THE MOLE—as in 6.02214076×10^23, the unit in chemistry used to count really really tiny stuff like atoms and molecules. Well, THE MOLE changed (it’s not simply 6.022×10^23 anymore). And while you may not have noticed it, a fundamental shift in the way we measure things—not just on Earth, but throughout space and time—took place when the new mole was born. To show you how, we’ll count atoms inside one of the world’s most perfectly round spheres at the National Institute of Standards and Technology (NIST) outside of Washington, D.C.

Maybe you’ve heard of NIST—they do stuff like keep the official time for our country with their atomic clock. Which, when you think about it, is a pretty awesome thing. Basically, NIST is our country’s check and balance on, well, everything. From time to the dosage of a medication to what a nickel is made of. They also have the 130-year-old national prototype of the kilogram, known as K20. That kilogram and the international prototype it’s based on in France, Le Grand K, is central to the making of the new mole. Well, that and one of the most perfectly round objects in the world, a one kilogram sphere of silicon. And counting the atoms inside it is where our story starts.

—
Episode – Moles (part two)
“ A More Perfect Unit: The New Mole ”
Video by : Tom McNamara
Narrator : Eleanor Cummins
Animation : Ben Gabelman
Animation : Jason Drakeford
Additional camera : Erin Chapman
Online Director : Amy Schellenbaum

Editor-in-Chief : Joe Brown

MEDIA
Internet Archive, National Institute of Standards and Technology (NIST), Pond5, Wikimedia Commons

SPECIAL THANKS
Alison Gillespie (NIST), Dr. Savelas Rabb (NIST), Dr. Stephan Schlamminger (NIST), Dr. Bob Vocke (NIST); the Kibble Balance, K20, the mass spectrometer, the silicon sphere