Physics, atomic, early experiments

Atoms consist of electrons and protons in equal numbers and, in all cases except the hydrogen atom, some number of neutrons. Electrons and protons have equal but opposite charges, but greatly different masses. The mass of a proton is 1.67 X 10 24 grams. In atoms that have many electrons, the electrons are not all held with the same energy later we will discuss the shell stmcture of electrons in atoms. At this point, we see that the early experiments in atomic physics have provided a general view of the structures of atoms. 

Warren, W. S. (2000). The Physical Basis of Chemistry, 2nd ed. Academic Press, San Diego, CA. Chapter 5 presents the results of some early experiments in atomic physics. 

In the last 200 years, vast amounts of data have been accumulated to support atomic theory. When atoms were originally suggested by the early Greeks, no physical evidence existed to support their ideas. Early chemists did a variety of experiments, which culminated in Dalton s model of the atom. Because of the limitations of Dalton s model, modifications were proposed first by Thomson and then by Rutherford, which eventually led to our modern concept of the nuclear atom. These early models of the atom work reasonably well—in fact, we continue to use them to visualize a variety of chemical concepts. There remain questions that these models cannot answer, including an explanation of how atomic structure relates to the periodic table. In this chapter, we will present our modern model of the atom we will see how it varies from and improves upon the earlier atomic models. 

X-ray absorption and emission spectroscopy is a field with a distinguished history. At the beginning, i.e., from 1913 to the early thirties, these spectroscopies were dedicated to a systematic exploration of the atomic structure in the context of the periodic system of the elements. The intense work of numerous spectroscopists, which contributed prominently to the foundations of modern atomic physics and to the development of quantum theory, was reviewed in the classical books Spektroskopie der Rontgenstrahlen by M. Siegbahn (1913) and X-Rays in Theory and Experiment by Compton and Allison (1935). 

Figure 26 shows the equations of state, eq. (37), of the actinide metals, calculated by Skriver and co-workers (Skriver et al. 1978, 1980, Brooks et al. 1984), for the fee structure and fig. 27 shows the calculated atomic radii, evaluated from eq. (37). The agreement between theory and experiment implies that the approximations to density functional theory outlined in sect. 3.1 contain the essential physics. Early in the series, Fr-Th, we observe a decrease in radius, which is caused by an increase in the amount of d character (fig. 24). For Th-Pu the calculated atomic radius continues to decrease, but now the cause can be traced to the increasing occupation of the 5f orbitals, which,... 

The development of fast ion beam laser spectroscopy techniques (for short FIBLAS) is not so unusual a case of simultaneous but independent technical evolution both in atomic and molecular physics. Although the concepts involved in both cases were quite similar, the apparatus used in the pioneering experiments were widely different, ranging from the table top mass spectrometer for the early molecular physics work to the largest tandem Van de Graaff accelerators for some of the atomic physics experiments. ... 

Until the advent of modem physical methods for surface studies and computer control of experiments, our knowledge of electrode processes was derived mostly from electrochemical measurements (Chapter 12). By clever use of these measurements, together with electrocapillary studies, it was possible to derive considerable information on processes in the inner Helmholtz plane. Other important tools were the use of radioactive isotopes to study adsorption processes and the derivation of mechanisms for hydrogen evolution from isotope separation factors. Early on, extensive use was made of optical microscopy and X-ray diffraction (XRD) in the study of electrocrystallization of metals. In the past 30 years enormous progress has been made in the development and application of new physical methods for study of electrode processes at the molecular and atomic level. 

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