1. TOPIC 13 THE PERIODIC TABLE- THE TRANSITION METALS 13.2 COLOURED COMPLEXES

2. ESSENTIAL IDEA d-orbitals have the same energy in an isolated atom, but split into two sub-levels in a complex ion. The electric field of ligands may cause the d-orbitals in complex ions to split so that the energy of an electron transition between them corresponds to a photon of visible light. NATURE OF SCIENCE (1.10) Models and theories – the color of transition metal complexes can be explained through the use of models and theories based on how electrons are distributed in d- orbitals. NATURE OF SCIENCE (4.1) Transdisciplinary-color linked to symmetry can be explored in the sciences, architecture and the arts.

3. UNDERSTANDING/KEY IDEA 13.2.A The d sub-level splits into two sets of orbitals of different energy in a complex ion. Complex Ions (Color) - Iwanowski

4. UNDERSTANDING/KEY IDEA 13.2.B Complexes of d-block elements are colored, as light is absorbed when an electron is excited between the d-orbitals.

5. UNDERSTANDING/KEY IDEA 13.2.C The color absorbed is complementary to the color observed.

6. APPLICATION/SKILLS Be able to explain the effect of the identity of the metal ion, the oxidation number of the metal and the identity of the ligand on the color of transition metal ion complexes.

7. APPLICATION/SKILLS Be able to explain the effect of different ligands on the splitting of the d-orbitals in transition metal complexes and color observed using the spectrochemical series.

8. COLORS OF 3d TRANSITION IONS Ione- configurationcolor Sc 3+ [Ar]Colorless Ti 3+ [Ar]3d 1 Violet V 3+ [Ar]3d 2 Green Cr 3+ [Ar]3d 3 Violet Mn 2+ [Ar]3d 5 Pink Fe 3+ [Ar]3d 5 Yellow Fe 2+ [Ar]3d 6 Green Co 2+ [Ar]3d 7 Pink Ni 2+ [Ar]3d 8 Green Cu 2+ [Ar]3d 9 Blue Zn 2+ [Ar]3d 10 Colorless

9. The color of the complex depends upon: ◦The nuclear charge and density of the central ion. ◦The charge density of the ligand. ◦The number of d electrons present and hence the oxidation number of the central ion. ◦The shape of the complex ion. Do not confuse the color of the transition metals in solution with the emission of color produced when electrons return to their ground state as in the flame test. The transition metals absorb light as the d orbitals split into two sublevels.

10. The visible light portion of the EM spectrum ranges from 400-700nm. The color we see depends upon the wavelength.

11. The color of a substance is determined by which color of light it absorbs. It will then transmit the complementary color. [Fe(H 2 O) 6 ] 3+ appears yellow because it absorbs blue light. Yellow is the complementary color of blue.

12. COLOR WHEEL www.chemconnections.org The color wheel can be found in the data booklet in section 17.

13. The d orbitals in an isolated transition metal all have the same energy and are said to be degenerate. When a ligand approaches a transition element, the lone pairs of electrons on the ligand cause the d orbitals of the transition element to split into 2 sub- levels. When light passes through the solution, electrons can be excited to the higher energy sublevel.

14. An amount of energy is absorbed depending upon the frequency of light. If a photon of green light is absorbed, then the complementary color purple will be transmitted.

15. The energy separation between the orbitals depends upon the following: ◦The nuclear charge and identity of the central metal ion. ◦The charge density of the ligand. ◦The geometry of the complex ion. ◦The number of d-electrons present, hence the oxidation number of the central ion.

16. NUCLEAR CHARGE AND IDENTITY OF THE CENTRAL METAL ION Ligands interact more effectively with the d orbitals of ions with higher nuclear charge. The coordinate bond is stronger with ions of higher charge. The higher the charge the more they can absorb light in the higher energy portion of the visible light spectrum. Mn 2+ absorbs in the green region (˜490nm) and Fe 3+ absorbs in the blue region (˜450nm). Remember that shorter wavelengths have higher frequencies/energy.

17. CHARGE DENSITY OF LIGAND The energy separation of the d-orbitals depends upon the charge density of the ligand. The lowest charge density repels the d- electrons the least, produces small splitting – absorbs long wavelengths – lower energy The highest charge density repels the d- orbitals the most, produces large splitting – absorbs shorter wavelengths – higher energy The spectrochemical series is in section 15 of the data booklet.

18. GEOMETRY OF THE COMPLEX The splitting in energy of the d-orbitals depends on the relative orientation of the ligand and the d-orbitals.

19. NUMBER OF d-ELECTRONS AND OXIDATION STATE OF METAL ION The strength of the interaction between the ligand and the central metal ion depends upon the number of d-electrons which directly corresponds to the oxidation state of the metal. Fe 3+ has 5 d-electrons Fe 2+ has 6 d-electrons Fe 3+ absorbs blue and reflects yellow Fe 2+ absorbs violet and reflects green

20. Citations International Baccalaureate Organization. Chemistry Guide, First assessment 2016. Updated 2015. Brown, Catrin, and Mike Ford. Higher Level Chemistry. 2nd ed. N.p.: Pearson Baccalaureate, 2014. Print. Most of the information found in this power point comes directly from this textbook. The power point has been made to directly complement the Higher Level Chemistry textbook by Catrin and Brown and is used for direct instructional purposes only.