Electron convention

In conclusion, A[ //°(AB+,g) calculated by the electron convention will be 6.197 kJ mol-1 higher (at 298.15 K) than the value derived by the ion convention. In practical terms, this indicates that we must be alert when using enthalpy of formation data from several sources because they may have been derived by accepting either one of those conventions. 

When comparing literature data for the quantities addressed in this section, it is therefore essential to check if those data are consistent, that is, if they are based on the same value for the anchor. On the other hand, note that proton affinity, basicity, and acidity values do not depend on whether we follow the electron convention, the ion convention, or the electron FD convention. This is clearly evidenced by reactions 4.25 and 4.27, which do not involve the electron as a reactant or product species. However, it is also obvious that the values of the standard enthalpies of formation of AH+ and A-, calculated from PA(A) and A acid-7/0 (AB), respectively, will vary with the convention used to derive the standard enthalpy of formation of the proton. 

In the first case, the threshold equals the bond energy, D(AX —X). In the second case, the threshold equals the differences in the product and reactant heats of formation such that Z)(yf+ — B) = D BC) — Eq. When the threshold analysis is performed using Eq. (2), all sources of reactant energy are included, such that the bond energies so determined correspond to thermodynamic values at OK (Dalleska et al., 1993 Armentrout and Kickel, 1996). Conversion to 298-K values can be achieved using standard thermodynamic functions. In this work, 298-K heats of formation for ions are reported using the thermal electron convention. Values fi om the literature that use the stationary electron convention should be increased by 0.064 eV for comparison to these values. 

Values reported here differ from those in the original citations as discussed in the text, Sections II.D.3 and IV.C. Ion heats of formation use the thermal electron convention, Boo eta/., 1990. Wlodek e/a/. 1991. Kickel et al., 1992. Shiner al., 1990. Estimated in Walsh, 1981. i- Allendorf and Melius, 1992. Shin and Beauchamp, 1989. Raghavachari, 1988b. 

The negative value of the enthalpy change for Equation 8 when n = 0 is defined (7) as the electron affinity (EA) of the oxidized species when the oxidized and reduced species are in their ground rotational, vibrational and electronic states (0 K). At any temperature for any value of n (0, positive, or negative), the thermodynamic state functions for l uation 8 are given by aX (X = G, H, or S), and the thermochemistry of electron attachment can be defined in the ion convention ("stationary electron convention") (7). The relationship between EA and aG is given by Equation 9. A similar relationship applies for adiabatic ionization energies. 

The chemical constitution of an EM(.4) is determined by the set of the cores of A and the distribution of the valence electrons. In our present model concept the valence electrons are either pairwise shared by pairs of cores and form covalent bonds, or occupy valence orbitals of individual atoms as lone electrons. Thus the chemical constitution of an EM(AL) is given by its covalent bonds and bonded neighbors, and its lone valence electrons. Conventionally, this is represented by the constitutional chemical formulas. 

Finally, when using a database with enthalpies of formation of ions, one should be aware of the two possible conventions used to derive those values the so-called thermal electron convention or just electron convention, and the stationary electron convention or the ion convention. These conventions are related to the standard enthalpy of formation of an electron gas Af//°(e , g) and its thermal temperature correction from 0 to 298.15 K. A detailed description of the reasoning behind both conventions provided in the introductory chapter of a widely used data compilation. In practical terms, one should be aware that the enthalpy of formation of an ion calculated by the electron convention will be 6.197 kj mol (= 2.5RTat 298.15 K) higher than the value derived by the ion convention. Therefore, we must be alert when using enthalpy of formation data from several sources, because they may have been derived by accepting either of those conventions. 

Organic electronics has great potential and roadmapping future developments and trends is an ongoing task and key activity of the OE-A and its members. The next update of the roadmap was published in June 2009 at OE-A s annual conference and exhibition LOPE-C - Large-area, Organic and Printed Electronics Convention. 

