Electronegativity Scale Research Articles

Extending electronegativities to superheavy Main Group atoms

Abstract IUPAC recently published recommendations on rules for oxidation states within which was an endorsement of the electronegativity scale, called configuration energies, conceived by Allen and constructed from available calculated results. In conjunction with the International Year of the Periodic Table and the recognized extension of the Periodic Table through the end of its seventh period, it seemed timely to broaden those simple electronegativity calculations to include Main Group superheavy elements.

Evaluation of Electronegativity Scales.

Scales of electronegativity values are used by chemists to describe numerous chemical features such as chemical mechanisms, bond polarity, band gap, atomic hardness, etc. While the many scales provide similar trends, all differ in their predictive quality. Confirmation of the quality of a new scale often uses a previous scale for comparison but does not use independent means to demonstrate the merits of the scale. Utilizing a table of binary compounds of known ionic, covalent, and metallic bonding characters, a means to evaluate electronegativity scales is developed here. By plotting the electronegativity values of the two bonded atoms in binary compounds of a known bonding character, a tripartite separation results that generally divides the three bond types. Using the results of graphs of this sort, the success of bonding separations of 14 different scales of electronegativity has been evaluated on the basis of three quantitative parameters that can provide a measure of the quality of the scales. Three scales, those of Allen, Martynov and Batsanov, and Nagle, have been shown to be superior in their ability to predict the expected separation of bond types. Since this scheme successfully demonstrates the ability to evaluate the quality of electronegativity scales, it can be applied to other scales to establish their effectiveness in predicting bond types in binary compounds and thus the quality of the scales. This scheme is applied to a recently published electronegativity scale to evaluate the ability to determine its quality.

The covalent radii derived from the first-principle data

We present a collection of covalent radii for the elements H, B, C, N, O, F, Si, P, S, Cl, Ge, As, Se, Br, derived from the recently introduced systematic non-empirical dataset of the covalent bond lengths built basing on 26,050 molecular geometries and bond graphs obtained from quantum-chemical calculations using automated CLPO analysis with almost no input of empirical data. The obtained ‘non-empirical’ covalent radii, determined separately for single, double and triple bonds, have been found to be in good agreement with their empirical counterparts available in the literature. The distributions of deviations between the sum of proposed radii and the true bond lengths are analysed in details, with emphasis put on the role of the electron delocalisation on the bond lengths. Corrections to the additive covalent radii model due to the difference in the elements electronegativities are derived for Pauling electronegativity scale. We further assess the accuracy of distance-based discrimination between bonded and non-bonded pairs of atoms in which the interatomic threshold distance is parameterised via the found covalent radii.

A scale of atomic electronegativity in terms of atomic nucleophilicity index

Electronegativity (χ) is an important physico-chemical concept to study the chemical structure and reactivity. Although, the conundrum related to measurement of electronegativity still persists. In view of this fact, a simple yet rigorous scale of electronegativity (χ), invoking an inverse relationship with atomic nucleophilicity index (N), has been proposed for 103 elements of the periodic table. The computed data follows periodicity distinctly satisfying all the sine qua non of a standard scale of electronegativity. Further, electronegativity values display a sound similarity with the standard electronegativity scales validating the suitability of the proposed model. Molecular electronegativities of some polyatomic molecules have also been calculated using the proposed scale of electronegativity.

Electronegativity principles in metal oxides based supercapacitors

To meet growing demands for energy consumptions in modern society, it is necessary to develop different energy sources. Renewable energy such as wind and solar sources are intermittent, therefore, energy storage devices become more and more important to store energy for use when no wind or no light. Supercapacitors play a key role in energy storage, mainly due to their high power density and long cycling life. However, supercapacitors are facing the obstacle of low energy density, one of the most intensive approaches is to rationally design new electrode materials. In this review, we focus on metal oxides-based materials and present an electronegativity criterion for the design and appropriate selection of new electrode chemical compositions. Metal elements with proper electronegativity scale have the potential to transfer electron for energy storage. Suitable positive and negative electrodes matching can enhance many properties of supercapacitors, which may overcome many related obstacles. Furthermore, electronegativity scale may also help people to find novel metal oxides based supercapacitors.

