Transcript Colors & How We Preceive it

Colour and Magnetism
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The relationship between colours and metal complexes
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Colour & How We Perceive it
Artist colour wheel
showing the colours which
are complementary to one
another and the wavelength
range of each colour.
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The colour of visible
light
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Black & White
When a sample absorbs light, what we see is the sum of
the remaining colours that strikes our eyes.
If a sample absorbs all wavelength
of visible light, none reaches our
eyes from that sample.
Consequently, it appears black.
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If the sample absorbs no
visible light, it is white
or colourless.
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Absorption and Reflection
If the sample absorbs
all but orange, the
sample appears orange.
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Further, we also perceive orange
colour when visible light of all colours
except blue strikes our eyes. In a
complementary fashion, if the sample
absorbed only orange, it would appear
blue; blue and orange are said to be
complementary colours.
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Complex Influence on colour
Factors Affecting colour
The metal
Oxidation state
Partially filled d-orbitals (d0 and d10 transparent)
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Light absorption Properties of Metal Complexes
Recording the absorption Spectrum
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The colour of visible light
We have seen that light is a form of energy carried by electric and magnetic fields traveling at 186,000 miles per second. Light has
both particle and wave characteristics. The wavelength of the light deter-mines both its colour and its energy; the shorter the
wavelength, the higher the energy. Light, also called electromagnetic radiation, ranges in wavelength from gamma rays (10 15 m)
through the visible region (500 nm) to the radio wave region (100 m). In the visible region, white light contains a spectrum of
wavelengths from 400 nm (violet) to 780 nm (red); these can be seen in a rainbow or when light passes through a prism. The
colour of substances depends on the colour of light absorbed by the molecules or atoms that compose the substance. This, in turn,
depends on the energy separations between electron orbits. When a molecule or atom absorbs light, electrons are excited from
lower energy orbits to higher energy orbits. If the energy of the light is high enough, light can break chemical bonds and destroy or
change molecules through photode composition; usually, however, the energy is simply given off again as heat or light through
relaxation. The specific wavelengths at which molecules or atoms absorb or emit light serve as fingerprints for specific substances,
making spectroscopy—the interaction of light and matter—a useful tool in identifying unknown substances. Magnetic resonance
imaging and laser devices are two important applications of light and its interaction with matter. Light is a fundamental part of our
lives; by it, we see everything that we see. Sunlight is what keeps the earth alive and is our ultimate energy source. Human eyes
can see a narrow band of light called visible light, but humans use many other wave-lengths for various purposes: X-rays and
gamma rays are used in medicine, infrared light is used in night vision technology, microwaves are used in cooking, and radio
waves are used in communication. The human eye evolved to see not only different intensities of light (black and white vision) but
different colours as well. The colours that we see depend on the interaction of light with the molecules or atoms within the thing we
are looking at.
Just as we can identify some things by their colour in the visible region of the spectrum, so scientists can identify substances by
their “colour” in other parts of the spectrum; this is called spectroscopy. Spectroscopy is used to make measurements important to
society. For example, ozone levels in the upper atmosphere are monitored by spectroscopy, and magnetic resonance imaging (MRI)
is a form of spectroscopy by which doctors image internal organs. The development of technology such as MRI is extremely
beneficial to humans, but it also raises difficult questions—who should benefit from that technology? Does the high cost of
technology leave some people unable to afford it? Is that fair? The ability to make concentrated and pure forms of light with lasers
has also impacted society. From CD players to supermarket scanners to laser guided bombs, lasers have changed the way we live in
the 40 years that have passed since their discovery.
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