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.
How are ligands attached to the metal ion?
They form a dative covalent bond with the metal ion using a lone pair of electrons.
What are dative bonds also known as?
Coordinate bonds.
Why can’t s block metal ions (group 1 and 2) form complexes with ligands?
Because they cannot accept dative bonds, it would be too many electrons for them. Water will form ion dipole interaction with them.
What are some examples of things that can act as ligands?
H2O OH- NH3 CN- CH3COO- (ethanoate) Halides (Cl-,Br-,I-) H2NCH2CH2NH2 (1,2-diaminoethane)
What is a ligand called when it can form only one dative bond to the metal ion?
Monodentate ligand.
What is a ligand called when it can form two dative bonds to the metal ion?
Bidentate ligand.
What colour is vanadium in the +5 oxidation state?
Yellow
What colour is vanadium in the +4 oxidation state?
Blue
What colour is vanadium in the +3 oxidation state?
Green
What colour is vanadium in the +2 oxidation state?
Purple
What are the four things that effect the splitting of the d-obrbital and therefore the colour?
- The metal ion
- The oxidation state of the metal
- The number and type of ligand involve
- The shape of the complex
What is a technique used to find the concentration of a coloured solution?
Colorimetry.
How should you choose a filter for colourimetry?
You should choose a colour that corresponds to the colour of light that is most strongly absorbed by the solution.
What is the relationship between absorbance and the concentration of a coloured solution?
A = kc, where A is absorbance and c is concentration. They are directly proportional, and k is a constant. This means as the concentration of the coloured solution increases, its absorbance will increase.