ELECTRON STRUCTURE OF RADICALS OF SULFOXYLIC ACID ESTERS

The density functional theory B3LYP/6-311++G(3df,3pd) has been used to optimize the geometry of homologues of a series of sulfoxylic acid ester radicals and to obtain the electron density distributions of the first nine compounds. The hydrogen bond presented in the initial molecules of the unbranched esters of sulfoxylic acid between the hydrogen of the second carbon atom of the alkyl chain (from the ester bond) and the oxygen of the hydroxyl group of the sulfur-containing fragment (-C(Н)H-CH2-O-S-ОН) and the corresponding cycle are not observed in the radicals. The fragmentation of the structures into topological groups of CH3, CH2, and (-O-S-O)● has been proposed and their electron integral characteristics are presented including charges, unpaired electron density, energy, and volume. The steric effect of the fragment (-O-S-O)● has been established and its inductive effect has been considered based on the groups charge parameters changes triggered by an increase in the hydrocarbon chain. The scale of group electronegativities of the studied homologues has been constructed by comparing the charges of topological groups. The fact that the radical center corresponds to the fragment (-O-S-O)● has been demonstrated by the spin density delocalization results (having the largest fraction on the sulfur atom (0.57), slightly less fraction on the oxygen atom with a free valence (0.32) and an insignificant fraction on oxygen atom using the ether bond (0.10)). The increment value of the total energy contributed by the CH2 group of each subsequent homologue of the series under the study has been estimated. It is 103260 kJ/mol. The evaluation of the “standard” value of the groups’ total electron energy and the use of their relative energy (ΔE(R)) for comparing with ΔE(R) of molecules and radicals of other homologous series have been described. A decrease in the volumes of the two closest to the sulfur-containing fragment CH2 groups caused by an outflow of electron density from them toward the fragment (-O-S-O)● has been noted.

Incompatible models in chemistry: the case of electronegativity

During the second half of the nineteenth century, electronegativity (EN) has been one of the most relevant chemical concepts to explain the relationships between chemical substances and their possible reactions. Specifically, EN is a property of the substances that allows them to attract external electrons in bonding situations. The problem arises because EN cannot be measured directly. Indeed, the only way to measure it is through different properties that do can be directly measured, for instance enthalpy, ionization energies or electron affinities. What is particularly troubling about this case in quantum chemistry is that the different models used to describe and quantify EN are incompatible but, in a certain sense, equivalent because the same EN scale results in all of them. By analyzing Linus Pauling’s and Robert Mulliken’s models of EN, it will be argued that, if we remain cling to a traditional representative conception of models, we cannot understand the meaning of the information provided by those models. Indeed, if we do not want to adopt an instrumentalist point of view concerning chemical knowledge, we should reconsider by virtue of what a model represents the system, or, in other words, which the factors that determine the representative power of a model are. I will propose a new perspective that incorporates the role of experimental techniques in the very notion of representation; this perspective allows us to understand how supposedly incompatible models of the same target system can be both simultaneously representative.

ELECTRON PARAMETERS OF 1,1,1 – TRILUOROALKANES

On the basis of quantum-chemical calculations the properties of trifluoro-substituted hydrocarbon molecules CnH2n+1-CF3 (n ≤ 9) received from their electron density distribution were considered. The geometry optimization of ten structures was carried out. The surfaces of zero flow electron charge density gradient were specified, and the basins of atomic groups and fluorine atoms were found. The electron integral parameters (charges q(R), energies E(R) and volumes V(R)) of atomic groups in trifluoroalkane molecules were calculated and analyzed. The relationship between the length of the hydrocarbon chains and the transferability of the properties of the selected groups (CF3, CH3, CH2) was revealed, that is reflected in their transferable parameters. For the studied homologous series the qualitative group electronegativity scale was made up and inductive effect (I - effect) of fluorine containing group was considered. The attenuation of I – effect in CnH2n+1-CF3 (n ≥ 6) within molecular fragments CF3-(CH2)4 and CH3-CH2 was identified. In this regard, the appearance of the «unperturbed» CH2 group was registered at n > 6. The «standard» (or «transferable») value of the total group energy E(R) was introduced and computing of the relative group energy ΔE(R) was described. It was shown, that the reduction of the volumes of the nearest СН2 to the СF3 was caused by the electron density redistribution. The comparative analysis of the group charges q(R) in CnH2n+1-CF3 (n ≤ 9) with corresponding q(R) in monofluorine alkanes, monofluorine alkane radicals, difluorine alkanes and difluorine alkane radicals was performed. The comparison of the charges of relevant groups and fluorine-containing fragments of the fluoro-substituted nonane and their radicals was presented as graphic dependence, which provides an understanding of the attenuation of I – effect from СF3.

