Oxides-Classification And Periodic Trends Of Oxides

Learning objectives

In this article, the author has explained what are oxides, the types and classification of oxides, and variation in the periodic table.

Oxides

Table of Contents

Binary compounds of oxygen with elements of the periodic table are called oxides.
Definition of oxides

Examples of oxides

Na₂O, CaO, Al₂O₃, CO₂, NO₂, Cl₂O₃, OF₂ etc are all oxides.

Types of oxides

There are three types of oxides on the basis of acidic properties.

Basic oxides
Acidic oxides
Amphoteric oxides

Basic oxides

Those oxides which yield bases in water and are mostly made up of metal oxides are known as basic oxides.
Definition of basic oxides

The elements of group I-A and II-A groups except Be and the elements of the II-A group except Zn from basic oxides.

Whenever they are dissolved in water, these give bases. With the increases in metallic character of the elements down the group the oxides of the elements of the same group become more and more basic. CO₂and SiO₂ are acidic oxides. GeO₂ and SnO₂ are amphoteric oxides while PbO₂ is basic oxides.

Acidic oxides

Those oxides which when dissolved in water give the acidic solution are known as acidic oxides.
Definition of acidic oxides

Oxides of carbon, nitrogen and sulphur are acidic in nature. CO₂, NO₂, SO₂ are acidic oxides.

Amphoteric oxides

Those oxides which have acidic and basic character both are called amphoteric oxides.
Definition of amphoteric oxides

Amohoteric oxides behave as acids towards a strong base. They act bases towards a strong acid.

For example:

ZnO reacts with H+ ions to give Zn⁺² ion and behaves as a basic oxide.

ZnO also reacts with OH^– ions

Variation of the nature of oxides in the periodic table

There is an almost systematic variation of the acidic and basic character of the oxides in groups and periods in the periodic table.

Following table gives the idea about classification of the oxides on the basis of acid base character.

Classification of oxides on the bases of acid base character

Variation of nature of oxides in a period

When we move from left to right in a period, the oxides become more and mmore acidic in nature. Look at the gradual increase of change in the nature of the oxides of third period.

Group	I-A	II-A	III-A	IV-A	V-A	VI-A	VII-A
Oxides	Na₂O	MgO	Al₂O₃	SiO₂	P₂O₅	SO₃	Cl₂O₇
Nature	Strongly basic	Basic	Amphoteric	Acidic	More acidic	Even more acidic	Strongly acidic

Variation of nature of oxides in a group

When we move from top to downward direction in a group; an increase in basic character oxides is observed. Look at the oxides of II-A group elements. BeO is least basic, while BaO has maximum basic character.

Group II-A

Oxidation state of the metal and its effect on the nature of oxides

There are certain metals that have variable oxidation states. Therefore, these metal gives various oxides. This can be explained by saying; greater the oxidation number of the metal, the greater the acidic character of the oxides.

Let us look at the oxides of Manganese (Mn)

Oxides of Manganese (Mn)

Acidic character of Oxides of Manganese in group

Oxides of nitrogen

These are five oxides of nitrogen and their acidic strengths increase with the increasing oxidation state of nitrogen.

Oxides of Sulphur

Similarly, the oxides of Sulphur have the same trends as above.