Inorganic Chemistry Sixth Edition Chapter 8- Physical techniques in inorganic chemistry Modified By Dr. Cheng-Yu Lai PHYSICAL CHEMISTRY: MATTER, AND CHANGE 2E| PETER ATKINS| JULIO DE PAULA | RONALD FRIEDMAN INORGANIC CHEMISTRYQUANTA, 6E| SHRIVER| WELLER| OVERTON | ROURKE | ARMSTRONG ©2014 W. H. H. FREEMAN FREEMAN AND D COMPANY ©2014 W. COMPANY 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).