Electronegativity Seen as the Ground-State Average Valence Electron Binding Energy.

We introduce a new electronegativity scale for atoms, based consistently on ground-state energies of valence electrons. The scale is closely related to (yet different from) L. C. Allen's, which is based on configuration energies. Using a combination of literature experimental values for ground-state energies and ab initio-calculated energies where experimental data are missing, we are able to provide electronegativities for elements 1-96. The values are slightly smaller than Allen's original scale, but correlate well with Allen's and others. Outliers in agreement with other scales are oxygen and fluorine, now somewhat less electronegative, but in better agreement with their chemistry with the noble gas elements. Group 11 and 12 electronegativities emerge as high, although Au less so than in other scales. Our scale also gives relatively high electronegativities for Mn, Co, Ni, Zn, Tc, Cd, Hg (affected by choice of valence state), and Gd. The new electronegativities provide hints for new alloy/compound design, and a framework is in place to analyze those energy changes in reactions in which electronegativity changes may not be controlling.

Electronegativity scales and electronegativity-bond ionicity relations: A comparative study

Electronegativity (χ) and bond ionicity are very important concepts in chemistry and other branches of science. Due to the lack of a precise definition, several χ scales have been introduced, based on a variety of chemical and physical quantities. On the other hand, many empirical relations have been devised to estimate the bond ionicity from χ of the bonding atoms. In this work, the bond ionicity in an extensive list of ANB8−N compounds, obtained by employing the Abu-Farsakh and Qteish ionicty scale (qi), are used as a benchmark to investigate the performance of the widely accepted and promising χ scales and frequently adopted χ-ionicity relations. The employed ionicty scale is based on the centers of the maximally localized Wannier functions and has several advantages. It has been demonstrated that the bond ionicity is better expressed in terms of normalized Δχ, rather than Δχ, and the best χ-ionicity relation has been unambiguously identified. The Allred-Rochow (AR) electronegativity scale is found to outperform the other considered electronegativity measures. The discrepancies between qi and bond ionicity (pi), obtained by using the best χ-ionicity relation and the AR scale, are found to have clear trends, which may imply that the AR values of some atoms are inaccurate. Corrections to the AR values, to minimize the discrepancies between qi and pi, lead to a highly reasonable set of χ values of the involved atoms that satisfy the main χ rules.

Electronegativity and enthalpy of mixing biplots for High Entropy Alloy solid solution prediction

Analysis of the applicability of different electronegativity scales (XAllen, XPauling, and XMulliken) as a replacement for the empirical valence electron concentration (VEC) parameter to determine High Entropy Alloy (HEA) solid-solution stability is performed, using statistical methods (via cluster analysis and probability density function). The analysis is conducted on a dataset consisting of 617 entries. The results show that XAllen is better suited to predict solid-solution stability when utilising only one parameter. However, substituting XAllen for XMulliken offers better prediction in a biplot with the enthalpy of mixing (ΔH). An analysis of the VEC-ΔH biplot shows that phase separation in the biplots can be attributed to changes in the electronic structure.

Charge-Shift Corrected Electronegativities and the Effect of Bond Polarity and Substituents on Covalent-Ionic Resonance Energy.

