CLASS 12 CHEMISTRY STUDY MATERIAL (d&f BLOCK ELEMENTS) (1).pdf

Prepared By Dr.S.Vasudhevan, PGT Chemistry PM SHRI Kendriya Vidyalaya No.2, AFS, Tambaram. Chennai Region.  d AND f BLOCK ELEMENTS INTRODUCTION: d block elements are present from fourth period onwards there are mainly three series of th...

Prepared By Dr.S.Vasudhevan, PGT Chemistry PM SHRI Kendriya Vidyalaya No.2, AFS, Tambaram. Chennai Region.  d AND f BLOCK ELEMENTS INTRODUCTION: d block elements are present from fourth period onwards there are mainly three series of the transition metals, 3d series (Sc to Zn), 4d series (Y to Cd) and 5 d series (La to Hg omitting Ce to Lu). d block elements are also known as transition elements. Electronic configuration of the d block elements is (n-1)d1-10 ns 1-2 but Zn, Cd, Hg are d block elements, but not transition metals because these have completely filled d orbitals in its atomic and ionic state. GENERAL PROPERTIES OF THE TRANSITION ELEMENTS 1. ATOMIC AND IONIC RADII: In transition metals, left to right net nuclear charge increases due to poor shielding effect. Due to this, the atomic and ionic radii for transition elements for a given series show a decreasing trend is between the s block and p block elements. Hf and Zr are having same size due to lanthanoid contraction. 2. ENTHALPIES OF ATOMISATION Transition elements exhibit higher enthalpies of atomization because of large number of unpaired electrons in their atoms they have stronger interatomic interaction and hence stronger bond. 3. IONISATION ENTHALPIES In a series from left to right, ionization enthalpy increases due to increase in nuclear charge. The irregular trend in the first ionization enthalpy of the 3d metals, through of little chemical significance, can be accounted for by considering that the removal of one electron alters the relative energies of 4s and 3d orbitals. 4. OXIDATION STATES Transition metals shows variable oxidation state due to incomplete outermost shells. Only stable oxidation states of the first row transition metals are Sc(+3), Ti(+4), V(+5), Cr(+3,+6), Mn(+2,+7), Fe(+2,+3), Co(+2,+3)Ni(+2), Cu(+2) and Zn(+2). The transition in their lower oxidation states (+2 & +3) usually forms ionic compounds. In higher oxidation state compounds are normally covalent. Only Os and Ru show +8 oxidation states in their compounds. Ni and Fe in Ni(CO)4 and Fe(CO)5 show zero oxidation state. 5. TRENDS IN THE STANDARD ELECTRODE POTENTIALS The standard reduction potentials of divalent ions of 3d series generally becomes more and more positive from L to R. Variations occur at V2+,Mn2+ and Zn2+. This is due to less enthalpies of atomization of Mn and V and irregular variations of sum of first two ionization enthalpy terms. The unique behaviour of Cu, having a positive Eo value, accounts for its inability to liberate H2 from acids. Only oxidising acids (nitric and hot concentrated sulphuric) react with Cu, the acids being reduced. The high energy to transform Cu(s) to Cu2+(aq) is not balanced by its hydration enthalpy. 6. TRENDS IN STABILITY OF HIGHER OXIDATION STATES: The higher oxidation number are achieved in TiX4, VF5 and CrF6. The +7 state for Mn is not represented in simple halides but MoO3F is known and beyond Mn no metal has a trihalide except FeX3 and CoF3. The ability of fluorine to stabilise  the highest oxidation state is due to either higher lattice energy and the ability of oxygen to form multiple bonds to metals Increasing order of oxidizing power in the series is VO2+