Mole Definition in Chemistry

different sized weights

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by Anne Marie Helmenstine, Ph.D.
Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels.
Updated February 06, 2019

A Mole is defined as a chemical unit, defined to be 6.022 x 1023 (Avogadro's Constant) entities. In science, this is usually molecules or atoms. The mass of a mole is the gram formula mass of a substance.

Examples:

  • 1 mole of NH3 has 6.022 x 1023 molecules and weighs about 17 grams (Nitrogen's molecular weight is 14 and Hydrogen is 1, 14 + 3 = 17).
  • 1 mole of copper has 6.022 x 1023 atoms and weighs about 63.54 grams.