements because in these elements the differentiating electron enters thef -orbitals of an inner shell. The term transition is used here because they exhlbit transition element behaviour by exhibiting variable oxidation states, forming coloured ions and exhibiting paramagnetism. The lanthanides (also called lanthanoids or lanthanons) are placed along with lanthanum and actinides (also known as actinoids or actinons) along with actinium in the periodic table. Customarily, they are listed separately in two series at the bottom of the periodic table in order to avoid it being excessively wide. Presently most chemists consider as transition elements, only those elements that, either as free atoms (or neutral atoms) or in any of their common oxidation states, have partly filled d-orbitals. According to this definition, the elements zinc, cadmium and mercury are excluded from the list of transition elements, as they possess completely filled d- orbitals in their neutral atoms and in their common oxidation states (~'3. These large numbers of transition elements are further classified into four series of elements- first transition series, second transition series, third transition series and fourth transition series according to the filling of 3d, 4d, 5d and 6d atomic orbitals. The elements from scandium to copper constitute the first transition series while a group of nine elements from yttrium to silver constitute the second transition series. The third transition series begins with hafnium and goes up to gold. The fourth transition series (also called super heavy elements) starts with element having atomic number 104 and goes up to 1 12. These elements have been synthesized by artificial nuclear reactions and are very unstable with respect to a-decay or spontaneous fission with very short half- lives. Thef-block elements comprise two series of elements- the lanthanide series and the actinide series according to the filling of 4f and Sf orbitals, respectively. A group of fourteen elements following lanthanum in the periodic table are called lanthanides. Si~nilarly,the fourteen elements following actinium in the periodic table are termed as actinide elements. The elements following uranium have been produced artificially and are collectively called transuranium elements. -- - - - - - - - - - - - - - - - - - - 11.3 IUPAC NOMENCLATURE OF 6d TRANSITION SERIES ELEMENTS As we already know each element in the periodic table have been given definite names and their symbols are derived by either taking the first alphabet, or by taking first alphabet and one more alphabet from the name of the elements. But the 4d transition series elements are given special names and symbols according to TUPAC rules, which are given below: 1: The name of the element is directly derived from the atomic number of the element as per the following numerical roots: 0 1 2 3 4 5 6 7 8 9 nil un bi tri quad pent hex sept oct enn 2. These roots are written together in order of appearance of the digits in the atomic number and terminated by -iurn. If enn comes before nil, the last n of enn is elided. Similarly, the final i of bi and tri is omitted when it occurs before -ium. 3. Taking the first letter of the initial roots that make up the number derives the symbols of the elements. ~hus,the name of the elements with atomic numbi 104 will be unnilquadium and the symbol will be Unq. The name and symbol of elen :~tshaving atomic numbers 104-112 are given in Table 1 1.1. Table 11.1: IUPAC names and symbols of fourth transition series elements. Chemistry of d- and .f-Block Elements Atomic Name of Symbol Atomic Name of Symbol Number Element Number Element 104 Unnilquadium Unq 109 Unnilennium Une 105 Unnilpentium Unp 1 10 Ununnilium Uun 106 Unnilhexium Unh 111 Unununium Uuu 107 Unnilseptium Uns 112 Ununbium Uub 108 Unniloctium Uno It is pertinent to note that these IUPAC names are assigned to elements only temporarily till the claimls about their synthesis are confirmed after which they are assigned proper names and symbols. Elements with atomic numbers 109 have already been assigned proper names. Recently the element with atomic number 110 has been named as Darmstadtium (Ds), on 16Ihaugust, 2003 at 42"d General Assembly of IUPAC in Ottawa, Canada. SAQ 1 a) Why zinc, cadmium and mercury are not considered as transition elements? b) Write the rCTPAC name and symbol of unknown elements with atomic number 118, 120and 150. 11.4 ELECTRONIC CONFIGURATION OF I-BLOCK ANDfiBLOCK ELEMENTS In the preceding section we discussed the position of transition elements and the inner transition elements in the periodic table and the rules for naming of elements of fourth transition series. We shall now discuss the ground state electronic configurations of transition and inner transition elements and their ions. 11.4.1 Electronic Configurations of Transition Elements and Ions We already know that the electronic bon figuration of argon atom is id, 2s22p6,3~~3~'. In the atom of next element potassium the differentiating electron enters the 4s level. The 4s level becomes filled at the element calcium, which has the electronic configuration [A-]4s2.In the atoms of successive elements from scandium to zinc, differentiating electrons enter 3d level instead of 4p. The electronic configurations of the atoms of second and third series transition elements follow similar pattern. In atoms of 4d series of transition elements, after filling up of the 5s level at strontium [ICr]5s2 the differentiating electrons enter 4d level instead of 5p. Similarly, in atoms of 5d transition series elements the 6s level is filled at barium and the filling of 5d level begins at lanthanum which intempted by fourteen elements in which the electron enter 4f level (i.e. lanthanides), resumes at hafnium. The resulting electronic configurations of the atoms of transition elements are given in Table 1 1.2. The electronic configuration of the Chemistry of Elements ions can be obtained by removing first the outer ns electrons and then (n-l)d electron of the atom until the number of removed electrons become equal to the charge on the ion. For example, co3+will have electronic configuration as [Ar]3d6 and ~i~'as [Ar]3d, etc. Table 11.2: Electronic configurations of the free atoms of transition elements. it transition series Second transition series Element Free atom Element Free atom F [Ar]3d14s' Y [ICr]4d15s2 [Ar]3d24s' Zr [Kr]4d25s2 [Ar]3d34s' Nb [Kr]4# 5s' [Ar]3ds 4s' Mo [Kr]4ds 5s' [Ar]3ds 4s' b Tc [Kr]4d6 5s' [Ar]3d6 4s2 Ru [Kr]4d75s' [Ar]3d74s2 Rh [Kr]4d5s1 [~r]3d4s~ Pd [Kr14d'~5s' [Ar]3d1° 4s' Ag [Kr14d'~5s' [~r]3d"4s2 Cd [~r]4d'O52 Third transition series I ~ourthtransitionseries I Element Free atom Element Free atom La rxel5d1 6s2 Unq [Rn]5f4 6d7s2 Hf ,U~P [Rn]5f4 6d3 7s' Ta unh lRn15f 6# 7s' W Uns 687s2 Re Uno [Rn]5f4 6d6 7s' 0s Une [Rn]5f4 6d7 7s' Ir Unn [Rn]5f4 627s' Pt Uuu [Rn]5f 6d7s2 Au Uub lRn15f 6dI0 7s' Now you may be wondering as to why the ns level is filled first before the (n-l)d or the (n-22flevels and then later why (n-l)d or (n-22flevels are filled prior to np level. It is the radial dependence of the d-orbitals that is responsible for this order of filling of electrons in these elements. The stability of an electron in various atomic orbitals can be evaluated by comparison of radial probability functions 4n22 T 2 . The plot of radial distribution functions for 3d and 4s electrons is shown in Fig.