Avogadro’s number NA is the number of atoms in 12 grams of carbon-12. It’s about 6.02 × 1023. (Update: Avogadro’s number is now exactly NA = 6.02214076 × 1023 mol-1 by definition. More details here.)
Here are a few fun coincidences with Avogadro’s number.
- NA is approximately 24! (i.e., 24 factorial.)
- The mass of the earth is approximately 10 NA kilograms.
- The number of stars in the observable universe is 0.5 NA.
For more constants that approximately equal factorials, see the next post.