DM.3 Flashcards
Color in transition metal compounds and complexes
What chemical property of transition metals is related to their colours?
partially filled d-orbitals of the metal ions.
What colour does Fe2+ ions give in solution?
Green.
What colour does Fe3+ ions give in solution?
Orange/brown.
What colour does Cu2+ ions give in solution?
Blue.
In terms of absorbance and transmission, when will a substance appear coloured?
When it absorbs or transmits light in the visible region, the substance will appear coloured.
What happens when solutions of sodium hydroxide or ammonia are added to solutions containing transition metal ions?
They will form coloured precipitates of metal hydroxide complexes.
Which metal hydroxide precipitate will redissolve if excess ammonia solution is added?
Cu(OH)2, it will give a deep blue-purple solution. This solutions then contains a copper ammonia complex.
Will either iron(II) or iron(III) hydroxide dissolve in excess ammonia?
No, because they do not form complexes with ammonia.
In terms of energy and electrons, when is light absorbed by an atom?
Light is only absorbed by an atom when the energy of the light matches the energy gap between two energy state in the atom. If it does, an electron will be excited from an orbital will a lower energy to one will a higher energy. By absorbing the light energy, the atom moves from its group state to the excited state.
How can you find out the frequency of the light absorbed?
ΔE = hv where v is the frequency of the light and h is plank’s constant.
What causes splitting of transition metal’s d orbitals?
Ligands surrounding the metal ion.
Why does the splitting of d orbitals result in coloured transition metal complexes?
This is because the difference between the two d orbital ΔE caused by splitting matches the absorption of visible light.
What colour is seen in terms of absorption and transmission?
The colour of the absorption is not seen, the complementary colour, which is reflected or transmitted is seen.
What does the colour of the transition metal complexes depend on?
The types and numbers of ligands that surround the metal ion, which causes characteristic splitting patterns and therefore colour.
What are ligands?
Ligands are negative ions or molecules that can donate a pair of electrons to form a covalent bond with a metal ion. They are similar to nucleophiles in organic chemistry.
