Ch 10 - Colour vision and colour theory

Question 1

what is happening w white vs black objects

Answer 1

white - reflecting all visible light

black - absorbing all visible light

Question 2

4 processes that happen when people see colour

Answer 2

1. light source generates light
2. light that is not absorbed by obj either passes through or reflects
3. structures in the retina absorb light
4. electrical signals are transmitted to and interpreted by the brain

Question 3

what does light do to electrons in structures?

Answer 3

causes transitions between quantum states

Question 4

opsins

Answer 4

proteins in the retina (back of the eye) that sense visible light

most humans have 3 diff opsins in ours: long wavelength sensitive (“red”, peak 564. - 580 nm), middle wavelength sensitive (“green” peak 534-555 mm), short wavelength sensitive (“blue”, peak 420-440nm)

each can absorb different wavelengths of light, bc multiple electron transitions possible so difference cone cells excited and we see a range in colours

Question 5

chromophore, aka

Answer 5

aka photopigments

components of chemical structure that absorb or emit light

Question 6

what vitamin are structures of many chromophores based on

Answer 6

vitamin A, retinal

Question 7

what type of colour vision do people have?

Answer 7

trichromatic colour vision

Question 8

how to retinal like structures interact w visible light?

Answer 8

many conjugated bonds and in some conjugated systems quantum states are available that correspond w energy of visible light.

variation in opsin environment of retinol allows to see red, green and blue

Question 9

how do we see colours other than red blue and green

Answer 9

brain uses signals from two or more cones construct our perception of each colour (ex see yellow when red and green cones stimulated)

Question 10

diff between colour wheel/how we perceive light and visible spectrum

Answer 10

visible spectrum shows different colours corresponding to different wavelengths while we see many non spectral colours which are constructed by our brains from lights of different wavelengths (ex magenta a mix of blue and red light, not rep by a specific wavelength on the electromagnetic spectrum)

Question 11

additive colours

Answer 11

colours created by mixing light w different wavelengths

Question 12

RGB Numbers

Answer 12

A way colours are often represented, each red blue and green goes up to 255

Question 13

CMYK systems

Answer 13

printers etc use cyan, magenta, and yellow to create colourse, inks subtract colour from the paper. cyan absorbs red light from paper so appears cyan (blue and green), magenta absorbs green light so seen as magenta( blue and red) yellow absorbs blue so appears combo green and red (yellow)

use subtractive colour mixing

Question 14

colour blindness

Answer 14

ppl may not have genes to produce all 3 opsins, retina could be damaged or there could be damage in areas of the brain responsible interpreting colours

X linked, so more common in men because women have backup (x linked recessive)

Question 15

conjugated systems

Answer 15

alternating multiple and single bonds

p orbital interactions lead to delocalized electrons, shared by more than two atoms in the system. this leads to planarity and single bonds being shorter than normal and double/ triple bonds longer than normal

Question 16

1,3-butadiene

Answer 16

important organic molecule

2 carbon carbon double bonds sep by one c-c single bond, planar

sp2 hybridized carbons so trigonal planar

Question 17

what does sigma bonding help determine as opposed to pi

Answer 17

sigma determines overall shape of the molecule pi bonding more relevent to electronic properties and reactivit of molecule

Question 18

how to determine whether a molecular orbital is bonding or antibonding

Answer 18

look at bonding and antibonding regions, if more bonding regions bonding, more antibonding regions then *, antibonding

Question 19

how to use mo theory to determine bonding etc for a molecule

Answer 19

figure out hybridization scheme - what atomic orbitals are left over???

draw out what different pi orbitals could be formed based on orientation of unhybridized orbital

write out according to energy levels of different orbitals, lowest has least nodes and up based on amount of nodes

how many electrons? fill the orbitals based on regular orbital filling rules

Question 20

why are all atoms in conjugated system on the same plane?

