Mr.Halavath Ramesh 16-MCH-001 Dept. of Chemistry Loyola College University of Madras-Chennai

Properties of Transition Elements: 1.have large charge / radius ratio. 2. Are hard and have high densities. 3. Have high melting and Boiling point.4. From compounds which are often paramagnetic. 5. Show Variable Oxidation states.6. Form colored ions and compounds.7. Form compounds with profound catalytic activity. 8.Form stable complexes.

In the modern periodic table elements are classified into four types based on electronic configuration 1.S-block elements 2.P-block elements 3.d- block elements 4.f- block elements The elements whose differentiating electrons enter into (n-1)d sub-level are called d-block elements. The d-block elements in which the atoms or ions having incomplete d-orbitals are called transition elements. A typical transition element shall have an incompletely filled d-sub level either in its elementals form or in any of its chemically significant oxidation state. Therefore all d-block elements are not true transition elements e.g. Zn, Cd, and Hg Exceptional Configuration of Some d-block elements: ** The elements with exceptional configuration in 3d series are Cr(24) ……[Ar] 3d5 4s1 Cu(29)……[Ar] 3d10 4s1

Crystal Field Theory (CFT) Crystal Field Theory (CFT) describes the breaking of degeneracy's of electron orbital state usually d or f orbital's due to a static electric field produced by a surrounding charge distribution (anion neighbors).This theory has been used to describe various spectroscopes of transition metal coordination complexes in particular optical spectra (colors). According to the crystal field theory the interaction between a transitions metal and ligands arises from the attraction between the positively charged metal cat ions and the negatively charge on the non-bonding electrons of the ligands. The electron in the d-orbitals and those in the Ligand repel each other due to repulsion between like charges. Thus the d-electrons closer to the ligands will have a higher energy than those further away which results in the d-orbitals splitting in energy.This splitting is affected by the following factors. 1.The Nature of the metal ion. 2. The metal oxide state.A higher oxidation state leads to a larger splitting relative to the spherical field. 3. The arrangement of the ligands around the metal ion. 4.The co ordination number of the metal (i.e., tetrahedral,octahedral). 5. The nature of the ligands surrounding the metal ion. The stronger the effect of the ligands then the greater the difference between the high and low energy d groups.