Classification of Oxides

Q: What are two examples of oxides?

Examples of acidic oxides are Sulphur dioxide (SO 2 ) and sodium oxide (Na 2 O).

Classification of Oxides - Dioxides, Example, Formula, Classification and FAQs

Edited By Team Careers360 | Updated on Jul 02, 2025 04:57 PM IST

What are Oxides?

Oxide is an element that combines with the binary compound of oxygen to form a new element. Most metals in the periodic table react with oxygen to generate oxides. One element can often produce two or more oxides. The nature and properties of oxides vary greatly. When the elements react with oxygen, they produce dioxides (MO₂) and tri oxides (MO ) (where M=Sulphur, Selenium, Tellurium, and other elements.

This Story also Contains

What are Oxides?
Example of Oxides
Oxide's Chemical Formula
Classification of Oxides
Oxides' Characteristics
Oxides of metals
Metal Reactions with Metal Oxide:

Example of Oxides

Carbon dioxide, sulphur dioxide, calcium oxide, carbon monoxide, zinc oxide, barium peroxide, and water are examples of oxides. Because oxygen is combined with only one element, these are called oxides.

Dioxides

Dioxide is an oxide that has two atoms of oxygen, each linked directly to an atom of a different element. These can be made by igniting the element in the atmosphere.

S+O₂→SO₂

Trioxide is an oxide that comprises three oxygen atoms, each linked directly to an atom of a different element. The most important trioxide is SO₃

2SO₂+O₂→2SO₃

It is sulfuric acid's anhydride.

SO₃+H₂O→H₂SO₄

Trioxides are also produced by the element’s selenium and tellurium.

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Oxide's Chemical Formula

A negatively charged oxygen atom is called an oxide ion. It has gained two electrons from another atom in this way. O₂^– is the oxide symbol.

12O₂(g)+2e^–→O₂^–

Oxides are divided into two categories:

Simple oxides are oxides that contain only the number of oxygen atoms permitted by the metal's usual valency. Acidic, basic, neutral, and amphoteric oxides are the four types of simple oxides. Simple oxides include magnesium oxide and aluminium oxide, to name a few.

Oxides of Mixed Composition

Mixed oxides are oxides that are made up of two comparable oxides. The elements in the two simple oxides could be the same or different. Let's go through mixed oxides in greater detail. When lead dioxide (PbO₂) and lead monoxide (PbO) are combined, Red Lead is formed (Pb₃O₄).Ferric oxide (Fe₂O₃) and ferrous oxide (FeO) combine to generate Ferro-Ferric Oxide, a mixed oxide (Fe₃O₄). Magnetic Oxide is another name for this substance. Ilmenite is a ferrous oxide (FeO) and titanium oxide (TiO) mixed oxide (TiO₂). A mixture of SrO and TiO₂ is called a Strontium Titanate (SrTiO₃).

Oxides' Characteristics

Different qualities can aid in the differentiation of the three types of oxides.

Oxide of Acid

Acidic oxide is an oxide that reacts with water to form an acid. Bases, such as sodium hydroxide, are neutralised by them. Acidic anhydrides are compounds that dissolve in water to produce acids. Sulphur dioxide, Cl₂O₇, and other compounds are examples.

Sulphur trioxide (SO₃), for example, dissolves in water to form sulphuric acid (H₂SO₄).

SO₃+H₂O→H₂SO₄

Carbon dioxide (CO₂) dissolves in water to form carbonic acid in the same way (H₂CO₃).

CO₂+H₂O→H₂CO₃

Acidity is a property of non-metallic oxides. Acids are formed when acidic oxides of non-metals dissolve in water. Non-metal acidic oxides change the colour of the water.

Oxide of Basic

Basic oxides are oxides that react with water to form a base. Examples are Na₂O, CaO, and BaO. Acids such as hydrochloric acid are neutralised by them. They form bases when they dissolve in water. Basic anhydrides are what they're termed.

Na₂O+H₂O→ 2NaOH,

CaO+H₂O→Ca(OH)₂

Metallic oxides are, in general, basic. The resulting solution turns red litmus blue when they react with water. Basic oxides are oxides that fall into this category.

