Silver electron affinity

Bromine has a lower electron affinity and electrode potential than chlorine but is still a very reactive element. It combines violently with alkali metals and reacts spontaneously with phosphorus, arsenic and antimony. When heated it reacts with many other elements, including gold, but it does not attack platinum, and silver forms a protective film of silver bromide. Because of the strong oxidising properties, bromine, like fluorine and chlorine, tends to form compounds with the electropositive element in a high oxidation state. 

The Principle of Hard and Soft Acids and Bases states that hard acids form more stable complexes with hard bases and soft bases form more stable complexes with soft acids. In orbital terms hard molecules have a large gap between the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO), and soft molecules have a small HOMO-LUMO gap. In recent years it has been possible to correlate the hardness with the electronic properties of the atoms involved. Thus, if the enthalpy of ionisation (I) and the electron affinity (A) are known the so-called absolute hardness (t ) and absolute electronegativity (%) can be found from r = (I - A) / 2 and % = (I + A) / 2. For example, the first and second ionisation enthalpies of sodium are 5.14 and 47.29 eV. Thus for Na+, I = + 47.29 and A = + 5.14, so r = (47.29 - 5.14) / 2 = 21.1. Similarly for silver the first and second ionisation enthalpies are 7.58 and 21.49eV, so for Ag+ we have, n = (21.49 - 7.58) 12 = 6.9. 

The electron affinities of adsorbed silver clusters, calculated using Eq. (27), are shown in Table XI. These values indicate that electron-trapping ability of Ag and Ag3 is greater than that of AgBr with the reverse true for Ag2 and Ag4. With inareasing Ag cluster size, EA increases, as expected for isolated Ag clusters and shown in Fig. 7, so that at sufficient size, EA is greater for the cluster than the AgBr model. When this is true, electrons added to the crystal become localized at the Ag cluster where Ag+ reduction takes place. 

The MO calculations explain a possible route for silver cluster formation and catalysis in silver bromide. The electron affinity of the silver center determines... 

The chemistry of gold is more diversified than that of silver. Six oxidation states, from -I to III and V, occur in its chemistry. Gold(-I) and Auv have no counterparts in the chemistry of silver. Solvated electrons in liquid ammonia can reduce gold to give the Au" ion which is stable in liquid ammonia (E° = -2.15 V). In the series of binary compounds MAu (M = Na, K, Rb, Cs), the metallic character decreases from Na to Cs. CsAu is a semiconductor with the CsCl structure and is best described as an ionic compound, Cs+Au . The electron affinity of gold (—222.7 kJ mol"1) is comparable to that of iodine (-295.3 kJ mol-1). Gold in the oxidation state -I is also found in the oxides (M+ Au O2 (M = Rb, Cs) these, too, have semiconducting properties.1... 

The small affinities of lithium and sodium are of little importance, but copper, silver and gold, with completed d shells, possess marked electron affinity and whereas the alkaline earth metals, with completed s levels, have negative electron affinities, mercury, with a completed d and s level, has a high positive electron affinity. 

If we had assumed the simple ionic model here, the Born-Mayer equation would have given a lattice energy of 178.4 kcal. per mole. The ionization energy of silver is 176.2 and the electron affinity of bromine (2) is — 79.1, from which the atomization energy of AgBr is 81.3 kcal. per mole, in error by nearly 40 kcal. Efforts to modify the Born-Mayer equation to take other factors into account (5) have not produced satisfactory results for such compounds. 

The heavy metal pseudohtilides fall in this group since covalent forces are partially present. The structural parameters listed in Table 4 show that thallous azide, fulminate and cycmate are isostructural with the tetragonal alkali metal salts, while thallous thiocyanate is isostructural with the room temperature phase of potassium thiocyanate. The lattice constants of the salts axe all indicative of abnormally short metal-anion distances. The silver salts form an interesting series where the subtle interactions which result as a function of the electron affinity, electronic structure and size of the anions, stimulate somewhat predictable variations of crystal geometry. Silver azide is an example of a distortion of the tetragonal D4 (Fig. 1) lattice due to covalent metal-emion interaction which lowers the space symmetry of the crystal to D2 (29), while silver thiocyanate is mainly covalent with bidentate metal-anion chains... 

Let us calculate the electron affinity (EA) and ionization potential (IP) of clusters of silver species adsorbed to virtual sites near the defect. These levels are shown for the positive kink in Figure 3 relative to their positions in the valence and conduction bands of the model. The EA has a sawtooth behavior but is larger than the AgBr EA for neutral clusters of all sizes up to 8 atoms. Thus, electron trapping will occur at clusters on the positive kink. Corresponding data for the negative and double kink are shown in Figure 4. 

Figure 3. Electron affinity ( ) and ionization potential (-------) for silver clus-...

Current-potential curves of the O2 reduction were measured [68] in concentrated KOH on alloy electrodes prepared from silver and small amounts of elements that form oxides of low electron affinity. The reactivity of a silver — 1.7w/o (weight percent) magnesium alloy was better than that of pure silver. In contrast, no improvement was found for foils of silver — Iw/o thorium, silver — Iw/o radium, and silver — 1 w/o barium. 

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