Oxides Group IIIA elements

In this chapter, a brief summary of studies that made use of calorimetry to characterize compounds comprising group IIIA elements (zeolites, nitrides, and oxides catalysts) was presented. It was demonstrated that adsorption microcalorimetry can be used as an efficient technique to characterize the acid-base strength of different types of materials and to provide information consistent with the catalytic data. 

Corresponding to the place in the Periodic Table, in Tl-compounds the metal occurs in oxidation states + I and + III. In contrast to the other Group IIIA elements, the monovalent form is more stable than the trivalent. The chemical and physical properties of metallic thallium and thallium compounds are similar to those of adjacent elements, mainly to lead (atomic number 82). 

Catalyst based on an intimate mixture of Pr and group IIIA elements and optional zirconium oxides. 

The Group IIIA elements consist of boron, aluminum, gallium, indium, and thallium. They have a valence shell configuration of ns r

[Pg.54]

Boron is a Group IIIA element (+3 ion), but rarely occurs as a trivalent ion in nature. Its propensity to bind with oxygen results in primarily oxide and hydroxide compounds. Boron occurs as boric acid (B(OH)3) in low pH... 

There is also a pronounced tendency for the Group IIIA metals to form metal-metal bonds and bridged structures. The electron configuration ns2 np1 suggests the possible loss of one electron from the valence shell to leave the ns2 pair intact. The electron pair that remains in the valence shell is sometimes referred to as an inert pair, and a stable oxidation state that is less than the group number by two units is known as an inert pair effect. The fact that oxidation states of +2, +3, +4, and +5 occur for the elements in Groups IVA, VA, VIA, VIIA, respectively, shows that the effect is quite common. Thus, it will be seen that the Group IIIA metals other than aluminum have a tendency to form +1 compounds, especially thallium. 

Note The only thing we can definitely conclude about X is that it has an oxidation state of +3. Element X is not necessarily in group IIIA, although it does not hurt in this particular problem to make that assumption. That could mean X was a transition metal or even a nonmetal with that oxidation state. 

The ionic potentials of the nonmetal elements in Groups IIIA to VIA exceed 100 nm for their common oxidation states, and therefore these elements form oxyanions instead of hydrolytic species in soil solutions. The same tendency is observed for the Group VIB metals chromium and molybdenum. Examples of inorganic oxyanions commonly found in the aqueous phases of soil are B(OH)J, CO, NOJ, H3Si04, POj", SOj", AsOl", SeOf", MoOl , and, when the oxyanion is multivalent, some of the protonated forms. The qualitative and mechanistic features of the adsorption of these oxyanions—a topic on which there is an abundant literature —are the principal concerns of the present section. Quantitative models of inorganic oxyanion adsorption are described in Chap. 5. 

Oxide formation can be a very troublesome interference, especially with group IIA and IIIA elements, since oxides of these elements are thermally very stable. Two approaches to minimizing this type of interference are available. 

Elements of Group IIIA have oxidation numbers of +3. 

---