Intermediate Topic 671 of 1102 Inorganic Chemistry
Colored Ions
Partly filled d orbitals allow visible light absorption in compounds.
In-depth explanation of Colored Ions
Transition metal ions are often coloured because they absorb visible light to promote electrons between d orbitals that ligands have split in energy, a d-d transition. The size of this crystal field splitting sets the wavelength absorbed, and the complementary colour is what the eye sees. Ions with empty d orbitals, such as Sc3+ and Ti4+, are colourless because no d-d transition is possible, and so are ions with full d10 shells, such as Zn2+. The colour depends on the metal, its oxidation state and its ligands. For example, Cu2+ is pale blue in water but deep blue in ammonia.
Going deeper: Colored Ions
Key ideas: Color arises from d-d transitions between split d levels in a ligand field, absorbing visible light and showing the complementary color. Delta o determines the wavelength: E = h c over wavelength. Needs partially filled d subshell: Cu2+ (d9) blue, Ni2+ green, Fe3+ yellow-brown, Cu+ (d10), Zn2+ (d10), Sc3+ (d0) colorless. Charge-transfer bands give intense colors such as MnO4- purple and CrO4 2- yellow without d electrons.
Common mistakes and connections: Students say color is the color absorbed; what we see is the complementary color. Ligand change shifts color: Cu(H2O)4 2+ pale blue turns deep blue with NH3. MnO4- is intensely colored although Mn(VII) is d0, because of ligand-to-metal charge transfer. Links to crystal field theory, spectrochemical series and spectroscopy.
Visualization of Colored Ions
Visible spectrum: an ion absorbing one colour appears with the complementary colour, for example Cu2+ absorbs red-orange and looks blue. The interactive lesson shows this as a live animation or chart.
Worked example and use case
Chromium(III) ions in aqueous solution appear violet, while manganese(II) ions are very pale pink.
Frequently asked questions about Colored Ions
What is Colored Ions?
Partly filled d orbitals allow visible light absorption in compounds.
Is Colored Ions a beginner, intermediate or advanced topic?
Colored Ions is a intermediate topic in Inorganic Chemistry. It builds on the vocabulary of beginner topics in this area.
What should I learn before Colored Ions?
Study these earlier topics in Inorganic Chemistry first: Uses of Noble Gases, Transition Metals General, Variable Oxidation States.
What comes after Colored Ions?
The next topics in Inorganic Chemistry are Catalytic Behavior of Transition Metals and Magnetic Properties of Transition Metals.
Can I practise Colored Ions with quizzes?
Yes. The interactive lesson includes a self-check question on Colored Ions, and the Inorganic Chemistry quiz draws on every topic in this area.
Where Colored Ions fits in Inorganic Chemistry
Colored Ions is topic 56 of 113 in Inorganic Chemistry.