Electron attachment energies

V.I. Vedeneev, L.V. Gurvich, V.N. Kondratyev, et al.. Handbook of Energies of Breaking of Chemical Bonds. Ionization Potential and Electron Attachment Energies, Kondratyev,V.N. (ed.), USSR Acad, of Sci. Publ., Moscow, 1962 (in Russian). 

Figure 1 shows the electron attachment energies (AE) and ionization potentials (IP) of silyl substituted 7t-systems and related compounds [4], AE can be correlated with the energy level of the LUMO (lowest unoccupied molecular orbital) and IP can be correlated with the energy level of the HOMO (highest occupied molecular orbital). For a-substituted 7t-systems, the introduction of a silyl group produces a decrease in the tc -(LUMO) level. This effect is attributed to the interaction between a low-lying silicon-based unoccupied orbital such as the empty d orbital of silicon and the it orbital (d -p interaction) as shown in Fig. 2. Recent investigations on these systems, however, indicate that d orbitals on silicon are not necessarily required for interpreting this effect a-effects of SiR3 can also be explained by the interaction between Si-R a orbitals and the 7r-system.

SiM 3 Fig. 1. Correlation diagram giving electron attachment energies (AE) and ionization potentials (IP) of a-,—SiMe3 and jS-silyl substituted ethylenes... 

This section summarizes the variation, across the periods and down the groups of the Periodic Table, of (i) the ionization energies, (ii) the electron attachment energies (electron affinities), (iii) the atomic sizes and (iv) the electronegativity coefficients of the elements. 

Figure 1.4 The first ionization 1.6.2 Variations in Electron Attachment Energies...

The electron attachment energy or electron affinity is defined as the change in internal energy (i.e. A U) that occurs when one mole of gaseous atoms of an element are converted by electron attachment to give one mole of gaseous negative ions ... 

The first electron attachment energies of the first 36 elements are plotted in Figure 1.5 and show the values for H and He followed by a characteristic pattern, the second repetition of which is split by the values for the 10 transition elements. The value for hydrogen is -72.8 kJ mol, which is very different from the Is orbital energy of -1312 kJ mol-1 because of the interelectronic repulsion term amounting to -72.8 -... 

Figure 1.5 The electron attachment energies of the first 36 elements...

The trends in first ionization energies, first electron attachment energies, atomic sizes and electronegativity coefficients of the elements across the groups and down the periods of the periodic classification. 

What general trends are noticeable across the Periodic Table in the values of (a) the first ionization energies, (b) the first electron attachment energies, and (c) the covalent radii of the elements ... 

The effects are observable by a comparison of the metallic radii, the first three ionization energies and the first electron attachment energy of the Group 11 elements as shown in Table 7.3, and the metallic radii and the first two ionization energies of the elements of Group 12 (Zn, Cd and Hg) as given in Table 7.4. 

Table 7.3 The metallic radii, first three ionization energies and first electron attachment energies of the Group 11 elements (energies in kJ mol-1)...

The / terms are the successive ionization energies of the element M, and the E term is the electron attachment energy of the element X. 

The overall change of enthalpy represents the enthalpy of formation of the hydrated anion, X (aq), and has a value as given in Table 2.2 for particular cases. The value consists of contributions from enthalpy of atomization of element M and its electron attachment energy, and the enthalpy of hydration of the gaseous ion. It also includes the enthalpy of ionization of the hydrogen atom, the enthalpy of atomization of dihydrogen and the enthalpy of hydration of the proton. The enthalpy of formation of the anion is estimated by the equation ... 

Burrow, P. D., K. Aflatooni, and G. A. Gallup, Dechlorination rate constants on iron and the correlation with electron attachment energies , Environ. Sci. Technol., 34, 3368-3371 (2000). 

Among the nudeobases, Thy and Cyt are most readily reduced (Table 10.2). Electron attachment energies have been determined in the gas phase (Aflatooni et al. 1998), and they confirm this view. Theoretical vertical attachment energy calculations rank the nudeobases in the order Ura < Thy < Cyt < Ade < Gua (Sevilla et al. 1995). 

Ionisation potentials and electron affinities (or ionisation energies and electron-attachment energies)... 

It has the usual energy units of kJmol-1, and differs in sign from the electron affinity for example, the electron affinity of the H atom is 0.75 eV, but the electron attachment energy of H(g) is -73 kJ mol-1. In order to convert electron attachment energies from A U° quantities at 0 K to AH" quantities at 298 K, it is necessary to make a correction ... 

The first of these involves the removal of two electrons from zinc atoms in the gas phase, and A/f° for the process will be equal to the sum of the first and second ionisation enthalpies of Zn(g), designated /, and /2 respectively. For the second process, AH° will be equal to twice the electron attachment enthalpy of H+(g) (which is the same as —21, where / is the ionisation enthalpy of atomic hydrogen). Obviously, we could use ionisation and electron attachment energies (instead of enthalpies), without correction for the RT terms which cancel out when we sum up the enthalpy changes for all the steps in the analysis. Thus for the process ... 

AH° is equal to the sum of the appropriate ionisation and electron attachment energies and the corresponding enthalpies need not be explicitly considered. Throughout this book, ionisation and electron attachment energies may, where appropriate, masquerade as enthalpies on the understanding that the RT corrections which ought to have been made ultimately cancel. 

Table 4.4 Electron attachment energies (in kJ mol ) for Main Group atomic substances...

Second electron attachment energies E2 are the values of AC0 at absolute zero for the process ... 

Finally in this section, we should note the relatively exothermic electron attachment energies of Cu, Ag and Au —118, —126 and... 

The atomisation enthalpy of elemental sodium Afl%tom, the first ionisation energy of atomic sodium Iu the dissociation enthalpy D of gaseous chlorine, the electron attachment energy Ex of atomic chlorine and the enthalpy of formation A//)1 of crystalline sodium chloride can all be taken from standard tabulations of experimental data. An experimental lattice energy UL is thus given by ... 

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