Trivalent terms Links

The term valence, of which ambivalence is not merely a variation, but a decidedly new and separate concept, derives from chemistry and atomic physics. Valence can refer to an extract or tincture, usually from an herb. In this connotation, it has obvious ties with the field of medical alchemy, or iatrochemistry. In the mid-i8oos, valence theory began to be used to signify the normal number of bonds that a given atom can form with other atoms—a register that links valence with philosophical materialism, matter, and Epicurianism. In recent scientific work, valence refers specifically to the number of electrons in the outermost shell of atoms. It is not provisional or occasional in its relation to the atom. Valence is atomicity. It defines a given chemical element, perhaps not in its essence, but in its capacity to combine with other elements—its potentiality. Valence is denoted by a simple number, and elements are said to be monovalent, bivalent, trivalent, quadrivalent, and so on. About one-fifth of all elements have a fixed valence (sodium is always i, or monovalent calcium is always 2, or bivalent and so on). Many elements have valences that are variable, depending on the other elements with which they are combined. 

The first research on these compounds was carried out by Claus,2 who described two classes of ammino-derivatives obtained from ruthenium diehloride, namely, those obtained from tlie hydroxide, Ru(NH3)4(OH)2, and those from the hydroxide of composition Ru(NH3)2(OH)2. These compounds were examined later by Jolv,3 who showed that they contained, besides ammonia and hydroxyl group, a nitroso-group linked to ruthenium, giving rise to the trivalent group (RuNO). He termed them ruthenium nitroso-ammonium compounds. These containing two molecules of ammonia were represented by the formula Ru(NH3)2NO(OH)3.H20, and those containing four molecules of ammonia in the molecule by the formula Ru(NH3)4NO.OH.R2 (where R represents a monovalent acidic radicle). 

I argued in chapter 2 that Wurtz s choice of the terms "triatomic," "polyatomic," and "atomicity" (Atomigkeit) (for what chemists later called trivalent, polyvalent, and valence) may have directly reflected his subatomic speculation, which pictured (e.g.) the "triatomic" nitrogen atom as an indissoluble accretion of three subatoms, each exerting one unit of valence that constitutes the ability to link with an affinity unit of another atom. I suggested further that this visual model may have formed the basis for Kekule s omnibus vision and for his theory of "atomicity of the elements." His choice of the term "affinity units" for what we now call valences is another indication that this was how he was thinking. 

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