DM bijkm: Complexes & associated colour Flashcards
Explain in simple terms what causes colour.
- When light hits a substance, it may be transmitted, reflected or absorbed
- If frequency absorbed is in visible region, substance is coloured
Explain why specific elements absorb specific frequencies of light.
- When light hits an atom, photons are absorbed
- Electrons promoted to higher energy levels
- Energy of a photon corresponds to gap between energy levels
- Frequency of photon, ν, related to ΔE by ΔE = hν
- Each element has unique energy levels, so absorbs unique frequencies of light
- State what is meant by “complementary colours”.
- List them.
Opposite frequencies of visible light on the colour wheel which, when combined, produce white light.
![](https://s3.amazonaws.com/brainscape-prod/system/cm/331/319/005/a_image_thumb.png?1608116202)
- Give the formulae of the common ions of iron
- Give their colours in aqueous solution
Fe2+, green
Fe3+, orange-brown
- Give the formulae of the common ions of copper
- Give their electronic configuration with respect to Ar
- Give their colours in aqueous solution
![](https://s3.amazonaws.com/brainscape-prod/system/cm/331/319/007/q_image_thumb.png?1611489820)
Cu [Ar] 3d104s1
Cu+, [Ar] 3d10, unstable in solution
Cu2+, [Ar] 3d9, blue
Copper(I) ions are unstable in aqueous solution. Write an equation, showing state symbols, to suggest what they break down to.
2Cu+(aq) → Cu(s) + Cu2+(aq)
What are ligands?
Molecules/anions which surround, and donate a lone pair of electrons to, a metal cation by coordinate (dative) bonding.
The inorganic chem equivalent of nucleophiles
Define the following:
- Monodentate ligand
- Bidentate ligand
- Polydentate ligand
- Monodentate ligand: form one coordinate bond with central metal ion
- Bidentate ligand: form two coordinate bonds with central metal ion
- Polydentate ligand: form several coordinate bonds with central metal ion
Give the corresponding prefix/suffix for naming the complex of each of the following monodentate ligands:
- H2O:
- :OH-
- :CN-
- :NH3
- Halides, :Cl-, :Br-, :I-
- CH3COO:
- H2O aqua
- OH- hydroxy
- CN- cyano
- NH3 amino
- Cl- chloro, Br- bromo, I- iodo
- CH3COO ethanoate
Explain why some transition metal solutions are coloured.
- Ligands form dative bonds with central metal ion, which splits its d-orbitals
- Creates energy gap of right magnitude to allow absorption of visible light
- Electrons are excited to higher energy level
- Frequency absorbed is related to energy gap by ∆E = hv
- Colour seen is complementary colour to that absorbed (due to missing frequency)
Energies of all 5 d-orbitals in transition metals are normally equal.
Further explanation of splitting (not on spec): d-orbitals close to ligand are repelled + pushed to higher energy levels. Those further from ligand are attracted + pushed to lower energy levels
On which factors does the colour of a transition metal complex depend?
- Ligand
- Ligand arrangement (affects splitting)
- Transition metal element
- Oxidation state (number of d-electrons)
Explain why the following are not coloured:
- Titanium(IV) oxide
- Compounds of Sc3+
- Compounds of Zn2+
- Compounds of Cu+
![](https://s3.amazonaws.com/brainscape-prod/system/cm/332/538/201/q_image_thumb.png?1611490720)
They have the following electronic arrangements:
- Ti4+ [Ar]
- Sc3+ [Ar]
- Zn2+ [Ar] 3d10
- Cu+ [Ar] 3d10
No incompletely filled 3d orbitals / all are either empty or full
Dative covalent bonding with ligands cannot occur
3d electron transitions / splitting not possible
What is a complex?
Central transition metal atom or ion surrounded by + bonded coordinately to several ligands.
How would you predict the charge of a complex?
Overall charge of metal atom/ion + ligands.
Charge delocalised over whole ion.
Define “coordination number”.
The number of dative bonds in a complex between the metal atom/ion and ligands.
D__oesn’t necessarily indicate the number of ligands.