How to Calculate Atoms to Moles to Grams


In chemistry, a mole does not dig tunnels underground; it represents a very large number of atoms, molecules or other microscopic particles. In the case of converting from atoms to moles, one mole contains 6.022 x 10^23 atoms. Moles also have another useful property: one mole of any substance has a mass in grams equal to the molecular weight of that substance. Armed with an understanding of the mole's properties and a periodic table, you can convert from atoms to molecules to grams for any substance.

Things You'll Need

  • Scientific calculator
  • Periodic table
  • Divide the number of atoms by Avogadro's number: 6.022 x 10^23 -- to find the number of moles. If you have 5 x 10^24 atoms of nitrogen, for example, divide by 6.022 x 10^23 to get 8.3 moles of nitrogen.

  • Look up the element on a periodic table and record the number under the element's symbol in grams per mole to get molecular weight. The symbol for nitrogen is N, for example, and the number under the N on the periodic table is 14.0067, so the molecular weight of nitrogen is 14.0067 g/mol.

  • Multiply the molecular weight by the number of moles to get the mass. For 8.3 moles of nitrogen, for example, multiply by 14.0067 g/mol to get 116.26 g of nitrogen.

Tips & Warnings

  • The same procedure works to convert between molecules, moles and grams -- just make sure to add the molecular weights of all the atoms in the molecule before multiplying by the number of moles.
  • Make sure to read the molecular weight rather than the atomic number from the periodic table. Generally the molecular weight is beneath the element's symbol and the atomic number is above it. You can double-check by noting whether your number has a decimal point; atomic numbers are always whole numbers.


  • Photo Credit Hemera Technologies/ Images
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