Colour Of Compounds Flashcards
How many d orbitals make up the d subshell?
5 d orbitals
Energy of all 5d orbitals when not interacting
The same (degenerate)
What happens when light is absorbed by a complex?
When light is absorbed, the electrons (in dative bond) in lower energy d orbitals are promoted to higher energy d orbitals
Size of energy gap between these levels determines frequency of light absorbed
WE SEE LIGHT THAT IS NOT ABSORBED
Do we see the light that is absorbed or not?
We see the LIGHT THAT IS NOT ABSORBED
WE SEE THE LIGHT THAT IS REFLECTED/TRANSMITTED in the visible light spectrum
How does coordination number affect the colour of complex?
Different shape complexes have different types of splitting
Varies sizes of energy gap split between the d orbitals and maybe causes multiple energy gaps
So absorbs different wavelengths of light to excite the electron to high energy levels, transmit different wavelengths and so see different colours
How does oxidation state of transition metal ion affect the colour of the complex?
Different complexes have different oxidation states of metal ion
So varies number of electrons available in the d subshell
Varies the number of electrons that could be promoted from lower d orbitals to higher d orbitals - alters energy split
so different complexes absorb different wavelengths of light: transmit different wavelengths of light to see different colours
3 factors that affect colour of complex
Type of ligand
Coordination number/shape of complex
Oxidation state of the complex
Why are aqueous ions/ complex ions of non transition metals colourless?
Visible light can only be absorbed when energy is used to promote electron over energy gap in d subshell caused by splitting (the right energy gap)
These don’t have electron transitions that can absorb wavelengths of visible light eg because the d orbital is empty or full
Why are Zn 2+ and Cu+ solutions colourless?
Because the d subshell is full so no light can be absorbed to promote electrons over energy gap in the d subshell from a lower energy d orbital to a higher energy d orbital
So no wavelengths of light are transmitted = no colour seen
How does exchange of ligand cause a colour change?
Alters energy split between d orbitals because different ligands will interact with transition metal more than others
Changes portion of visible light absorbed by visible light to promote electrons so changes portion of visible light reflected = colour change
Is it possible to change the oxidation state of a transition metal ion without changing the complex/ligands/coord number?
Yes
Why is Sc 3+ colourless?
Has no electrons in d orbital so no energy is used to promote electrons in d orbital, no splitting occurs
No energy transfer equal to visible light
Method of Spectrophotometry
*Add an appropriate ligand to intensify colour
*Make up solutions of known concentration
*Measure absorption or transmission
*Plot graph of results or calibration curve
*Measure absorption of unknown and compare
What is Spectrophotometry?
determining concentration of solution of complex based on colour
Because absorbance thus colour is proportional to concentration of metal compound in solution
V 5+ oxidation state colour
Yellow
V 4+ oxidation state colour
Blue
V 3+ oxidation state colour
Green
V 2+ oxidation state colour
Purple
