5.3 Module 3: Transition Elements


This module extends the study of periodicity encountered within unit F321: Atoms, Bonds and Groups.

By studying the transition elements, this module provides candidates with a deeper knowledge and understanding of inorganic chemistry and the Periodic Table. The module also links with many other areas of chemistry and provides many opportunities to consider chemistry synoptically.

Practical Skills are assessed using specified OCR set tasks.

The practical work outlined below may be carried out as part of skill development. Centres are not required to carry out all of these experiments:

  • * Precipitation of transition metal hydroxides (test-tube scale).
  • * Ligand substitution reaction of complex ions (test-tube scale).
  • * Redox titrations:

the estimation of iron in iron tablets titration with MnO4 - in acid conditions;

the estimation of copper in alloys such as brass by titration using I2/S2O3 2.

5.3.1 Transition Elements

Links AS Unit F321: Atoms, Bonds and Groups

5.3.1 Transition Elements

Context and exemplification - Assessable learning outcomes Properties

* Candidates should use sub-shell notation, eg for Fe: 1s22s22p63s23p63d64s2.

* No detail of how colour arises is required.

* No detail of catalytic processes required.

Candidates should be able to:

(a) deduce the electron configurations of atoms and ions of the d-block elements of Period 4 (Sc-Zn) , given the atomic number and charge;

(b) describe the elements T to Cu as transition elements, ie d-block elements that have an ion with an incomplete d sub-shell;

(c) illustrate:

Precipitation reactions

(d) describe, including ionic equations, the simple precipitation reactions and the accompanying colour changes of Cu2+(aq), Co2+(aq), Fe2+(aq) and Fe3+(aq) with aqueous sodium hydroxide;

Ligands and complex Ions

* Examples should use H2O, Cl-, NH3 as simple monodentate ligands. In examinations, other ligands might be introduced.

(e) explain the term ligand in terms of coordinate bonding;

(f) state and use the terms complex ion and coordination number;

(g) state and give examples of complexes with sixfold coordination with an octahedral shape;

(h) explain and use the term bidentate ligand (eg NH2CH2CH2NH2, 'en');

(i) describe the types of stereoisomerism shown by complexes, including those associated with bidentate and multidentate ligands:

(j) describe the use of cis-platin as an anticancer drug and its action by binding to DNA in cancer cells, preventing division;

Ligand substitution

(k) describe the process of ligand substitution and the accompanying colour changes in the formation of:

(l) explain the biochemical importance of iron in haemoglobin, including ligand substitution involving O2 and CO;

(m) state that the stability constant, Kstab,, of a complex ion is the equilibrium constant for the formation of the complex ion in a solvent from its constituent ions;

(n) deduce expressions for the stability constant, Kstab, of a ligand substitution, eg M2+(aq) + 6X-(aq) . MX6 4-(aq) Kstab = [MX6 4-(aq)]/[M2+(aq)][X-(aq)]6 (see also 5.1.2.b);

(o) relate ligand substitution reactions of complexes to stability constants and understand that a large Kstab results in formation of a stable complex ion;

Redox reactions and titrations

* Non-structured titration calculations could be examined in the context of both acid-base and redox titrations.

(p) describe, using suitable examples, redox behaviour in transition elements;

(q) carry out redox titrations, and carry out structured calculations, involving MnO4 - and I2/S2O3 2.;

(r) perform non-structured titration calculations, based on experimental results.