# Simple Oxides: Acidic Oxide, Basic Oxide, and Amphoteric Oxide (2022)

• Written By Sahana Soma Kodarkar

Simple Oxides: Have you ever considered how simple and complex an oxide can be? As chemistry students, we must investigate everything thoroughly. A simple oxide is one that carries more oxygen atoms than the metal’s typical valency allows. To learn more about simple oxides and their types, read the below article.

## Oxides

The majority of elements in the periodic table, both metals, and nonmetals, combine with oxygen to produce binary compounds. Oxides are binary compounds of metals and nonmetals with oxygen. The oxidation state of oxygen in these oxides is always $$-2$$.

Some elements (for example, $${\rm{Li}},{\rm{Mg}},{\rm{Al}},{\rm{Zn,}}$$ etc.) form only one oxide, whereas many others (for example, $${\rm{Fe}},{\rm{Cu}},{\rm{N}},{\rm{S}},{\rm{P}},$$ etc.) form multiple oxides. The nature of bonding in these oxides may be either ionic or covalent.Oxides can be simple (for example, $${\rm{MgO}},{\rm{A}}{{\rm{l}}_2}{{\rm{O}}_3},$$ etc.) or mixed (i.e., $${\rm{P}}{{\rm{b}}_3}{{\rm{O}}_4},{\rm{F}}{{\rm{e}}_3}{{\rm{O}}_4},$$ etc.).

## Types of Oxides

On the basis of oxygen content, the oxides can be classified into the following types:

I. Normal oxides: These oxides contain oxygen atoms as required in the oxidation state of $$–2$$. For example, $${\rm{N}}{{\rm{a}}_2}{\rm{O}},{{\rm{H}}_2}{\rm{O}},{\rm{MgO}},{\rm{A}}{{\rm{l}}_2}{{\rm{O}}_3},{\rm{C}}{{\rm{O}}_2},$$ etc.

II. Polyoxide: These oxides contain more oxygen atoms than the normal oxidation state of $$-2$$. These are the following two types:

a. Peroxide: In peroxides, two oxygen atoms are bonded to each other by one covalent bond, and each oxygen atom has an oxidation state of $$-1$$. In other words, all peroxides contain a peroxide ion $$\left( {{\rm{O}}_2^{2 – }} \right)$$ with the structure

For example, $${{\rm{H}}_2}{{\rm{O}}_2},{\rm{N}}{{\rm{a}}_2}{{\rm{O}}_2},{\rm{Ba}}{{\rm{O}}_2},$$ etc. Metallic peroxides, when treated with a dilute mineral acid, give hydrogen peroxide $$\left( {{{\rm{H}}_2}{{\rm{O}}_2}} \right)$$.
That is,

$${\rm{Ba}}{{\rm{O}}_2} + {{\rm{H}}_2}{\rm{S}}{{\rm{O}}_4} \to {\rm{BaS}}{{\rm{O}}_4} + {{\rm{H}}_2}{{\rm{O}}_2}$$

b. Dioxide: Oxides in which two oxygen atoms with $$-2$$ oxidation state combine with metal or nonmetal atoms. Dioxides do not form $${{\rm{H}}_2}{{\rm{O}}_2}$$ when treated with dilute mineral acids. For example, $${\rm{Mn}}{{\rm{O}}_2},{\rm{Pb}}{{\rm{O}}_2},{\rm{C}}{{\rm{O}}_2},{\rm{N}}{{\rm{O}}_2},$$ etc.

c. Superoxide: These oxides contain $${\rm{O}}_2^ –$$ unit, where each O atom has an oxidation state $$-1/2$$. All superoxides contain an odd number of valence electrons (i.e., $$13$$ electrons) and are therefore paramagnetic in nature. e.g. $${\rm{K}}{{\rm{O}}_2},{\rm{Rb}}{{\rm{O}}_2},{\rm{Cs}}{{\rm{O}}_2},$$ etc.

III. Suboxide: These oxides contain fewer oxygen atoms than are required for the normal oxide in the oxidation state of $$-2$$. For example, nitrous oxide $$\left( {{{\rm{N}}_2}{\rm{O}}} \right)$$, carbon suboxide $$\left( {{{\rm{C}}_3}{{\rm{O}}_2}} \right)$$, etc.

