Use the Lewis dot symbols to describe the formation of aluminium oxide `(Al_2O_3)`.
Strategy: The Lewis dot symbols of Al and O are
`:Al*" "*ddotunderset(..)O*`
Thus, the common valency of `Al` is 3 while that of O is two. As a result, aluminium tends to form the trivalent cation `(Al^(3+))` and oxygen, the divalent anion `(O^(2-))`. The transfer of electrons is from Al to O. There are three valence electrons in each Al atom, each O atom needs two electrons to form the `O^(2-)` ion, which is isoelectronic, with neon. Thus, the simplest neutralizing ratio of `Al^(3+)` to `O^(2-)` is `2:3`, two `Al^(3+)` ions have a total charge of `6+` and three `O^(2-)` ions have a total charge of `6-`. Thus, the empirical formula of aluminium oxide is `Al_2O_3`.