Skeleton equations are created by placing the reactants, separated by plus signs, on the left-hand side, and the products on the right-hand side. These skeleton equations are generally unbalanced because they imply that only one molecule of each reactant and product is involved, which is not always the case.
In a chemical reaction, atoms or molecules of two or more reactants combine to form a product or products. Any molecules are made up of atoms. In a balanced equation, the total number of atoms on the left-hand side is equal to that on the right hand, and all chemical reactions have balanced equations.
A skeleton equation is used as a step towards a balanced equation and is used to jot down reactants and products before the balancing of the equation is performed.