Atoms modern view

Another piece of information was necessary before one arrives at a periodic table which is close to the modern view. This is the whole number rule which states that the masses of atoms on the 160 scale (i.e. mass of the major isotope of oxygen is 16.00) tend to have close to integer values. This information was provided by W. D. Harkins (vide infra) and F. W. Aston (Historical Vignette 1.2). 

The modern view of HX addition is that H+ is transferred from HX to the alkene to give a carbocation. The major product is the one derived from the more stable carbocation. Compare the energies of 1-propyl and 2-propyl cations (protonated propene), 2-methyl-1-propyl and 2-methyl-2-propyl cations (protonated 2-methylpropene), and 2-methyl-2-butyl and 3-methyl-2-butyl cations (protonated 2-methyl-2-butene). Identify the more stable cation in each pair. Is the product derived from this cation the same product predicted by Markovnikov s rule Is the more stable carbocation also the one for which the positive charge is more delocalized Compare atomic charges and electrostatic potential maps for one or more pairs of carbocations. 

The Rutherford Experiment movie (eChapter 2.4) shows alpha particles impinging on a thin gold foil. Describe what happens to the alpha particles and discuss how the results of this experiment shaped the modern view of atomic structure. 

The anomeric effect in terms of a stabilizing effect can be illustrated by the concept of "double-bond - no-bond resonance" (14, 15) shown by the resonance structures 4 and 2 or by the equivalent modern view (16, 17) that this electronic delocalization is due to the overlap of an electron pair orbital of an oxygen atom with the antibonding orbital of a C —OR sigma bond (12). 

Atom The smallest portion of an element that can enter into chemical change, and cannot be further subdivided without destroying its identity. The modern view of an atom is of a positively charged nucleus (made up of electrically neutral neutrons and positive protons) surrounded by a cloud of negatively charged electrons. 

Without laving too much stress upon the most modern view, that of regarding electricity atomically by moans of the idea of electrons, all known phenomena justify us in dealing with positive and negative electrical quantities as with chemically active masses, and applying to them the principles of reaction kinetics. 

This illustration shows the modern view of an atom. Notice that a fuzzy, cloud-like region surrounds the atomic nucleus. Electrons move rapidly throughout this region, which represents most of the atom s volume. 

The modern view of the periodic table explains its structure in terms of an Aufbau procedure based on the wave-mechanical model of the hydrogen atom. Although seductive at first glance, the model is totally inadequate to account for details of the observed electronic configurations of atoms, and makes no distinction between isotopes of the same element. The attractive part of the wave-mechanical model is that it predicts a periodic sequence of electronic configurations readily specified as a function of atomic number. The periodicity follows from the progressive increase of four quantum numbers n, l, mi and s, such that... 

Explain the Impact of de Broglie s wave-particle duality and the Heisenberg uncertainty principle on the modern view of electrons in atoms. 

While the Epicurean model appeals to us as being closer to the modern view of atoms and is sometimes pointed to as the origin of atomic theory, in historical terms, it had little effect on the development of natural philosophy. The reason for this was twofold. First, the Epicureans were known less for their physical theories than for their ideas about social and personal behavior, favoring the pursuit of pleasure. Our modern use of the term epicure for someone who enjoys good food and drink reflects this. The second reason that... 

The situation is much the same in liquids, although the molecules are more closely spaced and the molecular interactions are stronger and more frequent. Similarly, in a solid, conduction may be attributed to atomic activity in the form of lattice vibrations. The modern view is to ascribe the energy transfer to lattice waves induced by atomic motions. In a non-conductor, the energy transfer is exclusively via these waves, in a conductor it is also due to the translational motion of the free electrons. 

In the early days of atomic theory, it was often assumed that only an empirical understanding could be achieved beyond the first few rows of the periodic table, where the simple formulation of the aufbau principle breaks down. The modern view is that shell and subshell filling can be accounted for within the central field approximation, provided the centrifugal barrier effects are included. 

Modem views of atomic structure are, as we have seen, based largely on the applications of wave mechanics to atomic systems. Modern views of molecular structure are based on applying wave mechanics to molecules such studies provide answers as to how and why atoms combine. The Schrodinger equation can be written to describe the behaviour of electrons in molecules, but it can be solved only approximately. Two such methods are the valence bond approach, developed by Heitler and Pauling, and the molecular orbital approach associated with Hund and MuUiken ... 

In his theories Lavoisier had been anticipated by a Russian chemist, Mikhail Vasilievich Lomonosov (1711-65) who, in 1756, nearly twenty years before Lavoisier s work on combustion, had rejected the phlogiston theory and had suggested that objects combined with a portion of the air on burning. Unfortunately, he published in Russian, and the chemists of western Europe, including Lavoisier, were unaware of his work. Lomonosov also had startlingly modern views on atoms and on heat, which were fifty to a hundred years ahead of his time. He was a most remarkable man who suffered under the misfortune of having been born in eastern Europe at a time when scientific advance was concentrated in western Europe. 

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