The Mysterious Electron

Scientists have known for a long time that it is incorrect to think of electrons as tiny particles orbiting the nucleus like planets around the sun. Nevertheless, nonscientists have become used to picturing them in this way. In some circumstances, this solar system model of the atom may be useful, but you should know that the electron is much more unusual than that model suggests. The electron is extremely tiny, and modern physics tells us that strange things happen in the realm of the very, very small. 

There are two ways that scientists deal with the problems associated with the complexity and fundamental uncertainty of the modern description of the electron  

Probabilities In order to accommodate the uncertainty of the electro ns position and motion, scientists talk about where the electron probably is within the atom, instead of where it definitely is. 

Through the use of analogies and a discussion of probabilities, this chapter attempts to give you a glimpse of what scientists are learning about the electron s character. 

The waveform shows the variation in the intensity of motion at every position along the string. 

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The concept of chemical periodicity is central to the study of inorganic chemistry. No other generalization rivals the periodic table of the elements in its ability to systematize and rationalize known chemical facts or to predict new ones and suggest fruitful areas for further study. Chemical periodicity and the periodic table now find their natural interpretation in the detailed electronic structure of the atom indeed, they played a major role at the turn of the century in elucidating the mysterious phenomena of radioactivity and the quantum effects which led ultimately to Bohr s theory of the hydrogen atom. Because of this central position it is perhaps not surprising that innumerable articles and books have been written on the subject since the seminal papers by Mendeleev in 1869, and some 700 forms of the periodic table (classified into 146 different types or subtypes) have been proposed. A brief historical survey of these developments is summarized in the Panel opposite. 

As the atomic number increases, so does the positive charge of the nucleus, and the electrons are bound with a higher energy. However, this increase is not linear. For example, the electrons in the d orbital of the third shell have a higher energy than those in the s orbital of the fourth shell, and hence the latter are filled first. The consequence is the unexpected behavior of the first ten transition elements. In the case of the actinides and lanthanides, even more inner orbitals are occupied. Nature is not so simple, but the scheme should help to visualize this complex structure. And if one can assign the electrons of an element, one is a step closer to successfully unraveling the mysteries of the Periodic Table. 

Methods for making both forms solvent-soluble were the subject of many patents and closely guarded industrial secrets, but much of the mystery was cleared up in two papers by Gerstner [23] and Smith and Easton [24] published in 1966, by which time X-ray diffraction, electron microscopy and disc centrifuge particle sizing methods had been brought to bear on the problem. 

However, the secret of transmutation did not lie in chemistry and the peripheral electrons that determine the chemical properties of the atom. Instead, the solution to this mystery had to be sought in the nucleus of the atom and the strong and weak nuclear interactions which organise and stracture it. 

Yet, in the end, the hound proved mortal, not supernatural its unearthly flickering flame the result of a cunning preparation of phosphorus. (For other cunning preparations of phosphorus, see the discussion of phosphinidenes in Chapter 11 in this volume.) We too have peeled back much of the mystery and cleared away most of the fog that once surrounded the strucmres, electronic... 

The key that unlocked the mystery of the line spectra was found with the simplest atom, hydrogen. It consists of a nnclens composed of a single positive charge and a single electron. Bohr made the assumption that since atoms are observed to be stable, recombination of an election and a proton can only lead to certain discrete states 24). The energy of these states was calcnlated to be... 

Finally, some authors [71-75] proposed an interpretation of the Aharonov-Bohm effect based on the interaction between the electrons of the beam and electrons of the solenoid. The Aharonov-Bohm effect looses its mystery if we acknowledge that Newton s third principle is transgressed here. Indeed, if electrons within the solenoid cannot act on electron of the beams, electron beams can act on the electrons of the solenoid, by means of the momentum equations [70]... 

Bohr s planetary atomic model proved to be a tremendous success. By utilizing Planck s quantum hypothesis, Bohr s model solved the mystery of atomic spectra. Despite its successes, though, Bohr s model was limited because it did not explain why energy levels in an atom are quantized. Bohr himself was quick to point out that his model was to be interpreted only as a crude beginning, and the picture of electrons whirling about the nucleus like planets about the sun was not to be taken literally (a warning to which popularizers of science paid no heed). 

In a series of papers between 1956 and 1965, Marcus solved much of the mystery by outlining a description of the probability of fluctuations in the geometry of reactants and their solvents. These fluctuations lead to changes in the energy barriers that the reactants must surmount before an electron can be transferred from one molecule to another. Marcus extended the theory to other systems, such as electrochemical rate constants at electrodes, and to chemiluminescent electron transfer reactions. The by-now famous inverted effect is a consequence of his theory after a certain point, adding more energy to an electron transfer reaction actually slows the process. Scientists believe photosynthesis can occur because of the inverted effect. 

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