In view of the discovery of Brockway and Cross that the nickel-carbon bond in nickel carbonyl has a large amount of double bond character, we may well expect this to be the case for the iron-carbon bond in carbonmonoxyhemoglobin also, the double bond being formed with the use of a pair of electrons conventionally assigned to the iron atom as 3d electrons. To carbonmonoxyhemoglobin there would then be ascribed the resonating structure ... 

The standard electrode potential convention is a different approach from that normally taken with thermodynamic quantities related to chemical change in electron number for gas-phase molecules and ions. Ionization potentials and electron affinities are referenced to the electrostatic zero potential energy of the infinitely separated electron in a field-free vacuum." The electron itself is conventionally treated as an ideal gas (the thermal electron convention) or as a subatomic particle with no heat capacity or entropy (the ion convention). lonization/electron attachment enthalpies under the two conventions differ by 1.48kcalmoU at 298 K," while the corresponding free energies under the two conventions are only equal at 0 K and 297 K. ... 

The evaluation of this expression for an ionization process, in which an electron appears explicitly as a reactant or product, requires a consistent approach. In the Electron Convention, used predominantly in the thermodynamics community, and the Ion Convention, employed in the ion physics/chemistry communities, important differences... 

At temperatures above 0 K, e.g., 298 K, where many standard thermochemical data are reported, the Electron and Ion conventions differ in the following manner in the Electron Convention, the electron is treated like a standard chemical element, and its enthalpy of formation is constrained to be zero at all temperatures. However, the integrated heat capacity is not taken to be zero. Under this condition, the expressions for the enthalpies of formation of positive and negative ions reduce to... 

In these expressions, C is the integrated heat capacity for the electron. The integrated heat capacities for the ion M+ and its precursor neutral M effectively cancel in the above expressions. The Electron Convention has been used historically in the ion thermochemistry literature despite the fact that the additive correction to the enthalpy of ionization from the integrated heat capacity of the electron is small and temperature dependent, thereby causing confusion. 

The calculation of C, the integrated heat capacity of the electron, is based on treating the free electrons as an ideal gas and computing the heat capacity according to Boltzmann statistics. At 298 K, the heat capacity at constant pressure is that of an ideal gas, C = 5/2 RT, or 6.197 kJ/mol. This computation allows data tabulated under the Electron Convention to be rationalized with Ion Convention data as follows ... 

While many earlier compilations of data have used the Electron Convention, the most recent tabulation of standard enthalpies described in the NIST Webbook (http //www.nist.gov) employs the Ion Convention. It does not introduce any temperature dependence, however small, to ion enthalpies of formation and is, therefore, considered a simpler and less confusing representation of data. This convention is also consistent with the literature of the ion physics and chemistry community over the past 50 years. In any application of tabulated thermochemical data, investigators are cautioned to be exceedingly clear about the conventions of the data they employ. 

In eq 5, AHjo, (gas) is the corrected gas phase ionization potential of the nucleotide, or cluster, and ASjon Cs ) e change in entropy associated with ionization in the gas phase. Compared to AHj<, ij(gas), TAS i (gas) is negligible, so that AGj (gas) AHio i2(gas). This approximation is supported by the observation that, by electron convention Fermi-Dirac statistics, TAS for the ionization of a hydrogen atom at room temperature is 0.05 eV (44). In this investigation, the values of IP employed in eq 5 were the values of IPcorr(i) obtained via eq 1. 

S. J. Garlock, Characteristics of Lithium Solid State Batteries in Memory Circuits, Wescon 81, San Francisco, Calif., Professional Program Session Rec. 29, Electronic Conventions, Inc., El Se-gundo, Calif., Sept. 1981. 

Eor threshold studies it is convenient to consider the ejected electron at rest at all temperatures, i.e. AEff(e ) = 0. This stationary electron convention is... 

There are two different conventions used in ion thermochemistry, the so-called electron convention and the ion convention [2, 128]. They differ in the treatment of the electron captured or liberated during ion formation. In the electron convention, the electron is treated as an element of enthalpy ... 

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