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Search for:. John Dalton and Atomic Theory. While all atoms of an element were identical, different elements had atoms of differing size and mass. Dalton also postulated that chemical reactions resulted in the rearrangement of the reacting atoms. Long-term, environmentally acceptable solutions to pollution problems are not attainable without chemical knowledge.
Progress in chemistry can no longer be measured only in terms of economics and utility. The discovery and manufacture of new chemical goods must continue to be economically feasible but must be environmentally acceptable as well.
History of Dalton’s Atomic Theory
The impact of new substances on the environment can now be assessed before large-scale production begins, and environmental compatibility has become a valued property of new materials. For example, compounds consisting of carbon fully bonded to chlorine and fluorine, called chlorofluorocarbons or Freons , were believed to be ideal for their intended use when they were first discovered.
They are nontoxic, nonflammable gases and volatile liquids that are very stable.
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These properties led to their widespread use as solvents, refrigerants, and propellants in aerosol containers. Time has shown, however, that these compounds decompose in the upper regions of the atmosphere and that the decomposition products act to destroy stratospheric ozone. Limits have now been placed on the use of chlorofluorocarbons, but it is impossible to recover the amounts already dispersed into the atmosphere.
The chlorofluorocarbon problem illustrates how difficult it is to anticipate the overall impact that new materials can have on the environment. Chemists are working to develop methods of assessment , and prevailing chemical theory provides the working tools.
New Theories for Chemistry | ScienceDirect
Once a substance has been identified as hazardous to the existing ecological balance, it is the responsibility of chemists to locate that substance and neutralize it, limiting the damage it can do or removing it from the environment entirely. The last years of the 20th century will see many new, exciting discoveries in the processes and products of chemistry.
Inevitably, the harmful effects of some substances will outweigh their benefits, and their use will have to be limited. Yet, the positive impact of chemistry on society as a whole seems beyond doubt. Chemistry has justly been called the central science.
1.2: Atomic Realities and Scientific Theories
Theoretical chemistry unites principles and concepts common to all branches of chemistry. Within the framework of theoretical chemistry, there is a systematization of chemical laws, principles and rules, their refinement and detailing, the construction of a hierarchy. The central place in theoretical chemistry is occupied by the doctrine of the interconnection of the structure and properties of molecular systems.
It uses mathematical and physical methods to explain the structures and dynamics of chemical systems and to correlate, understand, and predict their thermodynamic and kinetic properties. In the most general sense, it is explanation of chemical phenomena by methods of theoretical physics. In contrast to theoretical physics, in connection with the high complexity of chemical systems, theoretical chemistry, in addition to approximate mathematical methods, often uses semi-empirical and empirical methods.
In recent years, it has consisted primarily of quantum chemistry , i. Other major components include molecular dynamics , statistical thermodynamics and theories of electrolyte solutions , reaction networks , polymerization , catalysis , molecular magnetism and spectroscopy. Modern theoretical chemistry may be roughly divided into the study of chemical structure and the study of chemical dynamics.
The former includes studies of: electronic structure, potential energy surfaces, and force fields; vibrational-rotational motion; equilibrium properties of condensed-phase systems and macro-molecules. Chemical dynamics includes: bimolecular kinetics and the collision theory of reactions and energy transfer; unimolecular rate theory and metastable states; condensed-phase and macromolecular aspects of dynamics.