Bond dissociation energies and resonance energies for HnA-BHm molecules (A, B = H, C, N, O, F, Cl, Li, and Na) have been determined in order to re-evaluate the concept of electronegativity in the context of modern valence bond theory. Following Pauling's original scheme and using the rigorous definition of the covalent-ionic resonance energy provided by the breathing orbital valence bond method, we have derived a charge-shift corrected electronegativity scale for H, C, N, O, F, Cl, Li, and Na. Atomic charge shift character is defined using a similar approach resulting in values of 0.42, 1.06, 1.43, 1.62, 1.64, 1.44, 0.46, and 0.34 for H, C, N, O, F, Cl, Li, and Na, respectively. The charge-shift corrected electronegativity values presented herein follow the same general trends as Pauling's original values with the exception of Li having a smaller value than Na (1.57 and 1.91 for Li and Na respectively). The resonance energy is then broken down into components derived from the atomic charge shift character and polarization effects. It is then shown that most of the resonance energy in the charge-shift bonds H-F, H3C-F, and Li-CH3 and borderline charge-shift H-OH is associated with polarity rather than the intrinsic atomic charge-shift character of the bonding species. This suggests a rebranding of these bonds as "polar charge-shift" rather than simply "charge-shift". Lastly, using a similar breakdown method, it is shown that the small effect the substituents -CH3, -NH2, -OH, and -F have on the resonance energy (<10%) is mostly due to changes in the charge-shift character of the bonding atom.

Nucleation-dependant chemical bonding paradigm: the effect of rare earth ions on the nucleation of urea in aqueous solution.

Rare earth ions can be used to construct a variety of novel structures and are favorable to chemical bonding regulation and design. In this study, the chemical bonding paradigm between rare earth ions (Ln3+) and urea molecules in an aqueous solution can be tracked by the evolution of C[double bond, length as m-dash]O, NH2, and CN vibration bands during the urea nucleation stage. Rare earth ions such as La3+, Gd3+, and Lu3+ can manipulate the nucleation time of urea via regulating the nucleation-dependant N-C[double bond, length as m-dash]OH-N hydrogen-bonding between urea molecules. Two types of chemical bondings between Ln3+ and urea molecules have been confirmed, which are Ln3+O[double bond, length as m-dash]C-N and Ln3+NH2-C. Compared with Ln3+NH2-C, Ln3+ prefers to coordinate with the O[double bond, length as m-dash]C bond in urea. With a higher concentration of rare earth ions in the solution, some N-C[double bond, length as m-dash]OH-N hydrogen bonds are broken as a consequence of the incorporation of Ln3+ into the lattice, resulting in the decreased symmetry of local urea molecules in the crystalline nuclei and the consequent Ln3+ concentration-dependent nucleation time of urea. Moreover, using the ionic electronegativity scale of Ln3+, the different effects of La3+, Gd3+, and Lu3+ on urea nucleation can be further distinguished. The present study provides basic data for unrevealing the chemical bonding regulation role of rare earth ions in the formation of hydrogen bonded materials, which may give insight into the design and fabrication of novel materials utilizing rare earth ions to adjust the chemical bonding process.

Using the centre-of-mass of localized electron pairs to quantify electronegativity

Localized electron pair densities are explored with the purpose of developing a relationship between properties of the electron pair centre-of-mass and atomic electronegativities. These electron pair centre-of-mass densities are determined for the localized molecular orbital representing the A–H bond in a compound AHn (where n = 1–4) for each of the first and second row atoms with available valence sites. By analyzing the topography of these densities, we observe the migration of the electron pair as the electronegativity of atom A changes. We demonstrate strong linear correlations between features of these centre-of-mass densities and various empirically based electronegativity scales, all of which are defined in significantly different ways. Based on strong agreement with past electronegativity scales, we propose the use of localized electron pair centre-of-mass densities as a simple and intuitive theoretical model for electronegativity. We have presented our own electronegativity scale, employing Pauling units as is common amongst many existing scales.

A generalized model for predicting the thermodynamic properties of clay minerals

A set of models for estimating the enthalpy of formation, the entropy, the heat capacity and the volume of dehydrated phyllosilicates is presented. The model for entropy and heat capacity estimation is essentially based on a method of decomposition into polyhedral units, similar to that published by Holland (1989). The model for predicting the enthalpy of formation is based on the electronegativity scale, as previously developed by Vieillard (1994a, 1994b). For the sake of consistency, the models are parameterized using the same critical selection of thermodynamic properties from the literature. This includes a set of direct measurements especially dedicated to clay minerals that had not been taken into account in previous calculation methods. The accuracy of the predictions is tested for each property. The verification tests are also carried out for minerals that include different chemical elements than the phases used to derive the model constants, especially lithium-bearing micas. Verification tests also concern the Gibbs energy function that combines contributions from both models. Finally, the models are used in order to propose a complete thermodynamic database for clay mineral end-members. The consistency of the stability domains calculated on the basis of these thermodynamic properties is investigated by drawing relevant predominance diagrams for some chemical systems of interest. The models proposed represent a significant improvement with respect to previous works as regards the global accuracy of the estimates and because the developments were realized and tested using the same set of minerals, whose properties had been collected through a critical selection of the literature.

