CD - Coloured Molecules

Question 1

what is a conjugated system?

Answer 1

alternating double and single bonds

allows overlap of p-orbitals = extends delocalisation

Question 2

why do some things appear white/colourless?

Answer 2

all wavelengths of visable light are reflected (tranmitted if a transparrent liquid)

Question 3

why do some objects appear coloured?

Answer 3

wavelengths corresponding to particular colours are absorbed by substances in the the object and reflects the complimentory colour

Question 4

what is reflected when wavelengths are absorbed by coloured objcts?

Answer 4

the complimentory colour is seen

Question 5

what happens to the e- when an organic molecule absorbes visable light?

Answer 5

they are excited - go from ground state to a higher energy level
∆E=hv change in energy is proportional to frequency absorbed

Question 6

what do colourless compounds absorb?

Answer 6

ultraviolet radiation and reflect all visable light

this is why they apprear colourless

they have a much larger energy gap = less delocalisation

Question 7

what 2 factors can effect colour?

Answer 7

• the more electrons that are delocalised in a conjugated system = smaller energy gap
• smaller energy gap = absorption of longer wavelengths

Question 8

calculations

how do you calculate energy of one mole of photon - youre given wavelenght?

Answer 8

1. rearrange c=wavelenght x v to v=c/wavelength
2. calculate ∆E=hv
3. divide ans by 1000
4. multiply ans by avogadros constant to find one mole

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