ELECTRONEGATIVITY AND STRENGTH OF ACIDS AND BASES IN AQUEOUS SOLUTIONS

Abstract

Сoncepts of acidity-basicity for systems of different types are considered. The application of the parameter of effective electronegativity for estimating the acidity is proposed, the value of which is calculated from the thermochemical data of acid-base reactions in the condensed state (liquid, solid). The basis is the value of electronegativity of SO3, which should be equal to 3.00. Its values are in the range of 2.0 ÷ 3.1 for acid oxides and 0.3 ÷ 1.6 for oxides of basic nature. A significant group consists of oxides of bifunctional nature (amphoteric oxides) whose electronegativity values are 1.7 ÷ 1.9. A characteristic feature of amphoteric oxides is the manifestation of two values of electronegativity, corresponding to acid and basic functions. It is shown that the behavior of water as a characteristic amphoteric oxide is similar. Some predominance of acidic properties of water over the basic ones is shown and the possible reason for such behavior is discussed. To take into account this phenomenon, a method of converting the electronegativity of water to its value for the oxide partner during hydration is proposed. The values of electronegativity of hydroxides of elements (acidic, basic and amphoteric) were carried out by averaging them for components on the principle of additivity, the correctness of which is confirmed by direct calculations for individual hydroxides. It is shown that in the formation of hydroxides of elements there is a convergence between the values of electronegativities of acidic and basic oxides, ie the reduction of the former and the growth of the latter. Instead, in the case of amphoteric hydroxides, no noticeable changes in electronegativities compared to the original oxides occur. There is a qualitative correlation between the electronegativity of the hydroxides of the elements and the acidity (basicity) constants of their aqueous solutions, which is a reflection of their strength. This allows predicting the strength of acids and bases based on the electronegativity of hydroxides.