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Oxide of Amphoteric

Metallic oxides with both basic and acidic characteristics are known as amphoteric oxides. They produce salt and water when they react with an acid, demonstrating basic characteristics. However, when they react with alkalis, they produce salt and water, both of which have acidic qualities.

ZnO+2H₂O + 2NaO→ Na₂Zn(OH)₄ + H₂

ZnO+2HCl→ZnCl₂+H₂O

Another example is aluminium oxide, which reacts with both alkalis and acids.

When aluminium oxide reacts with hydrochloric acid, it becomes a basic oxide.

Al₂O₃(S)+6HcL(aq) →2AlCl₃(aq)+ 3H₂O

Aluminium oxide + Hydrochloric acid→ Aluminium chloride + Water

Water

When aluminium oxide reacts with sodium hydroxide, it forms an acidic oxide.

Al₂O₃(S) +2NaOH(aq) → 2NaAlO₂(aq) + H₂O(l)

Aluminium oxide + Sodium hydroxide → Sodium Aluminate + Water

Oxides with a neutral pH

Some oxides are neutral in nature, meaning they are neither acidic nor basic. Neutral oxides are the name given to such oxides. Nitrous oxide and carbon monoxide are examples of neutral oxides. Oxides in a Period and Group have acidic and basic natures. With an increase in the electropositivity of metal producing oxide, the basic character of the oxides normally increases. All group 1 oxides are basic, while group 17 oxides are acidic. The basic nature of oxides rises as they progress in the group, whereas the acidic nature decreases.

The basic nature of oxides steadily declines with time, whereas the acidic nature gradually increases. When a single element generates a large number of oxides, the acidic nature of the compound increases as the number of oxygen atoms grows. Caesium oxide is the most basic oxide. The strongest base is calcium hydroxide. Chlorine heptoxide is the most acidic oxide. The most powerful acid is perchloric acid.

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Oxides of metals

Metal oxides are crystalline solids with a metal cation and an oxide anion. Salts are formed when they react with acids, and bases are formed when they react with water.

Metal Oxide Preparation: Metal oxides can be prepared in two ways:

Using the direct way

Method of indirection

In the direct method, metals react with oxygen to form metal oxides.

Example: 2Ca+O₂ → 2CaO

2Mg+O₂ → 2MgO

Thermal breakdown of carbonate salts, hydroxides, and nitrates is used in the indirect technique.

Example:

CaCO₃ → CaO + CO₂

2Pb(NO₃)₂→ 2PbO + 4NO₂ + O₂

Metal Oxides and Acids Reaction:

When metal oxides react with acids, salts are formed. Magnesium oxide, calcium oxide, Sodium oxide, and potassium oxide are examples.

MgO+2HCl→MgCl₂+H₂O

CaO+H₂SO₄→CaSO₄+H₂O

Metal Reactions with Metal Oxide:

This reaction appears to be a ‘competition' for oxygen atoms between two metal atoms. The oxygen will be removed from the less reactive metal oxide by the more reactive metal atoms. The oxygen is transferred from the less reactive metal oxide to the more reactive metal as a result of this process. The more reactive metal always pulls oxygen away from the less reactive metal oxide, according to the rule.

Mg+CuO→Cu+MgO

Also check-

NCERT Chemistry Notes:

Frequently Asked Questions (FAQs)

1. What are two examples of oxides?

Examples of acidic oxides are Sulphur dioxide (SO₂) and sodium oxide (Na₂O).

2. What is the process of forming an oxide?

An oxide is a binary compound of oxygen and another element. Oxygen has a high reactivity. They create oxides when they react with metals and non-metals. Sulphides form sulfoxides, while amines form amine oxides, in which the oxygen atom is covalently bound to the Nitrogen or Sulphur atom.

3. What are neutral oxides, and what are some examples of them?

Some oxides are neutral in nature, meaning they are neither acidic nor basic. Neutral oxides are the name given to such oxides. Nitrous oxide, water, and nitric oxide are examples of neutral oxides.

4. What is the purpose of oxide?

Oxides are employed in the laboratory to make salts and in the production of slag. As a drying agent, certain oxides are utilised.

5. What are the different types of basic oxides? Could you give an example?

Basic oxides are oxides that form a base when mixed with water.

