GROUP 13: ALUMINUM TO THALLIUM
The substance aluminum, indium, gallium and thallium have valence electron configurations (ns)2(np)1 and for the lighter elements their chemistry is dominated by the +3 oxidation state. The group trends are very different from those in groups 2 and 1. The Al3+ ion has a large radius ratio and is rigidly polarizing, so that significant deviations from simple ionic behavior are usually observed. The filling of the d shells (and 4f in period 6) goes to decreased electropositive character for Tl and Ga, In similar to that shown in group 12. There is also a progressive stabilization of lower oxidation states in lower side of the group.
Aluminum is common metallic element in the Earth's crust, being a constituent of almost all silicate minerals. Weathering leaves deposits of the very insoluble aluminum minerals Al(OH)3 and AlO(OH), known together as bauxite, which forms the principal source of the element. The metal is produce by electrolysis of fused cryolite Na3[AlF6]. Although reactive when clean, the metal easily builds a very resistant oxide film, which performs widespread applications as a lightweight construction material and in other vessels and cooking.
In, Ga and Tl are much less common substance, collect in small amounts from sulfide minerals of other elements and used only in specialized applications. The metals are less performing than aluminum in which the much bigger negative slope (negative electrode potential of Al is apparent. Thallium elements are extremely toxic but do not usually pose an environmental hazard because they are little used.