Inorganic Chemistry Sixth Edition Chapter 8

Inorganic Chemistry
Sixth Edition
Chapter 8- Physical
techniques in inorganic
chemistry
Modified By Dr. Cheng-Yu Lai
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Diffraction methods
Diffraction techniques, particularly those using X-rays, are the most
important methods available to the inorganic chemist for the
determination of structures.
The method is used to determine the positions of the atoms and
ions that make up a solid compound and hence provides a
description of structures in terms of features such as bond lengths,
bond angles, and the relative positions of ions and molecules in a
unit cell.
Figure 8.1 Bragg’s equation is derived by treating layers of atoms as reflecting
planes. X-rays interfere constructively when the additional path length 2d sin is
equal to an integral multiple of the wavelength .
Diffraction methods
• Powder Diffraction methods
Key point:
Powder X-ray diffraction is used mainly for phase
identification and the determination of lattice
parameters and lattice type. A powdered
(polycrystalline) sample contains an enormous
number of very small crystallites, typically 0.1 to
10 μm in dimension and orientated at random.
• Single-crystal X-ray diffraction
• Neutron diffraction
Key point: The scattering of neutrons by crystals yields diffraction data that give additional
Information on structure, particularly the positions of light atoms.
Absorption spectroscopy
Figure 8.8 The electromagnetic spectrum
with wavelengths and techniques that make
use of the different regions.
Ultraviolet–visible spectroscopy
Key points: The energies and intensities of electronic transitions provide
information on electronic structure and chemical environment; changes in
spectral properties are used to monitor the progress of reactions.
Ultraviolet–visible spectroscopy (UV–visible spectroscopy) is the
observation of the absorption of electromagnetic radiation in the UV and
visible regions of the spectrum. It is sometimes known as electronic
spectroscopy because the energy is used to excite electrons to higher
energy levels.
Schematic representation of a double beam UV-VIS spectrophotometer.
Fluorescence emission spectroscopy
Fluorescence
concern the emitted
electromagnetic
radiation, usually in
the visible or nearinfrared region of
the spectrum, from a
compound that has
been electronically
excited, normally
with UV radiation.
IR and Raman spectroscopy
An IR spectrum can be recorded in terms
of transmittance or absorbance, and
provides information about the energy and
intensity of an absorption.
An IR spectrum can be recorded in
terms of transmittance or absorbance,
and provides information about the
energy and intensity of an absorption.
Ionization-based techniques
In photoelectron spectroscopy, high-energy electromagnetic radiation
(UV for the ejection of valence electrons, X-ray for core electrons) expels
an electron from its orbital, and the kinetic energy of the photoelectron
is equal to the difference between the photon energy and the
ionization energy of the electron.
Mass spectrometry
Key point: Mass spectrometry is a technique for determining
the mass of a molecule and of its fragments.
Chemical analysis
Atomic absorption spectroscopy
Key point: Almost every metallic element can be determined
quantitatively by using the spectral absorption characteristics of atoms.
Thermal analysis
Key points: Thermal methods include thermogravimetric analysis,
differential thermal analysis, and differential scanning calorimetry.
Thermogravimetric analysis is most useful
for desorption, decomposition, dehydration,
and oxidation processes. For example, the
thermogravimetric curve for CuSO4.5H2O
from room temperature to 300.C shows
three stepwise mass losses (Fig. 8.43),
corresponding to the three stages in the
dehydration to form first CuSO4.3H2O, then
CuSO4.H2O, and finally CuSO4.
The thermogravimetric curve obtained for CuSO4.5H2O as the
temperature is raised from 20°C to 500°C. The red line is the mass of
the sample and the green line is its first derivative (the slope of the
red line).