IV. Mixed oxide: Metal Oxides which consist of two simple metal oxides with the metal in different oxidation states are called mixed oxides.

## Simple Oxides

Binary compounds are formed when oxygen reacts with a wide range of metals and nonmetals. These binary compounds are referred to as oxides. Several elements can combine to form more than one type of oxide. Carbon, for example, produces both carbon monoxide and carbon dioxide. The characteristic properties of element oxides vary greatly. They may also differ in the type of bonding that exists in them. On the basis of the acid-base characteristics, oxides may be classified into the following categories.

### 1. Acidic Oxides

The oxide that combines with water to form acid is called Acid oxide. Acidic oxides are the binary compounds formed by combining nonmetals with oxygen. These are generally covalent Compounds. Some examples of this type of oxides are $${\rm{C}}{{\rm{O}}_2}$$ (carbon dioxide), $${{\rm{B}}_2}{{\rm{O}}_3}$$ (diboron trioxide), $${{\rm{N}}_2}{{\rm{O}}_5}$$ (dinitrogen pentoxide), $${\rm{S}}{{\rm{O}}_2}$$ (sulphur dioxide), $${\rm{S}}{{\rm{O}}_3}$$ (sulfur trioxide): $${\rm{C}}{{\rm{l}}_2}{{\rm{O}}_7}$$ (dichlorine heptoxide) etc. When treated with water, they form acids. For example,

### 2. Basic Oxides

The oxide that combines with water to form a base is called the basic oxide. Basic oxides are formed by the combination of strongly electropositive metals with oxygen and are generally ionic in nature. Some examples of this type of oxide are $${\rm{N}}{{\rm{a}}_2}{\rm{O}}$$ (sodium oxide), $${{\rm{K}}_2}{\rm{O}}$$ (potassium oxide), $${\rm{MgO}}$$ (magnesium oxide), $${\rm{CaO}}$$ (calcium oxide), $${\rm{BaO}}$$ (barium oxide) etc. These oxides dissolve in water to form basic solutions.

$${\rm{N}}{{\rm{a}}_{\rm{2}}}{\rm{O}}({\rm{s}}){\rm{ + }}{{\rm{H}}_{\rm{2}}}{\rm{O}}({\rm{l}}) \to {\rm{2NaOH}}({\rm{aq}}.)$$

$${\rm{CaO}}({\rm{s}}){\rm{ + }}{{\rm{H}}_{\rm{2}}}{\rm{O}}({\rm{l}}) \to {\rm{Ca}}{({\rm{OH}})_{\rm{2}}}({\rm{aq}}.)$$

$${\rm{BaO}}({\rm{s}}){\rm{ + }}{{\rm{H}}_{\rm{2}}}{\rm{O}}({\rm{l}}) \to {\rm{Ba}}{({\rm{OH}})_{\rm{2}}}({\rm{aq}}.)$$

### 3. Amphoteric Oxides

Oxides that have both acidic and basic properties are called amphoteric oxides. They react with both bases and acids to form salts.

Amphoteric oxides are formed by the elements that are on the borderline between metals and nonmetals, i.e. through the elements in the middle of the periodic table Some examples of this type of oxides are $${\rm{A}}{{\rm{l}}_2}{{\rm{O}}_3},{\rm{Si}}{{\rm{O}}_2},{\rm{ZnO}},{\rm{PbO}},{\rm{SnO}},$$ etc. As mentioned above amphoteric oxides react with both acids and bases to form salts.

### 4. Neutral Oxides

These oxides are neutral to litmus paper, and they do not react with acids or bases. Some examples of neutral oxides are $${{\rm{N}}_2}{\rm{O}},{\rm{CO}},{\rm{NO}},$$ etc.

## Mixed Oxides

Metal Oxides which consist of two simple metal oxides with the metal in different oxidation states are called mixed oxides. These mixed oxides show the properties of both the metal oxides simultaneously.

