Nature of Atoms and Molecules

Understanding the nature of atoms and molecules begins with an understanding of light and other kinds of electromagnetic radiation that make up the electromagnetic spectrum. An... 

During the last sixty years, there have been a number of major scientific revolutions, revolutions that have changed the face of science and allowed for the development of major new commercial opportunities. Four of the most important scientific revolutions are understanding the nature of atoms and molecules, the computer, biotechnology, and advanced engineering materials. 

The Bohr/Pauling era allowed us to understand the nature of atoms and molecules and laid the basis for many Important discoveries. The groundwork for chemistry and physics was being laid. 

For the last decade or so, a new method has been developed to control chemical reactions that it is based on the wave nature of atoms and molecules. The new methodology is called quantum control , or coherent control of chemical reactions, and is based on the coherent excitation of the molecule by a laser. Generally speaking, an ultra-short laser pulse creates a wave packet whose time evolution describes the molecular evolution in the superposition of excited states. Quantum control tries to modify the superposition of such an ensemble of excited states and, therefore, influences the motion of the wave... 

At the end of the nineteenth century, scientists began to realize that the laws of classical physics were incompatible with a number of new experiments that probed the nature of atoms and molecules and their interaction with light. Through the work of a number of scientists over the first three decades of the twentieth century, a new theory—quantum mechanics—was developed that was able to explain the behavior of objects on the atomic and molecular scale. 

Note that the paramagnetic or diamagnetic behavior of atoms is a consequence of the quantization of electron spin and the Pauli exclusion principle, both of which are purely quantum-mechanical phenomena. Thus, the experimental observation of the magnetic behavior of atoms (paramagnetic or diamagnetic) represents further experimental confirmation of the quantum-mechanical nature of atoms and molecules. 

Nature of atoms and molecules, elements and compounds Atoms... 

Topics in the present book on chemistry and life science include studies of atoms and molecules in motion, the development of new processes and materials, nature s secrets of biological growth and form, physical techniques in biology, progress in understanding the human body and mind, and the computer modelling ofthe human heart. 

We have seen that isotope effects on the properties of atoms and molecules are usually small, and this is true for all except the lightest elements. Consequently separation of single isotopes from mixtures of isotopes or isotopomers is tedious and difficult. The difficulty is compounded by the fact that the desired isotope is often present at low or very low concentration in the starting material (normally a naturally occurring fluid, ore, or mineral). Even so, the nuclear properties of certain separated isotopes are enough different from their sisters to justify the (usually enormous) expense of preparing isotopically pure or nearly pure materials. Three important examples follow ... 

As science developed, our accumulation of knowledge about the structure of atoms and molecules was an achievement of early philosophers and scientists. These men and women did not use scientific procedures, but they did build the foundation of our current understanding of the structure of matter and how different species of matter interact. This history has led to our current understanding of the theoretical and practical nature of the chemical elements. 

The little man, or homunculus, as it was sometimes called, was imaginative, of course—the mind sometimes creates such illusions when examining an object too small or fuzzy to be clearly seen. The notion that the microscopic world consisted of familiar objects reduced to a small scale was also incorrect. As scientists probed the nature of particles, they realized that the behavior of small objects does not necessarily mimic larger ones. This discovery opened up new vistas in science as well as technology, including the subject of this chapter—technology on the scale of atoms and molecules. 

The Dirac-Pauli representation is most commonly used in all applications of the Dirac theory to studies on electronic structure of atoms and molecules. Apart of historical reasons, there are several features of this representation which make its choice quite natural. Probably the most important is a well defined symmetry of and in the case of spherically-symmetric potentials V. The Dirac Hamiltonian... 

So we find that the pH of rain depends, in great part, on the concentration of atmospheric C02, which depends on the pH of the oceans. These systems are interconnected with global temperatures, which naturally connect to the countless living systems on Earth. How true it is—all the parts are intricately connected, down to the level of atoms and molecules ... 

It has been one of the great unifying discoveries of natural science that all matter, however complex, is made up of atoms and molecules. The molecules are combinations of atoms, there being about 100 different kinds of atoms in nature. Some molecules are very small and contain only two atoms. Others can be extremely large, such as the molecules of proteins and other components of living matter. 

---