Metal Oxides and Non-metal Oxides (3.1.5)

Another way to describe acids and bases is their ability to accept and donate a pair of electrons.

Lewis acids: Can accept an electron pair.

Lewis bases: Can donate an electron pair.

Many Metal oxides ( contains oxygen ) ( Forms other Hydroxides / Bases ) are Lewis Bases:

• Group 1 Oxides

  • $M_2O(s) + H_2O(l) \rightarrow 2MOH(aq)$

  General equation for reaction w/ water.

• Group 2 Oxides

  • $MO(s)+ H_2O(l) \rightarrow M(OH)_2(aq)$

Non-metallic oxides are Lewis Acids (Form other acids by accepting an electron pair from Oxygen in water) :

• $CO_2(g)+H_2O(l) \rightarrow H_2CO_3(aq)$

  • Carbon dioxide + Water --> Carbonic Acid

Note: Going across any period the oxides of the elements become less and less basic and more acidic.

• $Na_2O(s)$is a stronger base than $MgO(s)$ when reacting w/ water

• $SO_3(l)$ is stronger acid than $P_4O_{10}(s)$

Chemical species that behaves like both a Lewis Acid & a Lewis base is called amphoteric.

• $Al_2O_3(s)$is amphoteric because it can both donate and accept an electron.

  • Reacting w/ base, aluminum oxide acts as a Lewis Acid.

$Al_2O_3(s) + 2NaOH(aq) + 3H_2O(l) \rightarrow 2Na[Al(OH)_4](aq)$

Aluminum Oxide + Sodium Hydroxide --> Sodium Aluminate

• Reacting w/ acid, aluminum oxide as as a Lewis Base

$Al_2O_3(s) + 6HCl(aq) \rightarrow 2AlCl_3(aq) + 3H_2O(l)$

Aluminum Oxide + Hydrochloric Acid --> Aluminum Chloride

These are Neutralization Reactions.

Other reactions

• Metals + Water $\rightarrow$Metal Oxide + Water
• $M + H_2O \rightarrow MO + H_2O$