For example,

i. Red lead is considered a mixture of two oxides, lead oxides and lead dioxide and has the formula $${\rm{Pb}}{{\rm{O}}_2}.2{\rm{PbO}}$$ or $${\rm{P}}{{\rm{b}}_3}{{\rm{O}}_4}$$.

ii. Similarly, a magnetic oxide or ferromagnetic oxide $$\left( {{\rm{F}}{{\rm{e}}_3}{{\rm{O}}_4}} \right)$$ is considered a mixture of iron oxide $$\left( {{\rm{F}}{{\rm{e}}_2}{{\rm{O}}_3}} \right)$$ and iron(II) oxide $$({\rm{FeO}})$$ and has the formula $${\rm{F}}{{\rm{e}}_2}{{\rm{O}}_3} \cdot {\rm{FeO}}$$. Consequently, it gives a mixture of ferric and ferrous salts on treatment with acids.

$${\rm{F}}{{\rm{e}}_2}{{\rm{O}}_3} \cdot {\rm{FeO}} + 8{\rm{HCl}} \to 2{\rm{FeC}}{{\rm{l}}_3} + {\rm{FeC}}{{\rm{l}}_2} + 4{{\rm{H}}_2}{\rm{O}}$$

## Trends in Acid-Base Behaviour of Oxides in the Periodic Table

I. On moving from left to right in a given period in the periodic table, the nature of the oxides shows a gradual variation from strongly basic through amphoteric to strongly acidic.
For example,

II. Amongst s-block elements, on moving down the group, the basic character of the oxides increases. For example,

III. Among p-block elements, on moving down the group, the acidic character of the oxides decreases while the basic character increases. For example, in group $$13$$, the acidic character of oxides decreases and basic character increases as shown below.

IV. Among non-metallic oxides, the acidic character increases as the oxidation state of the non-metal increases. For example,

V. Among d-block elements, the basic character decreases and the acidic character increases with an increase in the oxidation state of the element.

## Summary

Oxides are binary compounds of metals and nonmetals with oxygen. Oxide can be simple or mixed. Binary compounds formed when oxygen reacts with a wide range of metals and nonmetals are known as simple oxides. On the basis of the acid-base characteristics, simple oxides may be classified into four types, and these are acidic oxides, basic oxides, amphoteric oxides and neutral oxides. Metal oxides which consist of two simple metal oxides with the metal in different oxidation states are called mixed oxides. These mixed oxides show the properties of both the metal oxides simultaneously.

## FAQs on Simple Oxides

Q.1. What are simple Oxides?
Ans:
Binary compounds formed when oxygen reacts with a wide range of metals and nonmetals in $$-2$$ oxidation state are known as simple oxides.

Q.2. What are simple and mixed oxides?
Ans:
Binary compounds formed when oxygen reacts with a wide range of metals and nonmetals in $$-2$$ oxidation state are known as simple oxides. Metal Oxides which consist of two simple metal oxides with the metal in different oxidation states are called mixed oxides.

Q.3. What are examples of basic oxides?
Ans:
The oxide that combines with water to form a base is called the basic oxide. Examples of basic oxides are $${\rm{N}}{{\rm{a}}_2}{\rm{O}}$$ (sodium oxide), $${{\rm{K}}_2}{\rm{O}}$$ (potassium oxide), $${\rm{MgO}}$$ (magnesium oxide), $${\rm{CaO}}$$ (calcium oxide), $${\rm{BaO}}$$ (barium oxide) etc. These oxides dissolve in water to form basic solutions.

Q.4. What are different types of oxides?
Ans:
The different types of oxides are as follows:
1. Simple oxides
2. Peroxide
3. Super oxide
4. Suboxide
5. Mixed oxide

Q.5. How are simple oxides classified?
Ans:
On the basis of the acid-base characteristics, simple oxides may be classified into the following categories.
1. Acidic oxides
2. Basic oxides
3. Amphoteric oxides
4. Neutral oxides

Q.6. What are examples of the five neutral oxides?
Ans:
Till now there are only five neutral oxides discovered. These are nitrous oxide, nitric oxide, carbon monoxide, manganese(IV) oxide and water.

Study About Oxides of Sulphur Here

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