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CHEM 121 Studioby Learn4Less · UBC CHEM 121

CHEM 121 glossary

Complementary colour

The colour opposite a given colour on the colour wheel. A substance that absorbs one band of visible light looks like the complement of the light it absorbs, because that is what remains of the white light it transmits or reflects.

Colour wheel: absorbs blue light (450 nm) → looks yellowComplementary colours sit opposite each other: violet (400–435 nm) opposite yellow-green (560–580 nm); blue (435–480 nm) opposite yellow (580–595 nm); green-blue (480–490 nm) opposite orange (595–650 nm); blue-green (490–500 nm) opposite red (650–750 nm); green (500–560 nm) opposite purple (non-spectral).violet light, 400–435 nmblue light, 435–480 nmgreen-blue light, 480–490 nmblue-green light, 490–500 nmgreen light, 500–560 nmyellow-green light, 560–580 nmyellow light, 580–595 nmorange light, 595–650 nmred light, 650–750 nmpurple is not a single wavelength (red + violet light mixed); it is seen when green light is absorbedviolet400–435 nmblue435–480 nm▲ ABSORBEDgreen-blue480–490 nmblue-green490–500 nmgreen500–560 nmyellow-green560–580 nmyellow580–595 nm◆ OBSERVEDorange595–650 nmred650–750 nmpurplenon-spectralopposite colours are complementary

Absorbed: blue light, 450 nm (band 435–480 nm)

Observed: yellow (580–595 nm on the wheel), the complement opposite

Absorbing blue light (≈ 450 nm) makes a substance look yellow.

Example

A solution that absorbs orange light (595–650 nm) looks green-blue; one that absorbs violet light (400–435 nm) looks yellow-green. Leaves absorb blue and red light, so the green in between is what we see.

See alsoVisible lightλmax (wavelength of maximum absorption)Chromophore