Electron affinity rule

Tables 2.1, 2.2, 2.3 and 2.4 give data for atomic radii, ionisation energies and electron affinities which allow these rough rules to be justified.

Similar calculations were made for the only possible isomer of C70 [11-13] that obeys the isolated pentagon rule [4, 6] and for some of the most stable isomers of the higher fullerenes [11, 14-16]. On the basis of their easily accessible LUMOs and high electron affinities, all stable members of the fullerene family were expected to display very rich cathodic electrochemistry. 

In die Pople family of basis sets, the presence of diffuse functions is indicated by a + in die basis set name. Thus, 6-31- -G(d) indicates that heavy atoms have been augmented with an additional one s and one set of p functions having small exponents. A second plus indicates the presence of diffuse s functions on H, e.g., 6-311- -- -G(3df,2pd). For the Pople basis sets, die exponents for the diffuse functions were variationally optimized on the anionic one-heavy-atom hydrides, e.g., BH2 , and are die same for 3-21G, 6-3IG, and 6-3IIG. In the general case, a rough rule of thumb is diat diffuse functions should have an exponent about a factor of four smaller than the smallest valence exponent. Diffuse sp sets have also been defined for use in conjunction widi die MIDI and MIDIY basis sets, generating MIDIX+ and MIDIY-I-, respectively (Lynch and Truhlar 2004) the former basis set appears pardcularly efficient for the computation of accurate electron affinities. 

Ionic bonds are formed by electrostatic attractions between oppositely charged ions. These ions are formed when atoms of low ionization energy (weak attraction for valence electrons) lose one or more electrons to atoms with high electron affinity (strong attraction for electrons). At this point, we can use the octet rule to guide us through the process. 

Out of the multiplicity of catalytic processes, Roginskii has segregated two large groups (1) those processes characterized by electronic transitions and (2) those in which the acidic properties of the catalyst are important. Thus more restrictive conditions on the nature of the process make it possible to associate the catalytic activity with certain physical attributes such as color, electrical conductivity, and electron affinity. Consequently a number of simple rules for the selection of catalysts can be stated. The following characteristics have been noted (1) pronounced effects are noted with highly colored compounds (2) catalysts containing transition elements are exceptionally active and (3) white compounds do not have a pronounced catalytic effect. 

Electronegativity relates to ionization potential for cations, or electron affinity for anions. Pauling s general rule on bonding states that ions of closer electronegativity have a greater tendency to form covalent bonds, (NaCl = 2.1) < (CaS = 1,5) < (CuS = 0.5) < (CS = 0) (Table 3A). Ionic radii and electronegativities permit the formulation of some specific rules about chemical bond formation. 

The chemical counterpart of the roof will be a set of valence-shell electrons, and we shall look at atomic and molecular architectures that can be hosted under such a roof when bringing in stable nuclei and corresponding core electrons. In order to see what happens with such an idea in a Chemical Aufbau approach, let us start with an octet of electrons under which we place a nucleus with atomic number Z = 10 and a K-shell with two core electrons. The result is a neon atom, an exceptionally stable architecture with spherical (three-dimensional) symmetry. The same result would happen for Z = 18 (argon) with one more "floor", and so on or the following noble gas atoms. Actually, we start with the closed electronic shells allowed by the Pauli Exclusion Principle and the "n ( Rule", and we supply the nuclei corresponding to such shells. The proof for the stability of this architecture is provided by the high ionization potential and the low electron affinity. 

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