Oxides are binary compounds formed by the reaction of oxygen with other elements. Oxygen is highly reactive in nature. They react with metals and non-metal to form oxides.
Oxides as most of the things are are classified into neutral, amphoteric and basic or acidic based on their acid-base characteristics.
- An acidic oxide is an oxide which when combined with water gives off an acid.
- A basic oxide is an oxide which when combined with water gives off a base.
- When a substance reacts chemically, both as a base or acid it termed as an amphoteric solution.
- Neutral Oxide is one which is neither has an acidic characteristic or a basic one.
Metal Oxides have an oxidation number of -2 and generally comprise of an oxygen anion. The Earth’s crust is mostly made up of oxides that are solid. Oxide coatings can get formed over pure elements too, for instance a foil made of aluminum gets covered by a thin skin of Al2O3, and this skin defends the rest of the foil from corrosion.
Depending upon the nature and the properties exhibited by compounds, they are classified into
- Acidic oxides
- Basic oxides
- Amphoteric oxides
- Neutral oxides
Metals react with oxygen to give basic compounds of oxygen. These compounds are usually ionic in nature. Group 1, 2 and lanthanides form basic compounds of oxygen when they react with dixoygen. During the formation of these compounds a large amount of energy is released. These compounds readily react with water except few exceptions.
Examples: M2O3, MO2, ThO2
Na2O + H2O → 2NaOH
Non-metals react with oxygen to form acidic compounds of oxides which are held together by covalent bonds. These compounds can also be called as acid anhydrides. Acid anhydrides usually have a low melting and boiling point except compounds like B2O3 and SiO2 which have high melting points and form giant molecules.
Examples: NO, CO2
SO3 + H2O → H2SO4
B2O3 + H2O → 2H3BO3
Amphoteric oxides are compounds of oxygen which exhibits both acidic as well as basic characteristics. These oxides when react with acid, undergoes neutralization reaction to form water and salt. This exhibits the basic property of the compounds. Similarly reacts with alkali to form salt and water, exhibiting acidic property. Example: aluminium oxide
AL2O3 + 6HCl → 2Al 3+ + 6Cl– + 3H2O
Al2O3 +2OH– + 3H2O → 2[Al (OH) 4]–
Some compounds react with oxygen to form oxides which does not exhibit acidic nor basic characteristics. Such compounds are called as neutral compounds of oxygen.
Example: NO, CO.
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