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How to Indicate the Number of Atoms of Each Element in a Molecular Compound

A molecular compound is made up of two or more different types of atoms. The atoms found in the compound are represented by the chemical symbols of the element, and a numerical subscript to the right of each symbol. This subscript shows the number of atoms of the element present in the compound. If there is only one atom of the element, there is no subscript. The number of molecules present is shown by a number written in front of the molecule. For example, two molecules of salt would be written 2NaCl.

Instructions

- 1
  Determine the number of atoms of each element found in the molecular compound. For example, water has two atoms of hydrogen and one atom of oxygen.
- 2
  Write the molecular formula using subscripts. Water is written H^2O, with the 2 written at the bottom corner of the H as a subscript indicating two atoms of hydrogen. Depending on the level of the class, you might be asked to write the formulas resembling the way they combine in the molecule, or strictly by element and number. For example, acetic acid would be written: CH^3COOH to show how the molecule is formed, or C^2H^4O^2 to show just the number of atoms of each element in the compound.
- 3
  Use parentheses around polyatomic ions that are used more than once in the formula. Don't break up the ion, it retains its own identity within the compound. For example, ammonium (NH^4) sulfate (SO^4) is written: (NH^4)^2SO^4. Two ammonium ions combine with one sulfate ion.

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