Classification Of Oxides

This topic educates with the classification of oxides based on the nature and property of compounds. Oxides are binary compounds formed by the reaction of oxygen with other elements. Oxygen is highly reactive in nature. They react with metals and non-metal to form oxides.

What are Oxides?

The classification of oxides is done into neutral, amphoteric and basic or acidic based on their acid-base characteristics.

  1. An acidic oxide is an oxide which when combined with water gives off an acid.
  2. A basic oxide is an oxide which when combined with water gives off a base.
  3. When a substance reacts chemically, both as a base or acid it termed as an amphoteric solution.
  4. Neutral Oxide is one which neither has an acidic characteristic or a basic one.

Metal Oxides have an oxidation number of -2 and generally comprise of an oxygen anion. The Earth’s crust is mostly made up of oxides that are solid. Oxide coatings can get formed over pure elements too, for instance, a foil made of aluminum gets covered by a thin skin of Al2O3, and this skin defends the rest of the foil from corrosion.

Classification Of Oxides

Depending upon nature and the properties exhibited by compounds, they are classified into

  • Acidic oxides
  • Basic oxides
  • Amphoteric oxides
  • Neutral oxides

Basic oxide:

Metals react with oxygen to give basic compounds of oxygen. These compounds are usually ionic in nature. Group 1, 2 and lanthanides form basic compounds of oxygen when they react with dioxygen. During the formation of these compounds, a large amount of energy is released. These compounds readily react with water except few exceptions.

Examples: M2O3, MO2, ThO2

Na2O + H2O → 2NaOH

Acidic oxide:

Non-metals react with oxygen to form acidic compounds of oxides which are held together by covalent bonds. These compounds can also be called as acid anhydrides. Acid anhydrides usually have a low melting and boiling point except for compounds like B2O3 and SiO2 which have high melting points and form giant molecules.

Examples: NO, CO2

SO3 + H2O → H2SO4

B2O3 + H2O → 2H3BO3

Amphoteric oxide:

Amphoteric oxides are compounds of oxygen which exhibits both acidic as well as basic characteristics. These oxides when reacting with acid undergoes a neutralization reaction to form water and salt. This exhibits the basic property of the compounds. Similarly reacts with the alkali to form salt and water, exhibiting acidic property. Example: aluminium oxide

Acidic characteristics:

AL2O3 + 6HCl → 2Al3+ + 6Cl– + 3H2O

Basic characteristics:

Al2O3 +2OH– + 3H2O → 2[Al (OH)4]–

Neutral Oxides:

Some compounds react with oxygen to form oxides which do not exhibit acidic nor basic characteristics. Such compounds are called as neutral compounds of oxygen.

Example: NO, CO.

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Practise This Question

Suboxides are a class of oxides wherein the electropositive element is in excess relative to the “normal” oxides - True or False?