Silver covalent radius

Lanthanide contraction has important consequences for the chemistry of the third-row transition metals. The reduction in radius caused by the poor shielding ability of the 4f electrons means that the third-row transition metals are approximately the same size as their second-row congeners, and consequently exhibit similar chemical behavior. For instance, it has been shown that the covalent radius of gold (125 pm) is less than that of silver (133 pm). 

In addition to the nitrate, sulfate, acetate, and halides of silver, all of which are familiar, the subfluoride, Ag2F, should be mentioned. This unusual compound, prepared by the reaction of the ordinary fluoride with silver metal, may be considered to contain alternate Ag and F ions, for the Ag—Ag distance has been found to be almost exactly twice the covalent radius of silver and the Ag—F distance about the same as that in silver fluoride. As might be expected (considering the odd number of electrons in the AgJ ion), the compound is colored (it has a bronzelike lustre). Pauling described this substance picturesquely as being intermediate in character between a salt and a metal. ... 

Like copper, silver and gold have a single s electron outside the completed d shell, but in spite of the similarity in electronic structures and ionization potential, the chemistries of Ag, Au, and Cu differ more than might be expected. There are no simple explanations for many of the differences although some of the differences between Ag and Au may be traced to relativistic effects on the 6s electrons of the latter. The covalent radii of the triad follow the trend Cu < Ag Au, i.e., gold has about the same or a slightly smaller covalent radius than silver in comparable compounds, a phenomenon frequently referred to as relativistic contraction (c/. lanthanide contraction). 

The internuclear distance in the crystal, Roj is 2.88 A., and the covalent radius sum Rc is 2.48. The Ag—Ag bond energy has been estimated, from data for all the silver halides, to be about 19 kcal. per mole. The dissociation energy of Br2 is 46.1 kcal. per mole, from which the geometric mean for AgBr is found to be 29.5. The six bonds that must be broken for atomization, per formula unit, of this rock salt structure utilize only four electron pairs, from which n = 4. The covalent contribution is ... 

Other Covalent Radii. In Cu20 and Ag20 each metal atom is equidistant from two nearest oxygen atoms, the interatomic distances corresponding to the radius values 1.18 and 1.39 A for Cu1 and Agl with coordination number two. In KAg(GN)2, in which each silver atom is similarly attached to two cyanide groups1), the effective radius of Agl is 1.36 A. It has been pointed out to us by Dr. Hoard that the work of Braekken2) indicates the presence of strings —Ag—G=N—Ag—G... 

Numerical data are much more interesting—and lead to deeper understanding—when we can find patterns in the numbers. When we examine the data in Table 8.8, we see that the transfer of an ion from the gas phase into water is more exothermic the greater the charge of the ion and the smaller its radius. There are exceptions Ag+ is bigger than Na+, but its hydration is more exothermic. The explanation of this anomaly may be that the Ag+ ion can form covalent bonds with the hydrating water molecules. The low solubility of silver salts supports this explanation. 

Between silver in period 5 (atomic number 47) and gold in period 6 (atomic number 79) 32 electrons have been added, 14 of them in the 4f subshell. The number of positive protons in the nucleus has, of course, also increased by 32. Electrons in an f subshell are, however, not very effective in screening outer-shell electrons from the nucleus. As a result the outer-shell electrons are held tightly by the nucleus. If we go from an atom with 47 electrons (Ag) to one with 79 (Au) an increased atomic radius would be expected. Surprisingly, this is not the case. The covalent radii are 1.5 A for silver and 1.44 A for gold. As a consequence, the outer electrons are strongly attracted by the nucleus and the tendency to form ions is extremely small. 

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