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)
Degenerate
All 5 d orbitals in the d subshell have the same energy when NOT interacting with anything aka have not formed any dative bonds because no ligands donated electron pair
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
What does the actual SIZE of the gap between the energy levels of the different d orbitals depend on? (After splitting)
The type of ligand attached when forming dative bonds to transition metal ion
Because this determines the amount of interaction with the d orbital, so if the low energy d orbitals are even lower (because even less interaction) and if high energy d orbitals are even high (more interaction)
Why does splitting of the d subshell into different energy level d orbitals depend on?
Some d orbitals lie off axis and interact LESS with ligands so are at lower energy levels
Some d orbitals lie on axis and interact MORE with ligand so at higher energy levels
Structure of answer to explain why different complexes see different colours
Different complexes have different ligands/metal ions/different oxidation stages of metal ion/different coord numbers
So different energy gaps between the split d orbitals
So different complexes absorb different wavelengths of light
And reflect different wavelengths
So we see different colours due to different complexes
How does coordination number affect the colour of complex?
Different shape complexes have different types of splitting
Varies sizes of energy gap 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
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 zinc 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
