Colour By Design Flashcards
Why does an object appear white?
Because all the wavelengths of visible light are reflected and are not absorbed so appear white
What happens to light that hits a transparent object?
All the wavelengths of light pass through it
What happens to light that hits a coloured object?
Some wavelengths of the light are absorbed by the object and some of the light is reflected. The colour of the light that is reflected is what colour the object appears to be.
What happens to light hitting a blue object?
Only blue light is reflected. All other colours of light have been absorbed.
The colour of ______ light that has been ______ causes the object to appear the _______ colour of the light that has been absorbed
Visible
Absorbed
Complimentary
Do atoms only absorb photons of visible light to excite electrons from the ground state?
No they can absorb any frequency of light
What colour does an object that absorbs photons of ultraviolet light appear?
It appears colourless
What is a conjugated system?
The electrons in the π bond which are part of a covalent double bond are spread out over the whole molecular system.
What is are 2 examples of a conjugated system?
Benzene, R-COO-
In a conjugated system, what are the electrons said to be?
Delocalised
How does a conjugated system affect the colour of light that the substance absorbs?
The difference between the energy of the ground state and excited state is smaller.
The more delocalised electrons the smaller the energy gap
What happens if the energy gap of the ground state and excited state is smaller?
Longer wavelengths of light are absorbed
What is a useful rule of thumb about the wavelengths of light for a delocalised system of electrons?
A delocalised system with 5 π-bonds in a conjugated system are likely to absorb visible light and be coloured
What is an Arene?
It is a ring shape that is stabilised by electron delocalisation
What is the structure of a benzene?
- Regular planar hexagon
- Bond angles are 120º
- All the carbon-carbon bonds are the same length. (smaller than a normal carbon-carbon bond but larger than a carbon-carbon double bond)
What is the delocalisation of a benzene ring?
It forms two doughnut shapes above and below the plane of the benzene ring molecule. The p-shell forms a figure of 8 where the top is above the plane and the bottom is below the plane. This then morphs into the doughnut shape
In a benzene ring, how are the electrons from a carbon distributed?
3 electrons form σ-bonds between the two carbons either side and the hydrogen.
The 4th electrons forms the π-bond
The more delocalised a structure has….
…..The more stable it is (generally)
How stable is benzene?
It is very stable
What is the name of the old (wrong) model for benzene? What did it look like?
Kekulé’s model
It had alternating double and single bonds
What disproved Kekulés model?
The energy released in the hydrogenation kekulés model was 3x that of a 6 carbon ring with 1 double bond. But the enthalpy change of the hydrogenation of benzene was not 3x and was in fact much smaller than kekulés model
How does benzene react with hydrogen and what is produced?
It only reacts under SPECIAL conditions (300º 30 atm)
C6H12 is produced
What is the shape of kekulés molecule?
It is not a hexagon but is instead a 6 sided shape with alternating smaller sides where the double bonds are and longer sides where the single bonds are.