Many times students ask the question as to how do we figure out what colour a complex will be. This is a basic starting point and applies to the CAPE Chemistry Syllabus, Module 3 Section 5.

1. Colour And The Spectrochemical Series
WHY SUBSTANCES ARE COLOURED
Spectrochemical series
A t f li d i d f i i li d fi ld
WHITE AND BLACK
A substance appears coloured because it
absorbs light that corresponds to one or
more of the wavelengths in the visible
region of the electromagnetic spectrum
(4000 to 7000 Å) and transmits or reflects
An arrangement of ligands in order of increasing ligand field
strength.
Wavelength of light absorbed by a complex depends on the
energy difference between the two groups of 3d orbitals
A combination of all
wavelengths in the visible
region is called “white
light”; sunlight is an
example. The absence of
In the table below, you can see the relationships among colours absorbed and colours transmitted or reflected in the visible region. The first
l d l h l h b b d h l l h l d h h l h f l h b b d b h
(4000 to 7000 Å) and transmits or reflects
the other wavelengths. which are split by the ligand field. This energy difference
depends on ligand field strength and allows the calculation of
wavelength of light absorbed (using E = hν and ν = c/λ).
p
all wavelengths in the
visible region is blackness.
column displays the wavelengths absorbed. The spectral colour is the colour associated with the wavelengths of light absorbed by the
sample. When certain visible wavelengths are absorbed from incoming “white” light, the light not absorbed remains visible to us as
transmitted or reflected light. For instance, a sample that absorbs orange light appears blue. The complementary colour is the colour
associated with the wavelengths that are not absorbed by the sample. The complementary colour is seen when the spectral colour is
removed from white light.
A colour wheel shows
colours and their
complementary colours.
For example, green is the
complementary colour of
d h d h blred. The data in the table
at left are given for
specific wavelengths.
Broad bands of
wavelengths are shown
Compiled by Denison at Global in Cunupia. 739‐2656.
wavelengths are shown
in this colour wheel.