How numbers of atoms and molecules are shown in formulas and equations:

• Subscripts are small numbers to the lower right of a chemical symbol. They represent the number of atoms of the element in the compound.
   
• Coefficients are large numbers to the left of chemical formulas in equations. They represent the ratio of molecules of each substance involved in a chemical reaction.
   
• Subscripts and coefficients of 1 are "understood" - NEVER WRITTEN in chemical formulas and equations.
   
• The subscripts indicate a "ratio" in which atoms combine to make compounds.

  For H₂O - the ratio is 2 to 1 . . . 2 hydrogen atoms to 1 oxygen atom

To determine the total oxidation number, multiply the subscript by the oxidation number.

Example: the chemical formula for water is H₂O

Hydrogen = ( Oxidation # ) ( Subscript ) = ( +1 ) ( 2 ) = + 2
Oxygen = ( Oxidation # ) ( Subscript ) = ( −2 ) ( 1 ) = −2

Total oxidation numbers in water = ( +2 ) + ( −2 ) = 0