Nonvalence electrons

Quantum Free-Electron Theory Constant-Potential Model, The simple quantum free-electron theory (1) is based on the electron-in-a-box model, where the box is the size of the crystal. This model assumes that (1) the positively charged ions and all other electrons (nonvalence electrons) are smeared out to give a constant background potential (a potential box having a constant interior potential), and (2) the electron cannot escape from the box boundary conditions are such that the wavefunction if/ is... 

Why are the properties of elements within a group similar hut not identical Although elements within a group have the same number of valence electrons, they have different numbers of nonvalence electrons. Remember what happens as the atomic number increases within a group. As new levels of electrons are added, the atomic radius increases and the shielding effect increases. As a result, the ionization energy decreases. A lower ionization energy makes it easier for an element to lose electrons. 

Huckel (properly, Huckel) molecular orbital theory is the simplest of the semiempirical methods and it entails the most severe approximations. In Huckel theory, we take the core to be frozen so that in the Huckel treatment of ethene, only the two unbound electrons in the pz orbitals of the carbon atoms are considered. These are the electrons that will collaborate to form a n bond. The three remaining valence electrons on each carbon are already engaged in bonding to the other carbon and to two hydrogens. Most of the molecule, which consists of nuclei, nonvalence electrons on the carbons and electrons participating in the cr... 

The use of abbreviated electron configurations, in addition to being faster and easier to write, serves to highlight the valence electrons, those electrons involved in bonding. The s)unbol of the noble gas represents the core, nonvalence electrons and the valence electron configuration follows the noble gas s)unbol. 

To draw Lewis structures, we first write the chemical symbol of the atom this symbol represents the nucleus and all of the lower energy nonvalence electrons. The valence electrons are indicated by dots arranged around the atomic symbol. For example ... 

First, we present a particular basic molecular system which is used for approximate applications in chemical kinetics. The presumption is that many other real systems have some of the character present in this basic system, which we now elaborate. Suppose we have n valence electrons and v nuclei, where n = r, and one valence electron is on each nucleus. Valence electrons may be regarded as those which enter more specially into bonding and therefore into a chemical reaction. Further, all the electrons will be in equivalent states. This latter provision means, for example, that all the coefficients of the terms in Eq. (80) are equal except for sign, and that and differ from each other only in interchange of equivalent nuclei. It should be noted that if we apply the results derived below to complex systems, i.e., not hydrogen atoms, we have made the doubtful assumption that we may ignore nonvalence electrons. Moreover, the equivalence of the electronic states imphes that we may treat complex systems as if all the valence electrons were in some particular state such as the Is state. 

Write the electron configuration for silicon. Identify the valence electrons in this configuration and the nonvalence electrons. From the standpoint of chemical reactivity, what is the important difference between them ... 

The chemical reactivity of the elements is largely determined by their valence electrons, which are the outermost electrons. For the representative elements, the valence electrons are those in the highest occupied n shell. All nonvalence electrons in an atom are referred to as core electrons. Looking at the electron configurations... 

The heat of formation is the energy released as heat when atoms situated at theoretically infinite distance approach, bind, and form the molecule of interest. The core includes, by definition, the atomic nucleus and the electrons that do not participate in chemical bonds, that is, the nonvalence electrons. The semiempirical method PM6 estimates the heat of formation as the sum of the total repulsion energy of the cores and the total heat of formation of the atoms. Each semiempirical quantum mechanics method calculates, in its own manner, the energy of repulsion of the cores and utilizes a different set of values for the atomic heat of formation. Consequently, the values of the heat of formation determined for the same molecule by different semiempirical... 

Because elements in a given group have the same number of valence electrons, they have similar properties. The properties are not identical, however, because the numbers of nonvalence electrons differ. For example, the ionization energy of elements in a group decreases as the atomic number increases. For that reason, metals, which tend to lose electrons when they react, increase in reactivity as the atomic number increases. Nonmetals, which tend to gain electrons, decrease in reactivity as the atomic number increases. 

---