Examples are Na₂O, CaO, and BaO.

6. Is carbon dioxide an oxide or a gas?

Carbon dioxide is a very acidic gas. Acids are formed when acidic oxides of non-metals dissolve in water.

7. Write neutral oxides examples.

Nitrous oxide, carbon monoxide are neutral oxide examples.

8. List examples of basic oxides.

Magnesium oxide, Sodium oxide are examples of basic oxides.

9. Metal oxide acid or base?/ metal oxides are acidic or basic?

Metal oxides are basic.

10. How are oxides classified?

Oxides are generally classified into four main categories: acidic oxides, basic oxides, amphoteric oxides, and neutral oxides. This classification is based on their behavior in water and their reactions with acids and bases.

11. What are dioxides?

Dioxides are a specific type of oxide containing two oxygen atoms bonded to another element. The general formula for dioxides is XO2, where X represents the other element.

12. Give examples of neutral oxides.

Examples of neutral oxides include carbon monoxide (CO), nitrous oxide (N2O), and water (H2O) itself.

13. What is the difference between a monoxide and a dioxide?

A monoxide contains one oxygen atom per formula unit (XO), while a dioxide contains two oxygen atoms per formula unit (XO2). For example, carbon monoxide (CO) vs. carbon dioxide (CO2).

14. How do mixed oxides differ from simple oxides?

Mixed oxides contain two or more different metal elements combined with oxygen, unlike simple oxides which contain only one metal element. Mixed oxides often have unique properties and applications, such as in ceramic materials.

15. Can you give examples of common dioxides?

Common examples of dioxides include carbon dioxide (CO2), silicon dioxide (SiO2), sulfur dioxide (SO2), and titanium dioxide (TiO2).

16. What is the importance of silicon dioxide in technology?

Silicon dioxide (SiO2) is crucial in technology, serving as the base material for computer chips, fiber optic cables, and as an insulator in electronic devices. It's also the primary component of glass.

17. How do oxides contribute to the colors of gemstones?

Many gemstones owe their colors to the presence of metal oxides. For example, the red color of rubies is due to chromium oxide, while the blue color of sapphires is caused by iron and titanium oxides.

18. What is the greenhouse effect and how are oxides involved?

The greenhouse effect is the warming of Earth's surface due to certain gases trapping heat in the atmosphere. Carbon dioxide (CO2), a greenhouse gas, plays a significant role in this process, along with other oxides like nitrous oxide (N2O).

19. What is the difference between covalent and ionic oxides?

Covalent oxides are formed by nonmetals and involve sharing of electrons, resulting in molecules (e.g., CO2). Ionic oxides are formed by metals and involve electron transfer, resulting in a crystal lattice structure (e.g., Na2O).

20. What are amphoteric oxides?

Amphoteric oxides are oxides that can behave as both acidic and basic oxides, depending on the reaction conditions. They can react with both acids and bases.

21. What is the significance of oxide layers on metals?

Oxide layers on metals often serve as a protective coating, preventing further corrosion. This phenomenon, known as passivation, is particularly important for metals like aluminum and stainless steel.

22. How do oxides behave in acid-base reactions?

In acid-base reactions, acidic oxides react with bases to form salts and water, while basic oxides react with acids to form salts and water. Amphoteric oxides can react with both acids and bases.

23. What role do oxides play in the formation of minerals?

Oxides are crucial components of many minerals. For example, silica (SiO2) is the main component of quartz, and various metal oxides contribute to the formation of different types of rocks and minerals in the Earth's crust.

24. How does the structure of an oxide affect its properties?

The structure of an oxide, including its crystal lattice and bonding type, greatly influences its properties such as melting point, solubility, and reactivity. For instance, the different crystal structures of SiO2 (quartz, cristobalite, tridymite) exhibit different properties.

25. What is the role of oxides in glass formation?

Oxides are the primary components of most glasses. Silicon dioxide (SiO2) is the main glass former, while other oxides (like Na2O, CaO) act as network modifiers, altering the properties of the glass.

