Chemical Properties of Period 3 Oxides

Tracing the shift from Basic (Ionic) to Acidic (Covalent) character.

Element	Formula	Bonding	Nature	Reaction w/ Water	pH
Na	\(Na_2O\)	Ionic	Basic	\(Na_2O + H_2O \to 2NaOH\)	~14
Mg	\(MgO\)	Ionic	Basic	\(MgO + H_2O \to Mg(OH)_2\)	~9
Al	\(Al_2O_3\)	Ionic*	Amphoteric	Insoluble	—
Si	\(SiO_2\)	Giant Cov.	Acidic	Insoluble	—
P	\(P_4O_{10}\)	Molecular	Acidic	\(P_4O_{10} + 6H_2O \to 4H_3PO_4\)	~2
S	\(SO_3\)	Molecular	Acidic	\(SO_3 + H_2O \to H_2SO_4\)	~1

The Special Case: Aluminum Oxide

Aluminum oxide is amphoteric, meaning it can react as both an acid and a base.

Reacts with warm, dilute acid:

\(Al_2O_3 + 6HCl \to 2AlCl_3 + 3H_2O\)

Reacts with hot, concentrated alkali:

\(Al_2O_3 + 2NaOH + 3H_2O \to 2NaAl(OH)_4\)

(Sodium Aluminate)