Beryllium diagonal relationship with aluminum

The oxides of metalloids and some of the less electropositive elements are amphoteric (react with both acids and bases). Aluminum oxide, for instance, reacts with acids and with alkalis (aqueous solutions of strong bases). The oxides reveal a strong diagonal relationship between beryllium and aluminum, because beryllium oxide is also amphoteric. 

The diagonal relationship between beryllium and aluminum, discussed previously in Chapter 21, is evident in Table 22.1. Both beryllium (in group 2) and aluminum (in group 13) form network covalent solids with fluorine. 

Aluminum and beryllium have a diagonal relationship. Compare the chemical equations for the reaction of aluminum with aqueous sodium hydroxide to that of beryllium with aqueous sodium hydroxide. 

The diagonal band of metalloids dividing the metals from the non-metals is one example of a diagonal relationship (Section B). So is the chemical similarity of lithium and magnesium and of beryllium and aluminum. For example, both lithium and magnesium react directly with nitrogen to form nitrides. Like aluminum, beryllium reacts with both acids and bases. We shall see many examples of this diagonal similarity when we look at the elements in detail (in Chapters 14 and 15). 

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