Definition and types of Oxides in chemistry

 Oxides are chemical compounds containing one or more oxygen atoms and another element combine together. Binary compounds are compounds containing two elements only. Oxides in general are binary compounds of metals or non-metals with oxygen, e.g. MgO, SO₂. 

The word binary is derived from the Greek prefix Bi meaning two. Binary compounds of oxygen are generally classified into four groups: 

1.  Acidic oxides
2. Basic oxides
3. amphoteric oxides
4. neutral oxides
5. neutral oxides

Acidic oxides

Acidic oxides are oxides formed between a non-metal and oxygen. They are oxides of non-metals which dissolve in water to form acids and react with alkalis to form salt and water only.

Let consider a situation where powdered carbon is heated over a Bunsen burner until red-hot, then plunged into a jar of oxygen. It glows bright red, and the gas carbon dioxide is formed according to the equation below:

C_(s) + O_2(g) → CO_2(g)

Another situation involves sulfur catching fire over a Bunsen burner, and burns with a blue flame. In pure oxygen it burns even brighter. The gas sulfur dioxide is formed according to the equation below:

S_(s) + O_2(g) → SO_2(g)

Carbon dioxide is slightly soluble in water. The solution will turn litmus red: it is acidic. The weak acid carbonic acid has formed. Sulfur dioxide  also dissolve in water to form acids. So they are all called acidic oxides. Acidic oxides in general combine with water to produce an acids, e.g.

CO_2(S) + H₂O_(l) → H₂CO_3(aq)

SO_2(S) + H₂O_(l) → H₂SO_3(aq)

In general, non-metals react with oxygen to form acidic oxides.

Basic  Oxides

A basic oxide is an oxide formed between a metal and oxygen.

Let likewise consider two situations. First will be that in which a magnesium ribbon is lit over a Bunsen flame, and plunged into a jar of oxygen. It burns with a brilliant white flame, leaving a white ash, magnesium oxide:

2Mg_(S) + O_2(g) → 2MgO_(s)

Second: Hot iron wool is plunged into a gas jar of oxygen. It glows bright orange, and throws out a shower of sparks. A black solid is left in the gas jar. It is iron(III) oxide:

4Fe_(S) + 3O_2(g) → 2Fe₂O₃

Ferric oxide is an example of iron(III)oxide occurring as rust or haematite

Basic oxides have two significant properties.

1.  Basic oxides react with acids to form a salt and water only.

CaO_(S) + 2HCl_(g) →CaCl₂ +  H₂O_(l)

MgO_(S) + 2HCl_(g) →MgCl₂ +  H₂O_(l)

2. If a basic oxide is soluble in water, it forms an alkaline solution.

CaO_(S) + H₂O_(l) → Ca(OH)_2(aq)

In general, metals react with oxygen to form basic oxides. Basic oxides belong to the larger group of compounds called bases.

Amphoteric oxides

An amphoteric oxide is an oxide of a metal which exhibit both basic and acidic characteristics. An amphoteric oxides shows two different types of reaction: basic and acidic.

An amphoteric oxide reacts with an acid to produce salt and water only, i.e. it behaves like a basic oxide and exhibit basic properties. E.g.

ZnO_(S) + H₂SO₄ → ZnSO₄ +  H₂O_(l)

An amphoteric oxide also react with an alkali solution to produce salt, i.e. it behaves like an acidic oxide and exhibit acidic properties.

ZnO_(S) + 2NaOH +  H₂O_(l) → Na₂Zn(OH)_4(aq)

An amphoteric oxide will react with both acids and alkalis

Neutral oxides

Some oxides of non-metals are neither acidic nor basic: they are neutral. Neutral oxides are oxides which shows neither basic nor acidic properties. The gases carbon(II)oxide (CO) and dinitrogen oxide,  (N₂O) are examples of neutral oxides. (Other nitrogen oxides are acidic.)