NYJC H2 Chem Transition Elements Lecture Notes

1 Nanyang Junior College H2 Chemistry (9729) Lecture Notes 20 An Introduction to the Chemistry of Transition Elements Lecturer: Ms Theresia Line Ishak JC2/2025 Content • General physical and characteristic chemical properties of the first set of transition elements, titanium to copper • Colour of complexes Learning Outcomes Candidates should be able to: (a) explain what is meant by a transition element, in terms of d block elements forming one or more stable ions with partially filled d subshells (b) state the electronic configuration of a first row transition element and its ions (c) explain why atomic radii and first ionisation energies of the transition elements are relatively invariant (d) contrast, qualitatively, the melting point and density of the transition elements with those of calcium as a typical s block element (e) describe the tendency of transition elements to have variable oxidation states (f) predict from a given electronic configuration, the likely oxidation states of a transition element (g) describe and explain the use of Fe 3+/Fe2+, MnO4–/Mn2+ and Cr2O72–/Cr3+ as examples of redox systems (h) predict, using Eo values, the likelihood of redox reactions (i) define the terms ligand and complex as exemplified by the complexes of copper( II) ions with water, ammonia and chloride ions as ligands (including the transition metal complexes found in the Qualitative Analysis Notes) (j) explain qualitatively that ligand exchange may occur, as exemplified by the formation of the complexes in (i), including the colour changes involved, and CO/O2 exchange in haemoglobin (k) describe, using the shape and orientation of the d orbitals, the splitting of degenerate d orbitals into two energy levels in octahedral complexes (l) explain, in terms of d orbital splitting and d -d transition, why transition element complexes are usually coloured [knowledge of the relative order of ligand field strength is not required] (m) explain how some transition elements and/or their compounds can act as catalysts References Peter Cann and Peter Hughes. (2002). Chemistry for Advanced Level (pp. 563-581). John Murray (Publishers) Ltd

2 1. INTRODUCTION Our study focuses on the first row of the transition elements (in Period 4). 1.1 Electronic Configuration • Apply Hund’s Rule, Aufbau’s Rule and Pauli’s Exclusion Principle when filling electrons into the orbitals. (Refer to Atomic Structure Lecture Notes) • The 4s subshell is filled with electrons first before the 3d subshell. Reason: The empty 4s subshell has a lower energy than the 3d subshell. Example: 21Sc: 1s22s22p63s23p63d14s2 22Ti: 1s22s22p63s23p63d24s2 23V: 1s22s22p63s23p63d34s2 • Exception: Cr and Cu 24Cr: [Ar]3d54s1 NOT [Ar]3d44s2 29Cu: [Ar]3d104s1 NOT [Ar]3d94s2 Reason: An exactly half-filled or completely filled d su