Mercury electron affinity

Table 18.2 Occupation probability of the valence orbital of a few alkali and halide ions adsorbed on mercury ( = 4.5 eV). For alkali atoms eo denotes the ionization energy for halide atoms, the electron affinity.

According to the data in Figure 6.6, zinc, cadmium, and mercury all have near-zero electron affinities. Explain. 

Another clear example is the effect of methyl groups on B-subgroup metals. Table 11 compares stability data for mercury, thallium, and lead systems. There is now an effective reduction of (b)-class character due to the extra ligands CH3- This must be attributed to the lowered electron affinity of the metal orbitals if our discussion is correct. 

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. 

Many years ago, geochemists recognized that whereas some metallic elements are found as sulfides in the Earth s crust, others are usually encountered as oxides, chlorides, or carbonates. Copper, lead, and mercury are most often found as sulfide ores Na and K are found as their chloride salts Mg and Ca exist as carbonates and Al, Ti, and Fe are all found as oxides. Today chemists understand the causes of this differentiation among metal compounds. The underlying principle is how tightly an atom binds its valence electrons. The strength with which an atom holds its valence electrons also determines the ability of that atom to act as a Lewis base, so we can use the Lewis acid-base model to describe many affinities that exist among elements. This notion not only explains the natural distribution of minerals, but also can be used to predict patterns of chemical reactivity. 

Certain negative ions such as Cl , Br, CNS , N03 and SO2 show an adsorption affinity to the mercury surface so in case (a), where the overall potential of the dme is zero, the anions transfer the electrons from the Hg surface towards the inside of the drop, so that the resulting positive charges along the surface will form an electric double layer with the anions adsorbed from the solution. Because according to Coulomb s law similar charges repel one another, a repulsive force results that counteracts the Hg surface tension, so that the apparent crHg value is lowered. 

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