Acidic/Basic/Amphoteric/Neutral Oxides

An oxide is an oxygen ion with an oxidation state of -2 or O2-. A chemical compound with the anion O2- is an oxide. Some people use the term to refer to any chemical in which the anion is oxygen. There are many types of oxides, but the most common are metal oxides (such as Ag2O and Fe2O3). Metals react with oxygen in the air or water to form oxides, and metal oxides can become gaseous oxides at high temperatures. Water is a liquid oxide at normal temperature. Other oxides in the air include nitrogen dioxide (NO2) and sulphur dioxide (SO2) as well as carbon monoxide and carbon dioxide (CO2).

Based on the strength of their acid-base reactions, we can classify oxides as basic oxides, acidic oxides, amphoteric or neutral oxides.

Basic oxide

Oxygen reacts with metals to form basic oxides. Because oxygen and metals have different electronegativity, most basic oxides are ionic in nature. They have ionic bonds between atoms. By reacting with water, these oxides produce basic compounds.  Water’s pH rises when we add a basic oxide due to the formation of hydroxyl ions (OH–). Na2O, CaO, and MgO are some examples of common basic oxides. The example below shows a basic oxide dissolving in water.

Na2O + H2O → 2NaOH

Acidic oxide

A non-metal reacting with oxygen forms acidic oxides. Acid oxides react with water to form aqueous acids. These acid compounds contain oxygen, hydrogen, and non-metal atoms linked by covalent bonds. When dissolved in water, these acid compounds produce the acid compound of the oxide. For example, we refer to sulphur dioxide as sulphurous anhydride, while we refer to sulphur trioxide as sulphuric anhydride. Acid oxides can produce salt when they react with a base. Acid oxides typically have low melting and boiling points, except silicon dioxide, forming giant molecules. These oxides dissolve in bases to form salts and water. The formation of H+ ions occurs when an acidic oxide dissolves in water, lowering the pH. Acidic oxides include CO2, P2O5, NO2, SO3, etc. The following reaction is an example of acidic oxide dissolving in water.

SO3 + H2O → H2SO4

Amphoteric oxide

Amphoteric oxides are oxides that can be both acidic and basic. Amphoteric oxides can neutralise acids and bases because they contain acidic and basic oxides.

Amphoteric oxides form alkaline solutions when dissolved in water. Hydroxide ions are present in alkaline solutions. As a result, aluminium oxide (Al2O3) reacts with hydrochloric acid to produce aluminium chloride and water. It produces sodium aluminate (NaAlO2) and water from sodium hydroxide solution. ZnO, SnO, and PbO are three other examples of amphoteric oxides.

Neutral oxide

When reacting with water, neutral oxides show neither basic or acidic properties. Some examples include nitric oxide (NO), nitrous oxide (N2O), and carbon monoxide (CO), all of which have low water solubility.

Oxide property trends 

The periodic table has electropositive elements on the left. The electropositive nature gradually decreases along the period and elements are found with increasing electronegative character. The metalloids between electropositive metals and electronegative non-metals show the property change.

Electropositive metals produce basic oxides. The oxides become increasingly acidic as electronegativity increases. First group elements form strongly basic oxides, while the seventh group elements form strongly acidic ones — the more electronegativity an element has with oxygen, the more acidic the oxide is.

Conclusion

This article covers all oxide types with examples. Oxides are chemical compounds containing one or more oxygen atoms and either a metal or a nonmetal as a bonding agent.Solid oxides make up the majority of the Earth’s crust. Because oxygen is a highly electronegative element, it may create stable oxides with practically any other element. However, the tendency of oxygen to create oxides can be detrimental under particular circumstances because it corrodes metals and weakens metal-based items.When classifying oxides, one can study the nature of their formation to see if it is at the surface or bulk. The structure of the oxide can also be categorised as polymeric, molecular, or compound.