Subscripts and Coefficients

by Katrina Carpenter


  • A subscript is the number that is written below the element that lets you know how many molecules of that element are present.
  • It tells you how many atoms of a certain element are present in a structure.
  • For example, hydrogen with a subscript of 2 would mean that there are two hydrogen molecules that are reacting in the reaction.


  • It gives the number of molecules (or atoms) involved in the reaction.
  • In other words they give the ratio that the molecules combine in.
  • For example, this is an unbalanced equation: N2 + O2 —> NO. Placing a coefficient of 2 before the product, however, will balance out the equation and is written as N2 + O2 —> 2NO.

Examples of Subscripts and Coefficients

Frequently Asked Questions

  1. What is the difference between a coefficient and a subscript? The placement of subscripts and coefficients are different and it tells you how the substances are put together on the atomic level.
  2. In balancing a chemical equation, why can you change coefficients, but not subscripts? The subscripts describe the ratios of elements present within molecules changing them would change the meaning of the formula.