Download File

TOPIC 13
THE PERIODIC TABLETHE TRANSITION METALS
13.2
COLOURED COMPLEXES
ESSENTIAL IDEA
d-orbitals have the same energy in an isolated
atom, but split into two sub-levels in a complex
ion. The electric field of ligands may cause the
d-orbitals in complex ions to split so that the
energy of an electron transition between them
corresponds to a photon of visible light.
NATURE OF SCIENCE (1.10)
Models and theories – the color of transition metal
complexes can be explained through the use of models and
theories based on how electrons are distributed in dorbitals.
NATURE OF SCIENCE (4.1)
Transdisciplinary-color linked to symmetry can be explored
in the sciences, architecture and the arts.
UNDERSTANDING/KEY IDEA
13.2.A
The d sub-level splits into two sets of
orbitals of different energy in a complex
ion.
Complex Ions (Color) - Iwanowski
UNDERSTANDING/KEY IDEA
13.2.B
Complexes of d-block elements are
colored, as light is absorbed when an
electron is excited between the d-orbitals.
UNDERSTANDING/KEY IDEA
13.2.C
The color absorbed is complementary to
the color observed.
APPLICATION/SKILLS
Be able to explain the effect of the
identity of the metal ion, the
oxidation number of the metal and
the identity of the ligand on the
color of transition metal ion
complexes.
APPLICATION/SKILLS
Be able to explain the effect of
different ligands on the splitting of
the d-orbitals in transition metal
complexes and color observed using
the spectrochemical series.
Ion
e- configuration
color
Sc3+
[Ar]
Colorless
Ti3+
[Ar]3d1
Violet
V3+
[Ar]3d2
Green
Cr3+
[Ar]3d3
Violet
Mn2+
[Ar]3d5
Pink
Fe3+
[Ar]3d5
Yellow
Fe2+
[Ar]3d6
Green
Co2+
[Ar]3d7
Pink
Ni2+
[Ar]3d8
Green
Cu2+
[Ar]3d9
Blue
Zn2+
[Ar]3d10
Colorless
COLORS OF 3d TRANSITION IONS

The color of the complex depends upon:
◦ The nuclear charge and density of the central
ion.
◦ The charge density of the ligand.
◦ The number of d electrons present and hence
the oxidation number of the central ion.
◦ The shape of the complex ion.
Do not confuse the color of the transition
metals in solution with the emission of
color produced when electrons return to
their ground state as in the flame test.
 The transition metals absorb light as the d
orbitals split into two sublevels.

The visible light portion of the EM
spectrum ranges from 400-700nm.
 The color we see depends upon the
wavelength.


The color of a substance is determined by
which color of light it absorbs. It will then
transmit the complementary color.

[Fe(H2O)6]3+ appears yellow because it
absorbs blue light. Yellow is the
complementary color of blue.


www.chemconnections.org
The color wheel can be found in the data
booklet in section 17.
COLOR WHEEL
The d orbitals in an isolated transition
metal all have the same energy and are
said to be degenerate.
 When a ligand approaches a transition
element, the lone pairs of electrons on the
ligand cause the d orbitals of the
transition element to split into 2 sublevels.
 When light passes through the solution,
electrons can be excited to the higher
energy sublevel.

An amount of energy is absorbed
depending upon the frequency of light.
 If a photon of green light is absorbed,
then the complementary color purple will
be transmitted.


The energy separation between the
orbitals depends upon the following:
◦ The nuclear charge and identity of the central
metal ion.
◦ The charge density of the ligand.
◦ The geometry of the complex ion.
◦ The number of d-electrons present, hence the
oxidation number of the central ion.





Ligands interact more effectively with the d
orbitals of ions with higher nuclear charge.
The coordinate bond is stronger with ions of
higher charge.
The higher the charge the more they can
absorb light in the higher energy portion of the
visible light spectrum.
Mn2+ absorbs in the green region (˜490nm)
and Fe3+ absorbs in the blue region (˜450nm).
Remember that shorter wavelengths have
higher frequencies/energy.
NUCLEAR CHARGE AND IDENTITY
OF THE CENTRAL METAL ION
The energy separation of the d-orbitals
depends upon the charge density of the
ligand.
 The lowest charge density repels the delectrons the least, produces small splitting –
absorbs long wavelengths – lower energy
 The highest charge density repels the dorbitals the most, produces large splitting –
absorbs shorter wavelengths – higher energy
 The spectrochemical series is in section 15 of
the data booklet.

CHARGE DENSITY OF LIGAND

The splitting in energy of the d-orbitals
depends on the relative orientation of the
ligand and the d-orbitals.
GEOMETRY OF THE COMPLEX





The strength of the interaction between the
ligand and the central metal ion depends
upon the number of d-electrons which
directly corresponds to the oxidation state
of the metal.
Fe3+ has 5 d-electrons
Fe2+ has 6 d-electrons
Fe3+ absorbs blue and reflects yellow
Fe2+ absorbs violet and reflects green
NUMBER OF d-ELECTRONS AND
OXIDATION STATE OF METAL ION
Citations
International Baccalaureate Organization. Chemistry
Guide, First assessment 2016. Updated 2015.
Brown, Catrin, and Mike Ford. Higher Level
Chemistry. 2nd ed. N.p.: Pearson Baccalaureate,
2014. Print.
Most of the information found in this power point
comes directly from this textbook.
The power point has been made to directly
complement the Higher Level Chemistry textbook by
Catrin and Brown and is used for direct instructional
purposes only.