26. How do oxides contribute to the formation of acid rain?

Oxides of sulfur (SO2, SO3) and nitrogen (NO, NO2) released from industrial processes and combustion react with water in the atmosphere to form acids, leading to acid rain. This process can have harmful effects on ecosystems and infrastructure.

27. How do superoxides differ from regular oxides?

Superoxides contain the O2- ion, where oxygen has an oxidation state of -1/2. They are more reactive than regular oxides and are formed by highly electropositive elements like alkali metals.

28. What is the role of oxides in ceramic materials?

Oxides are fundamental components of many ceramic materials. They contribute to properties such as hardness, heat resistance, and electrical insulation. Examples include alumina (Al2O3) in high-temperature ceramics and zirconia (ZrO2) in thermal barrier coatings.

29. What is the role of oxides in battery technology?

Oxides are crucial components in many types of batteries. For example, lithium cobalt oxide (LiCoO2) is commonly used as a cathode material in lithium-ion batteries, while lead dioxide (PbO2) serves as the positive electrode in lead-acid batteries.

30. What determines whether an oxide is acidic or basic?

The acidity or basicity of an oxide is primarily determined by the position of the element in the periodic table. Generally, oxides of metals on the left side of the periodic table are basic, while oxides of nonmetals on the right side are acidic.

31. What is the behavior of basic oxides in water?

Basic oxides dissolve in water to form basic (alkaline) solutions. They react with water to produce hydroxides, increasing the pH of the solution.

32. Can you provide examples of amphoteric oxides?

Common examples of amphoteric oxides include aluminum oxide (Al2O3), zinc oxide (ZnO), and lead(II) oxide (PbO).

33. What is the importance of metal oxides in everyday life?

Metal oxides have numerous applications in daily life, including their use in construction materials (e.g., iron oxide in cement), pigments (e.g., titanium dioxide in white paint), and electronic components (e.g., silicon dioxide in computer chips).

34. How does the oxidation state of an element affect its oxide formation?

The oxidation state of an element determines the ratio of oxygen atoms it can bond with. Higher oxidation states generally lead to oxides with more oxygen atoms, such as dioxides or trioxides.

35. How do acidic oxides behave in water?

Acidic oxides dissolve in water to form acidic solutions. They react with water to produce acids, lowering the pH of the solution.

36. How do peroxides differ from regular oxides?

Peroxides contain an oxygen-oxygen single bond (O-O) in their structure, unlike regular oxides. They have the general formula X2O2 or XO2, where the oxidation state of oxygen is -1 instead of the usual -2.

37. How does the electronegativity of elements affect oxide formation?

Electronegativity influences the nature of the oxide formed. Highly electropositive elements (like metals) tend to form basic oxides, while electronegative elements (like nonmetals) usually form acidic oxides.

38. What are neutral oxides?

Neutral oxides are oxides that do not react with water to form acids or bases. They typically do not change the pH of water when dissolved.

39. How do oxides contribute to environmental issues?

Some oxides, particularly those of nitrogen and sulfur, contribute to environmental problems such as acid rain when released into the atmosphere. Carbon dioxide, a greenhouse gas, plays a significant role in climate change.

40. What are oxides?

Oxides are chemical compounds formed when oxygen combines with other elements. They consist of oxygen bonded to one or more other elements, typically metals or nonmetals.

41. How do oxides contribute to the chemistry of the Earth's atmosphere?

Oxides play crucial roles in atmospheric chemistry. For example, ozone (O3) in the stratosphere protects Earth from harmful UV radiation, while nitrogen oxides participate in complex reaction cycles affecting air quality.

42. How do oxides contribute to the hardness of minerals?

The presence and arrangement of oxide ions in mineral structures often contribute to their hardness. For example, the extreme hardness of diamond is due to its three-dimensional network of covalently bonded carbon atoms, while the hardness of corundum (Al2O3) is due to its densely packed oxide ions.

43. What is the significance of rare earth oxides in modern technology?

Rare earth oxides, such as those of neodymium, erbium, and yttrium, are crucial in various high-tech applications. They are used in lasers, phosphors for displays, magnets in electric motors, and as dopants in optical fibers.

