Jöns Jacob Berzelius

Electrochemical Theory

In many carefully made experiments, Volta has observed that two metals put in contact become electric, and that this is the cause of the phenomena of the electric pile. Davy later showed that this electrical state increases due to the force of mutual affinities of the bodies used, and that this effect can be produced, and even seen, by means of certain precautions, in all bodies which have affinity for each other. It also follows from the experiments of Davy that temperature, which, as we know, increases affinity, also increases the intensity of the electrical state in bodies which are in contact, but that this mechanical contact being followed by combination, all signs of electricity immediately cease, that is to say, at the instant when, in favorable circumstances, they burst into flame, the electrical division, or the charge which could be perceived, disappears. These facts agree well with the conjecture that the opposite electricities in the bodies which combine, mutually neutralize each other at the moment of combination, and then the fire is produced in the same manner as in the electric discharge.

But if these bodies, which are united and have ceased to be electric, should again be separated, and their elements restored to the isolated state with their original properties, they must recover the electrical state destroyed by the combination, or indeed, in other terms, if these combined bodies are restored for any reason to their original electrical state, which had vanished at their union, they must separate, and reappear with their original properties. Hisinger and I have observed that when the electric pile exerts its action on a conducting liquid, the elements of this liquid separate, oxygen and the acids are repelled from the negative pole toward the positive, and the combustible bodies as well as the salifiable bases from the positive pole toward the negative.

We believe we now know with certitude that bodies which are likely to combine show free, opposite electricities which increase in force as they approach the temperature at which combination occurs, until, at the instant of union, the electricity disappears with an elevation of temperature which is often so great that they burst into flame. On the other hand, we have the same certainty that combined bodies exposed in a suitable form to the action of the electric fluid, produced by discharge of a pile, are separated and regain their original chemical and electrical properties at the same time that the electricity which acted on them disappears.

In the actual state of our knowledge, the most probable explanation of combustion and the ignition which results from it is then: that in all chemical combinations there is neutralization of opposing electricities, and that this neutralization produces fire in the same manner that it produces it in the discharge of the electric jar, the electric pile, and thunder, without being accompanied, in these latter phenomenon, by chemical combination. . . .

The experiments made on the mutual electrical relations of bodies have taught us that they can be divided into two classes: electropositive and electronegative. The simple bodies which belong to the first class, as well as their oxides, always take up positive electricity when they meet simple bodies or oxides belonging to the second class; and the oxides of the first class always behave with the oxides of the other like salifiable bases with acids.

It has been believed that the electrical series of combustible bodies differs from that of their oxides; but although the different degrees of oxidation of several bodies present exceptions, the electrical order of combustible bodies agrees in general with that of their oxides, in such a way that the strongest degrees of oxidation in the affinity of different radicals are like those between the radicals themselves.

In arranging the bodies in the order of their electrical nature, there is formed an electro-chemical system which, in my opinion, is more fit than any other to give an idea of chemistry. I will speak more of this later.

Oxygen is, of all bodies, the most electronegative. As it is never positive relative to any other, and as, according to all chemical phenomena known up to the present it is not probable that any element of our globe can be more electronegative, we recognize in it an absolute negative. Also, in the electrochemical system, it is the only body whose electrical relations are invariable. The others vary in this sense, that one body can be negative with respect to a second, and positive with respect to a third: for example, sulphur and arsenic are positive relative to oxygen and negative relative to metals. The radicals of fixed alkalis and alkaline earths are, on the contrary, the most electropositive bodies; but they differ somewhat in degree;

and at the positive extreme of the electrical series, there is no body as electropositive as oxygen is electronegative.

The applications of this theory axe illustrated by the following extract, taken from the French edition of Berzelius’s textbook, Paris, 1831, volume 4.

The electrochemical properties of oxidised substances depend almost always exclusively on the unipolarity of their electropositive element, that is to say, of their radical. The oxide is ordinarily electronegative with regard to other oxides when its radical is negative with regard to their radicals, and vice versa. For example, sulfuric acid is electronegative with respect to all metallic oxides for the reason that sulfur is negative in relation to all metals. The oxides of potassium and zinc are, on the contrary, electropositive with regard to all oxidized substances, to the radicals of which, potassium and zinc are positive. This fact, the cause of which we are unable to explain, rectifies an inexact idea on the principle of acidity which in the antiphlogistic theory has been thought to be oxygen. We find now that it resides in the radical of the acid and that oxygen plays such an indifferent role that it enters equally into the strongest salifying bases, that is to say, the electropositive oxides and in the strongest acids or electronegative oxides. Sometimes it happens, however, that a positive oxide acquires by higher oxidation less electropositive properties, approaching electronegative, as, for example, stannic oxide and the acids of manganese. But in the strongest bases, such as potash and soda, an addition of oxygen may well destroy the positive reaction without, nevertheless, producing a negative; it is thus that the strongly salifying bases form peroxides. . . .

If these electrochemical views are correct it follows that all chemical combination depends solely on two opposing forces, positive and negative electricity, and that thus each combination should be composed of two parts united by the effect of their electrochemical reaction, provided that there exists no third force. Whence it follows that each compound substance, regardless of the number of its constituent principles, may be divided into two parts, of which one is electrically positive and the other negative. Thus, for example, sulfate of soda is not composed of sulfur, oxygen and sodium, but of sulfuric acid and soda¹ which both may again be divided into two elements, one positive and the other negative. Similarly alum cannot be considered as directly composed of its elements but should be regarded as the product of the reaction of sulfate of aluminum, a negative element, and sulfate of potash, a positive element. In this manner the electrochemical view equally well justifies what I have already detailed on particular compounds of the first, second and third orders, etc.

¹ [A vestige of this theory remains in the custom of reporting analysis on an oxide basis.]