Core of the atom

As in the preceding transition-metal groups, the refractory behaviour and the relative stabilities of the different oxidation states can be explained by the role of the (n — l)d electrons. Compared to vanadium, chromium has a lower mp, bp and enthalpy of atomization which implies that the 3d electrons are now just beginning to enter the inert electron core of the atom, and so are less readily delocalized by the formation of metal bonds. This is reflected too in the fact that the most stable oxidation state has dropped to +3, while chromium(VI) is strongly oxidizing ... 

FIGURE 14.6 (a)Thep-orbitals of Period 3 and heavier elements are held apart by the cores of the atoms (shown in gray) and have very little overlap with each other, (b) In contrast, the atoms of elements in Period 1 are small consequently their p-orbitals can overlap effectiveh with each other and with those of elements in later periods. 

Nucleus The dense central core of the atom in which most of the mass and all of the positive charge is concentrated. The charge on the nucleus distinguishes one element from another. 

The electrons involved are in the core of the atom and should be much less affected by external influences such as chemical bonding which greatly modify the properties of the outer electrons. For light elements however the K and L electrons may also be the valency electrons and significant effects may be observed. 

Replacing ab initio densities with promolecular densities using the ASA expansion may seem a quite drastic approximation, but experience has shown that this is not the case [36 -0]. The reason is that the ASA method very well captures those areas where the density is the highest, namely near the cores of the atoms. On the other hand, the valence region is characterized by a much smaller density and thus has no big influence on the MQSM so that the ASA approach is certainly viable from a computational point of view. 

Twenty years later, Isidor Traube, professor of physical chemistry at Berlin s Technische-Hochschule, distinguished between an inner atomic volume corresponding to the material core of the atom and an outer volume that included an atmosphere of bound ether the whole of the molecule then moved in a larger "co-volume" of free ether.41 Farther still from mainstream nineteenth-century chemistry, Karl Pearson developed a mathematical theory of "aether squirts," setting up a quantitative measure of chemical affinity in terms of the pulsation periods of the squirts.42... 

Before moving on to further discussions, we shall say a few words on dispersive or vdWs interactions. These are composed of an attractive force that arises from a sophisticated quantum-chemical short-range interaction of electrons, and an even shorter range, i.e., almost hard sphere repulsion of the cores of the atomic... 

We may disregard the closed-shell cores of the atoms since these play no role in the construction of symmetry-adapted wavefunctions, and concentrate attention upon the valence electrons. In the simplest case, with one valence electron per atom, we have a configuration 0102 n of N singly-occupied, non-degenerate valence orbitals which is then said to form a covalent structure for the molecule. Then under any spatial symmetry operation (%, a VB function Vsu-.k transforms as... 

The destructive power of nuclear weapons derives from the core of the atom, the nucleus. One type of nuclear weapon, the fission bomb, uses the energy released when nuclei of heavy elements such as plutonium fission (split apart). A second even more powerful type of nuclear weapon, the fusion or hydrogen bomb, uses the energy released when nuclei of hydrogen are united (fused together). 

Conventional, chemical explosives get their power from the rapid rearrangement of chemical bonds, the links between atoms made by sharing electrons. In chemical explosives, atoms dissociate from other atoms and form new associations this releases energy, but the atoms themselves do not change. Nuclear weapons are based on an entirely different principle. They derive their explosive power from changes in the structure of the atom itself, specifically, in the core of the atom, its nucleus. 

If you open the upper half of the doll, you will discover an identical, smaller doll inside. This doll represents the inner core of the atom, which consists of the nucleus and all electrons except the valence electrons. 

Because valence electrons are so important to the behavior of an atom, it is useful to represent them with symbols. A Lewis dot diagram illustrates valence electrons as dots (or other small symbols) aroimd the chemical symbol of an element. Each dot represents one valence electron. In the dot diagram, the element s symbol represents the core of the atom—the nucleus plus aU the inner electrons. The Lewis dot diagrams for several elements are shown in Figure 2.26. 

Reactions that involve the nucleus can occur. In fact, elements can be transformed into one another through these nuclear reactions. In the 20th century, people have found uses for nuclear chemistry that the alchemists never imagined. Now, you are about to explore how the tiny core of the atom can serve these useful functions. 

Nucleus The extremely small, positively charged core of the atom. 

Protons and neutrons are in a tiny core of the atom called the nucleus, which has a diameter of about 1/100,000 the diameter of the atom. The position and motion of the electrons are uncertain, but they generate a negative charge that is felt in the space that surrounds the nucleus. 

Valence electrons are those in the highest occupied energy level of an atom that are directly involved in the chemistry of the element. Alternatively, they are the electrons outside the noble gas core of the atom. 

One part of the splitting, due to the difference of the Coulomb integrals J, and Jv, can be easily interpreted as resulting from the difference in the interaction of an inner Is electron with an outer 2s electron or 2p electron. This effect was recognized in the days of the old quantum theory, being described as resulting from greater penetration of the core of the atom (the nucleus plus the inner electrons) by the more eccentric orbits of the... 

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