The importance of being chemical affinity. Part VI: The harvest

The quantitative scale of electronegativity, obtained by Linus Pauling, as a result of qualitative electron affinity background, generated multiple different and interesting proposals until today, which have proved to be the effort of ingenuity to get a universal concept of affinity, which has resulted incomplete. Thermodynamics, specifically its thermochemical branch, has offered an explanation, which has been accepted by The International Union of Pure and Applied Chemistry (IUPAC), as incomplete as the former. In both cases, it is thought that the error is in regard to affinity as a property, rather than a behavior.

First-principles study on stability of transition metal solutes in aluminum by analyzing the underlying forces

Although there have been some investigations on behaviors of solutes in metals under strain, the underlying mechanism of how strain changes the stability of a solute is still unknown. To gain such knowledge, first-principles calculations are performed on substitution energy of transition metal solutes in fcc Al host under rhombohedral strain (RS). Our results show that under RS, substitution energy decreases linearly with the increase of outermost d radius rd of the solute due to Pauli repulsion. The screened Coulomb interaction increases or decreases the substitution energy of a solute on condition that its Pauling electronegativity scale ϕP is less or greater than that of Al under RS. This paper verifies a linear relation of substitution energy change versus rd and ϕP under RS, which might be instructive for composition design of long life alloys serving in high stress condition.

The noble gases: how their electronegativity and hardness determines their chemistry.

The establishment of an internally consistent scale of noble gas electronegativities is a long-standing problem. In the present study, the problem is attacked via the Mulliken definition, which in recent years gained widespread use to its natural appearance in the context of conceptual density functional theory. Basic ingredients of this scale are the electron affinity and the ionization potential. Whereas the latter can be computed routinely, the instability of the anion makes the judicious choice of computational technique for evaluating electron affinities much more tricky. We opted for Puiatti's approach, extrapolating the energy of high ε solvent stabilized anions to the ε = 1 (gas phase) case. The results give negative electron affinity values, monotonically increasing (except for helium which is an outlier in most of the story) to almost zero at eka-radon in agreement with high level calculations. The stability of the B3LYP results is successfully tested both via improving the level of theory (CCSD(T)) and expanding the basis set. Combined with the ionization energies (in good agreement with experiment), an electronegativity scale is obtained displaying (1) a monotonic decrease of χ when going down the periodic table, (2) top values not for the noble gases but for the halogens, as opposed to most (extrapolation) procedures of existing scales, invariably placing the noble gases on top, and (3) noble gases having electronegativities close to the chalcogens. In the accompanying hardness scale (hardly, if ever, discussed in the literature) the noble gases turn out to be by far the farthest the hardest elements, again with a continuous decrease with increasing Z. Combining χ value of the halogens and the noble gases the Ng(δ+)F(δ-) bond polarity emerging from ab initio calculations naturally emerges. In conclusion, the chemistry of the noble gases is for a large part determined by their extreme hardness, equivalent to a high resistance to change in its electronic population coupled to their high electronegativity.

Шкала электроотрицательностей сульфиновых кислот

Шкала электроотрицательностей сульфиновых кислот

The importance of being chemical affinity. Part V: The fruits

Through the meticulousness in experimentation, the incorporation of discoveries in physics and the application of the logic of algebra to make chemistry´s language systematic and universal, the level of thought achieved in chemistry during 18th century gave a foundation to the discipline that would allow it to evolve and transform. The discovery, comprehension and application of electricity in the 19th century supplied chemistry with analogous units, which in turn, facilitated increased understanding of the field and permitted the proposal of new theories. Developments in thermodynamics allowed for the presentation of qualitative scales of affinity and electronegativity. The discovery of the atom and electron and the emergence of quantum physics restructured chemical thought, permitting for the establishment, in the first half of the 20th century, of the first quantitative scale of electronegativity, which offered chemistry a new dynamism, facilitating the proposal of other scales, based on diverse approaches.