Valency

About: Valency is a research topic. Over the lifetime, 1632 publications have been published within this topic receiving 26141 citations.

Valency correlation diagrams

Abstract: The general criteria for a molecular orbital quantity to serve as a successful Walsh ordinate to give correct qualitative predictions of molecular shape are formulated.

Valency and molecular structure

Abstract: Valency is defined for each molecular orbital. The molecular orbital valency values are shown to be a good measure of the bonding nature of the molecular orbital. Comparisons are made with photoelectron spectral studies and Mulliken overlap population analysis. The variation of molecular valency and molecular orbital valency with bond angle is studied. It is found that for all the molecules presently considered, energy is linearly related to valency and that the molecular valency reaches a maximum at the equilibrium bond angle. It is also shown that the molecular orbital valency can serve as a quantitatively reliable ordinate for Mulliken-Walsh diagrams.

Oxides of Praseodymium

Abstract: THE two oxides of praseodymium described in the literature are the light green sesquioxide and the dark brown ‘air-ignited’ oxide. It is generally agreed that the composition of the latter approximates to Pr6O11. Prandtl and his school1 claim that praseodymium can exhibit a higher valency of 5, and on this basis designate the air-ignited oxide as 2Pr2O3.Pr2O5. Marsh2 affirms, however, that praseodymium possesses a maximum valency of 4, a conclusion which is well supported by the work of Zintl and Morawietz3, and represents Pr6O11 as the double oxide, 4PrO2.Pr2O3.

Temperature induced valence instabilities in ternary Eu-pnictides: a comprehensive view

Abstract: We report on measurements of the lattice constants, magnetic susceptibility, LIII X-ray absorption and Mossbauer-effect on EuNiP and EuPdP, which crystallize in the hexagonal layered Ni2In structure. In both compounds the Eu valence above 510 K is 2.33. With decreasing temperature they show one (EuPdP) or two (EuNiP) first order phase transitions with a valence increase of about 0.16. At the same time thec-axis shrinks while the a-axis even increases. From Mossbauer measurements we show that the nature of the valence mixing is static. In contrast, the valence mixing in isostructural EuPtP is static at low temperatures, too, but it becomes homogeneous valent above a first order phase transition at 235 K. The behaviour of these compounds (as well as that of EuPdAs) is explained in a new model of electrostatically charged layers. In this model we can explain the temperature dependence of the lattice constants, the static valence mixing and the occurrence of preferred valences of the order 2 6/n. Together with the compression shift model of Hirst we can also understand the mechanism of the phase transitions. A comparison with EuT2Si2 compounds in ThCr2Si2 structure shows that in EuTX compounds only the electronic structure of the transition elements is relevant for the occurrence of mixed valency.