La naturaleza del enlace químico 2013 ¡No existe tal cosa llamada orbital!

Despite the fact that the chemical bond is a fiction, although convenient and nearly harmless, it plays an enormous role in the thinking, and especially the education, of chemists at all levels. Much further fiction has accumulated during the past 85 years; although, when the ideas about bonds, orbitals, hybridization and related topics originated and became widely known, largely through the verbal and written efforts of Pauling, they seemed plausible and helpful, the powerful experiments and calculations now available show those efforts and concepts to lack a firm foundation. Their continued promulgation is counterproductive to a profound understanding and communication of chemical knowledge. In this essay we discuss the origin and amplification of various ideas and terms that are common in textbooks of chemistry and in the lessons of instructors of chemistry but that are no longer acceptable as scientific truth.A pesar de que el enlace químico es ficción, conveniente y casi inofensivo, juega un enorme rol en el pensamiento y específicamente en la educación de químicos de todos los niveles. Mucha más ficción se ha dado durante los últimos 85 años. Aunque las ideas acerca de enlaces, orbitales, hibridación y tópicos relacionados fueron originadas y llegaron a ser ampliamente conocidas y de momento parecieron creíbles y benéficas, en gran parte por los esfuerzos de palabra y escritos de Pauling, los experimentos y cálculos disponibles actualmente muestran que dichos esfuerzos y conceptos carecen de bases firmes. La continua promulgación de ellos es contraproducente a un entendimiento profundo y a la comunicación de conocimiento químico. En este ensayo se discute el origen y la amplificación de varias ideas y términos que son comunes en textos de química y en las clases de profesores de química, pero que no son aceptados actualmente como una verdad científica

The legacy of van der Waals

The physical implications of the form and nature of the van der Waals equation of state are explained. The relation of this equation to so-­‐‐called van der Waals forces and radii is discussed. The conclusion is drawn that the van der Waals equation of state is practically worthless and its use should be abandoned. *** Resumen Se explican las implicaciones físicas de la forma y la naturaleza de la ecuación de estado de van der Waals. Además, se discute la relación entre esta ecuación y las llamadas fuerzas y radios van der Waals. Se llega a la conclusión de que la ecuación de estado de van der Waals no es útil y que no debería utilizarse.Se explican las implicaciones físicas de la forma y la naturaleza de la ecuación de estado de van der Waals. Además, se discute la relación entre esta ecuación y las llamadas fuerzas y radios van der Waals. Se llega a la conclusión de que la ecuación de estado de van der Waals no es útil y que no debería utilizarse

Graph Theory and simple Hueckel Theory applied to benzene

We compare the results of application of graph theory and of simple Hueckel theory in its traditional form to benzene, as an instance of a conjugated molecular system. The identity of the results of solution of eigenvalues of the vertex adjacency matrix and characteristic values of the Hueckel determinant prove the isomorphism of these two formalisms. Because of the gross deficiencies of the Hueckel theory, we advocate its elimination from the teaching of chemistry in favour of graph theory that has many applications to molecular topology.Se compararon los resultados de la aplicación de la teoría de gráficos y de la teoría de Hueckel tradicional a benceno, como ejemplo de un sistema molecular conjugado. Los resultados idénticos entre los eigenvalores de la matriz de adyacencia de los vértices y los valores característicos del determinante de Hueckel verifican el isomorfismo de los dos formalismos. Se recomienda la eliminación de la teoría de Hueckel por sus deficiencias y en su lugar utilizar la teoría de gráficos que tiene muchas aplicaciones en topología molecular

Measurement of single electrons and implications for charm production in Au+Au collisions at root(NN)-N-S=130 GeV

Transverse momentum spectra of electrons from Au+Au collisions at roots(NN) = 130 GeV have been measured at midrapidity by the PHENIX experiment at the Relativistic Heavy Ion Collider. The spectra show an excess above the background from photon conversions and light hadron decays. The electron signal is consistent with that expected from semileptonic decays of charm. The yield of the electron signal dN(e)/dy for p(T) \u3e 0.8 GeV/c is 0.025 +/- 0.004(stat) +/- 0.010( syst) in central collisions, and the corresponding charm cross section is 380 +/- 60(stat) +/- 200(syst ) mu b per binary nucleon-nucleon collision

Suppression of hadrons with large transverse momentum in central Au+Au collisions at root s(NN)=130 GeV

Transverse momentum spectra for charged hadrons and for neutral pions in the range 1 Gev/c \u3c P - T \u3c 5 GeV/c have been measured by the PHENIX experiment at RHIC in Au + Au collisions at root S(NN) = 130 GeV. At high p(T) the spectra from peripheral nuclear collisions are consistent with scaling the spectra from p + p collisions by the average number of binary nucleon-nucleon collisions. The spectra from central collisions are significantly suppressed when compared to the binary-scaled p + p expectation, and also when compared to similarly binary-scaled peripheral collisions, indicating a novel nuclear-medium effect in central nuclear collisions at RHIC energies

Centrality dependence of pi(+/-), K-+/-, p, and (p)over-bar production from root(NN)-N-S = 130 GeV Au+Au collisions at RHIC

Identified pi(+/-), K+/-, p, and (p) over bar transverse momentum spectra at midrapidity in root s(NN) = 130 GeV Au + Au collisions were measured by the PHENIX experiment at RHIC as a function of collision centrality. Average transverse momenta increase with the number of participating nucleons in a similar way for all particle species. Within errors, all midrapidity particle yields per participant are found to be increasing with the number of participating nucleons. There is an indication that K+/-, p, and (p) over bar yields per participant increase faster than the pi(+/-) yields. In central collisions at high transverse momenta (p(T) greater than or similar to 2 GeV/c), (p) over bar and p yields are comparable to the pi(+/-) yields

Net charge fluctuations in Au+Au interactions root s(NN)=130 GeV

Data from Au+Au interactions at s(NN)=130 GeV, obtained with the PHENIX detector at the Relativistic Heavy-Ion Collider, are used to investigate local net charge fluctuations among particles produced near midrapidity. According to recent suggestions, such fluctuations may carry information from the quark-gluon plasma. This analysis shows that the fluctuations are dominated by a stochastic distribution of particles, but are also sensitive to other effects, like global charge conservation and resonance decays

Event-by-event fluctuations in mean p(T) and mean e(T) in root s(NN)=130 GeV Au+Au collisions

Distributions of event-by-event fluctuations of the mean transverse momentum and mean transverse energy near mid-rapidity have been measured in Au+Au collisions at roots(NN)=130 GeV at the Relativistic Heavy-Ion Collider. By comparing the distributions to what is expected for statistically independent particle emission, the magnitude of nonstatistical fluctuations in mean transverse momentum is determined to be consistent with zero. Also, no significant nonrandom fluctuations in mean transverse energy are observed. By constructing a fluctuation model with two event classes that preserve the mean and variance of the semi-inclusive p(T) or e(T) spectra, we exclude a region of fluctuations in root s(NN)=130 GeV Au+Au collisions

Transverse-mass dependence of two-pion correlations in Au+Au collisions at root(NN)-N-S=130 GeV

Two-pion correlations in roots(NN) = 130 GeV Au+Au collisions at RHIC have been measured over a broad range of pair transverse momentum k(T) by the PHENIX experiment at RHIC. The k(T) dependent transverse radii are similar to results from heavy-ion collisions at roots(NN) = 4.1 , 4.9, and 17.3 GeV, whereas the longitudinal radius increases monotonically with beam energy. The ratio of the outwards to sidewards transverse radii (R-out/R-side) is consistent with unity and independent of k(T)