44. What is the importance of titanium dioxide in everyday products?

Titanium dioxide (TiO2) is widely used as a white pigment in paints, plastics, and paper due to its high refractive index. It's also used in sunscreens for its UV-blocking properties and as a photocatalyst for self-cleaning surfaces.

45. What is the relationship between an element's position in the periodic table and its oxide's properties?

Generally, as you move from left to right across the periodic table, oxides tend to become more acidic. As you move from top to bottom, the acidity or basicity of oxides tends to increase in strength.

46. How do transition metal oxides differ from main group metal oxides?

Transition metal oxides often exhibit variable oxidation states, leading to multiple oxide forms. They also tend to have more complex structures and can display amphoteric behavior more frequently than main group metal oxides.

47. What is the role of oxides in catalysis?

Many metal oxides serve as important catalysts in industrial processes. For example, vanadium(V) oxide is used in the contact process for sulfuric acid production, and titanium dioxide is used in photocatalysis.

48. What is the role of iron oxides in biology?

Iron oxides play important roles in biology, such as in the formation of magnetite (Fe3O4) in magnetotactic bacteria for navigation, and in the storage of iron in ferritin proteins in animals.

49. How do oxides affect the properties of alloys?

Oxides can significantly influence alloy properties. They can form protective layers, enhance strength (as in oxide dispersion strengthened alloys), or act as impurities that affect mechanical and electrical properties.

50. What is the importance of transition metal oxides in magnetic materials?

Many transition metal oxides exhibit magnetic properties due to unpaired electrons. For instance, iron oxides like magnetite (Fe3O4) are ferrimagnetic and find applications in data storage devices and magnetic resonance imaging (MRI).

51. How do oxides affect the conductivity of materials?

The presence of oxides can significantly alter a material's electrical conductivity. Some metal oxides are insulators (e.g., Al2O3), while others can be semiconductors (e.g., ZnO) or even superconductors (e.g., certain copper oxides at low temperatures).

52. How do oxides affect the melting points of compounds?

Generally, ionic oxides have high melting points due to strong electrostatic forces in their crystal lattices. Covalent oxides typically have lower melting points, but some network covalent oxides (like SiO2) can have very high melting points due to their extensive 3D structure.

53. How do oxides contribute to the colors of transition metal compounds?

The color of many transition metal oxides and compounds is due to d-d electron transitions. The specific color depends on the metal, its oxidation state, and the surrounding ligands. For example, copper(II) oxide is black, while hydrated copper(II) ions in solution are blue.

54. How do metal oxides function as heterogeneous catalysts?

Metal oxides often serve as heterogeneous catalysts by providing active sites on their surfaces where reactants can adsorb and undergo reactions. The oxide's surface structure, defects, and electronic properties all play roles in its catalytic activity.

55. What is the role of oxides in geochemical processes?

Oxides play crucial roles in various geochemical processes. They are involved in mineral formation, weathering reactions, and can influence the mobility and availability of elements in the environment. For example, iron and manganese oxides can adsorb and immobilize heavy metals in soils and sediments.

56. How do oxides contribute to the properties of cement and concrete?

Oxides are major components of cement and contribute significantly to its properties. Calcium oxide (CaO) and silicon dioxide (SiO2) are the primary constituents, while smaller amounts of aluminum oxide (Al2O3) and iron oxide (Fe2O3) also play important roles in determining the cement's characteristics and performance.

57. What is the significance of oxide thin films in electronics?

Oxide thin films are crucial in many electronic devices. For example, silicon dioxide is used as an insulating layer in transistors, while transparent conducting oxides like indium tin oxide (ITO) are used in touchscreens and solar cells.

58. How do oxides affect the reactivity of metals?

Oxide layers on metal surfaces can significantly affect their reactivity. In some cases, like with aluminum, the oxide layer passivates the metal, protecting it from further corrosion. In other cases, the oxide layer may be porous or unstable, allowing continued reaction of the underlying metal.

59. What is the role of oxides in solid oxide fuel cells (SOFCs)?

In solid oxide fuel cells, oxides play critical roles. The electrolyte is typically a ceramic oxide like yttria-stabilized zirconia (YSZ), which conducts oxygen ions at high temperatures. The electrodes often contain mixed oxides that catalyze the electrode reactions and conduct both ions and electrons.