An oxide is a chemical compound in which one or more oxygen atoms combined with another element, such as H2O or CO2. Based on their acid-base characteristics, oxides can be classified into four categories: acidic oxides, basic oxides, and amphoteric oxides and neutral oxides.[according to whom?]
A basic oxide, also called a base anhydride (meaning "base without water"), is usually formed in the reaction of oxygen with metals, especially alkali (group 1) and alkaline earth (group 2) metals. Both of these groups form ionic oxides that dissolve in water to form basic solutions of the corresponding metal hydroxide:
Alkali metals (Group 1)
X2O + H2O → 2XOH (X = group 1 element)
Alkaline earth metals (group 2)
XO + H2O → X(OH)2 (X = group 2 element)
For example, the basic oxide Li2O becomes the hydroxide LiOH, and BaO becomes Ba(OH)2 after reacting with water. In contrast, non-metals usually form acidic oxides. In general, the basicity of oxides increases when towards the lower-left corner of the periodic table, which corresponds to increased metallic properties.[1]
Examples
All oxides of group 1 & 2 elements are basic (except BeO), they react with water to form a base:[2]