Answer 20

cant spin because this would break the bonds

Question 21

equation for energy of particle in a box

Answer 21

n^2 * h2 / 8m*L^2

Question 22

equation for change in energy between quantum states

Answer 22

(nf^2 - ni^2) * h2 / 8m*L^2

Question 23

how to apply energy equation particle in a box to electrons in MOs finding wavelength of light

Answer 23

1. determine the length of the bond system based on the radius of atoms etc
2. apply the equation, transitions if MO1, n = 1, mo2 n = 2 mo3 n = 3 electron weight etc, use length of the bond system as L
3. use energy calculated and the equation E = hc/wavelength to determine the wavelength (wavelength = hc/E)

Question 24

equation for length of a conjugate system

Answer 24

L= square root of [((nfinal^2 - ninitial^2)h^2wavelength)/8mh*c]

Question 25

how can you calculate length of a conjugate system based on other equations

Answer 25

use change in E = hc/wavelength = equation for change in energy of a conjucate system, rearrange for L

Question 26

molecular vibration

Answer 26

atoms in bond oscillate as if attached to a spring

energy spacing between quantized vibrational states correspond to infrared part of electromagnetic spectrum (extends just past red visible region, slightly longer wavelength of about 1 mm)

Question 27

infrared light

Answer 27

wavelength approx 1 mm extends just past red on visible spectrum

generally detected as heat

comes from molecular vibrational transitions

Question 28

infrared spectroscopy

Answer 28

produces spectra, allows for bond types in chemical compounds to be identified

y axis displays transmission, at a maximum when absorption is minimal

x axis cm^-1, wavenumber, related to frequency and wavelength. Wave number = 1/wavelength

because measures transmission, peaks pointing down (so troughs) rep where molecule absorbing energy

bonds involving hydrogen occur near 3000 cm^-1, C-C, C-O, C-N occur near 2000 cm^-1

Question 29

rotational energy

Answer 29

aka angular kinetic energy: kinetic energy due to the rotation of an object (or electron), part of it’s total kinetic energy

Question 30

rotational states

Answer 30

characterized by angular momentum

can solve the schrodinger equation to find wavefunctions used to describe states of rotating molecule

energy differences between quantized rotational states corresponds to electromagnetic radiation in the microwave region

Question 31

microwave waves and rotational states

Answer 31

energy diff between quantized rotational states corresponds to electromag radiation in microwave region

wavelength around 1 m to 1 cm length

Question 32

how does a microwave work?

Answer 32

microwaves match energy required to transition from ground state to excited rotational states

during relaxation back to ground, heat is emit, heats up everything around

matches rotational energy transitions in water, so food w/ high water content works especially well in microwave

Question 33

quantum dots

Answer 33

materials that glow/emit light at various wavelengths when absorb uv light

super super small so properties governed by quantum mechanics, electrons bound to super small 3D spaces
- size of this space relates to characteristics including colour

nanocrystals (particles smaller than 100 nm in one dimension) and semiconductors (materials more conductive than insulators, not as conductive as conductors)

Question 34

fluorescence

Answer 34

occurs when lower energy light emitted after electron excited to higher energy state

Question 35

synthesis of quantum dots

Answer 35

done using ionic forms of the elements (ex. Ch2+ and S2-)

varying reaction time and temp controls quantum dots’ size, longer rxn time bigger dots

Question 36

is radiation harmful?

Answer 36

only ionizing radiation which has enough energy to cause electrons removed from matter/alter structure of molecules
inc. uv, x rays, gamma rays

non ionizing are ok - inc visible, radio, microwave, infrared

Question 37

summary: what regions of electromagnetic spectrum promote the following

1. ionization
2. electron transitions
3. molecular rotation
4. bond vibration

Answer 37

1. uv, x-rays, gamma rays
2. visible, most of uv
3. microwaves
4. infrared

Question 38

if theres a triple bond in a conjugated system, how many of the bonds are part of the system?

Answer 38

only one of the pi bonds is part of the conjugated system

Question 39

as n increases how does energy spacing change?

Answer 39

as n increases changes in energy increase look at pg 4.24 based on equation e = n^2 - ni^2/jhjhg n on the top, so as ^^^ E increases

Question 40

mo and atoms on same plane

Answer 40

take into account MOs and how an atom may need to twist