There are approximately 602,214,179,300,000,000,000,000 molecules in one mole of any substance (this quantity is called Avogadro's number). Avogadro constant - Wikipedia, the free encyclopedia. The mass of an electron is approximately 0.0000000000000000000000000009109382 grams. Electron rest mass - Wikipedia, the free encyclopedia. Notice these two values are inconvenient to write in regular decimal notation because there are so many digits to write.