Acid-base behavior, of element

One may approach the acid-base behavior of elements in water from a different angle. 

The pattern of oxidation states correlates with the pattern of acid-base behavior of d-metal oxides. Although most d-metal oxides are basic, the oxides of a given element show a shift toward acidic character with increasing oxidation number, just as the oxoacids do (recall Section 10.10). The family of chromium oxides is a good... 

These atomic properties have a profound effect on many macroscopic properties, including metallic behavior, acid-base behavior of oxides, ionic behavior, and magnetic behavior of the elements and their compounds. 

Acid-Base Behavior of the Element Oxides Metals are also distinguished from nonmetals by the acid-base behavior of their oxides in water ... 

Figure 8.17 The trend in acid-base behavior of eiement oxides. The trend in acid-base behavior for some common oxides of Group 5A(15) and Period 3 elements is shown as a gradation in color (red = acidic blue = basic). Note that the metals form basic oxides and the non-metals form acidic oxides. Aluminum forms an oxide (purple) that can act as an acid or as a base. Thus, as atomic size increases, ionization energy decreases, and oxide basicity increases.

Remember, though, that some elements don t lit these categories as graphite, non-metallic carbon is a good electrical conductor the nonmetal iodine is shiny metallic gallium melts in your hand mercury is a liquid and iron is brittle. Despite such exceptions, in this discussion, we U make several generalizations about metallic behavior and its application to the acid-base behavior of oxides. 

Figure 8.16 Acid-base behavior of some element oxides.

In Figure 8.16, the acid-base behavior of some common oxides of elements in Group 5A(15) and Period 3 is shown with a gradient from blue (basic) to red (acidic) ... 

With the exception of OF2, the oxides of the elements in groups 14 to 17 react with water to give oxoacids, as shown above for SO3. OF2 reacts with water, but the reaction gives a binary acid (HF) and not the oxoacid (HOF). That the acid-base behavior of OF2 is different from the oxides of other p-block elements comes as no surprise OF2 is not an oxide. It is a fluoride with oxygen having an oxidation state of +2. 

Both our original prediction about the effect of ionization energy on acid-base behavior and the trend which we have observed in the first three elements lead us to expect that the hydroxide or oxide of silicon should not be basic, but perhaps should be weakly acidic. This is in fact observed. Silicon dioxide, Si02, can exist as a hydrated solid containing variable amounts of water,... 

The ionic-potential (Ip) concept discussed in Chap. 3 best describes element behavior at intermediate pH s. Most of the metal oxides and hydroxide minerals formed by cations with Ip values between about 3 and 8.2 become significantly soluble in acid waters, where the high H+ concentrations can break metal-0 or metal-OH bonds to form water and release metal cations to solution. Some of these otherwise insoluble metal oxides and hydroxides (for example, those of Al and Fe " ) are also solubilized by high pH s. In other words, the mobilities of these metal cations depend on the acid-base properties of the water, as well as on their ionic potentials. The rate of chemical weathering is also greatly accelerated in strongly acid waters. 

SECTION 17.7 Metallic elements vary a great deal in the solubilities of their salts, in their acid-base behavior, and in their tendencies to form complex ions. These differences can be used to separate and detect the presence of metal ions in mixtures. Qualitative analysis determines the presence or absence of species in a sample, whereas quantitative analysis determines how much of each species is present. The qualitative analysis of metal ions in solution can be carried out by separating the ions into groups on the basis of precipitation reactions and then analyzing each group for individual metal ions. 

Consistent with the position of the metal-nonmetal line (and the corresponding acid-base character of metal and nonmetal oxides), boron oxide is an acid anhydride, whereas the oxides of the heavier elements progress from amphoteric to basic in behavior. Boron oxide, then, reacts with water, as shown in Equation (14.2), to produce boric acid, B(OH)3 or H3BO3 ... 

As we have seen, the Lewis theory of acid-base interactions based on electron pair donation and acceptance applies to many types of species. As a result, the electronic theory of acids and bases pervades the whole of chemistry. Because the formation of metal complexes represents one type of Lewis acid-base interaction, it was in that area that evidence of the principle that species of similar electronic character interact best was first noted. As early as the 1950s, Ahrland, Chatt, and Davies had classified metals as belonging to class A if they formed more stable complexes with the first element in the periodic group or to class B if they formed more stable complexes with the heavier elements in that group. This means that metals are classified as A or B based on the electronic character of the donor atom they prefer to bond to. The donor strength of the ligands is determined by the stability of the complexes they form with metals. This behavior is summarized in the following table. 

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