Science, Tech, Math › Science Mole Definition in Chemistry Share Flipboard Email Print artpartner-images, Getty Images Science Chemistry Basics Chemical Laws Molecules Periodic Table Projects & Experiments Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College 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. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated July 03, 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.