A more perfect unit: The New Mole | EXPERIMENTALS: Moles (part 2)


[Narrator] Everything is made up of tiny things called atoms, but how many atoms make up everything. How do you quantify invisible stitches that make up the fabric of our universe? How do you even count that high? One word, moles. (light music) This is one of the everthings
made up of those tiny atoms, a nearly perfect sphere, one kilogram of a single
crystal of silicon. So how many atoms does it have? Well like all crystals this silicon sphere is made up of atoms in a
regularly repeating fixed pattern. Using a mass spectrometer to
calculate it’s molar mass, super powerful X-ray diffraction to measure the spacing of atoms, and laser interferometers
to determine it’s volume, you can literally count
the number of silicon atoms inside the sphere and that
number is 35.72759313 moles, give or take, but wait, how much is a mole of something. Well one mole is Avogadro’s number named for this 19th century chemist and that number is (laughing) – Just do the zero,
you’ll be the zero man. – I’ll be the zero man? – Yeah, why not? – Oh, well go ahead. – So Avogadro’s number is 602,214,076, – 000,000,000,000,000. (laughing) – [Narrator] That’s a little
more than 600 billion trillion. Said another way, 6.022214076
times 10 to the 23rd. Here’s the thing. That number is the redefined mole. Oh yeah, and while the mole is a number, it’s really a unit of measurement. You see in 1971 it joined
the kilogram, the second, the meter, the candela,
the ampere, and the kelvin as one of the seven base units in The International System of Units, the modern form of the metric system, and on May 20, 2019, the mole
along with three other units was officially redefined
thanks to the work of chemists Bob Vocke and Savelas Rabb at the National Institute
of Standards and Technology. Well them an a whole
international team of scientists, but before we get lost in all the zeros. – [Savelas] Zero, zero, zero. – [Narrator] Of old and new moles. – [Savelas] Zero, zero, zero. – [Narrator] Let’s take a step back. What is a mole? – [Interviewer] In one
word what is a mole? – In one word? – [Interviewer] Yeah. – A unit. – A mole is. – One word. – 6.02214076 times 10
to the 23rd entities. – [Narrator] So a mole is a unit. It’s used for measuring
really small things. – You needed to use it in order to change from molecules to grams
of whatever compound that you were using. You always need to know,
okay moles of this, or moles of that. – [Narrator] Moles are really practical. They translate things
from the atomic level to quantities you can see and touch. Chemists use moles to design reactions that produce exactly the
amount of substance they need without ever having to
actually count it’s atoms or molecules. It’s like this, you don’t count out grains of rice to go in a sushi roll. You measure rice using cups or grams. So the mole is a standard
way of measuring quantities, but long ago, like before
the metric system long ago, we didn’t have standard
ways of measuring anything. In fact, the story of
the mole’s redefinition starts way before it ever existed. It starts in France in
the late 18th century. (dramatic music) – We have kingdoms and counties
and dukes and what have you and all of these they
had different scales. (dramatic music) If you were a salesman and
you sold cloth for example, you crossed the county line and suddenly the yard was different. People at the time of
the Revolution thought this is actually not a good idea. We want to have a uniform
measurement system that doesn’t change, that’s
for all times of all people, it’s the coinage that
they used at the time. – [Narrator] Stephan
Schlamminger is a physicist at the National Institute
of Standards and Technology. Oh, and he’s wearing a hear net because a kibble balance
is right behind him. Forgive me this will be earlier. – Yeah. [Narrator] Ready? [Camera Man] Yes. Awesome. – There’s no rudeness that I haven’t had. (laughing) – [Narrator] What’s a
kibble balance you ask. It’s this awesomely precise electromagnetic measuring instrument, precise enough that a strand of hair could upset it’s measurements. More on a kibble balance later. So what Shlamminger is talking about. – A uniform measurement
system is for all times of all people. – [Narrator] Is the creation
of the metric system, because in France alone,
just prior to the Revolution, it’s estimated there were 250,000 different units of measurement in use. Okay, how does anybody start
standardizing measurements? Well you begin with the unit. Let’s consider the kilogram. Early on the kilogram was the mass of a liter of distilled
water at it’s freezing point. Then in 1799 a kilogram cylinder
was forged from platinum a physical, you can hold
it in your hand standard for the new metric system. In 1889 that prototype dubbed Le Grand K, was reforged out of a
platinum iridium alloy to increase it’s stability. Also it was locked in a vault. Oh, and what you’re
looking at here is K20, the American national prototype. Made in 1889 it’s an
exact copy of Le Grand K, but that was 130 years ago,
and what does all of this have to do with the
redefinition of the mole? – I think when people said
we want a measurement system for all times for all people,
I think it’s a very noble idea but I think they fell a
little bit short of it, ’cause everybody knows things change. It is part of the basic human experience. When you buy a new car, couple years later it
doesn’t look new anymore. So even this artifact kilogram, the national prototype of
a kilogram will change. – [Narrator] In Fact Le
Grand K is getting lighter, compared to it’s copies,
like the American prototype. It’s mass is off by 50 micrograms. Think the weight of a grain of salt. So in 2011 the world’s
measurement experts came together and passed a resolution
to redefine the kilogram. That’s also when the decision
was made to redefine the mole. Same with the Kelvin and
ampere, but redefined how. – In the new system of units we can use fundamental
constants of nature. They don’t depend on time or space. No matter where you are in the universe they have the same value, no matter of what time you are there, they have the same value. They are sort of baked into
the fabric of the universe. – [Narrator] So there’s
still a physical kilogram, but instead of a single object in a vault, the kilogram will be defined
by Planck’s constant, a number so small that it starts with 33 zeros after it’s decimal point, and you can find that number by dividing the amount of energy, a particle of light carries, by it’s electromagnetic frequency, but how does a tiny number and
electromagnetic frequencies help us define the kilogram. That’s where the kibble balance comes in. It weighs and electromagnetic
force against a mass, meaning in this case, it can tell you how much electromagnetic
force is equal to a kilogram and the answer is equal
to Planck’s Constant, but there’s another way
to define a kilogram. – There’s two different methods and one method is the kibble balance, and the other method
is the silicon sphere. (light music) – [Narrator] Ladies and
gentlemen, The Mole, Redefined. – Mole is a relatively new unit. So when it was brought
into the SI in 1971, it was defined on the
basis of the kilogram. – [Narrator] Right there, that’s the kilogram/mole connection, because before the redefinition, a mole was equal to the number of atoms in 12 grams of Carbon-12, which was about 6.022 times 10 to the 23rd atoms. That huge number represented the amount of elementary particles in a mole, meaning a mole was based
around a number of components, not it’s size or what it weighs. – If we look at a mole of carbon and a mole of aluminum they look different and that’s because this is packed in a very tight cubic structure. This is the more open structure and so the volume has nothing to do with the number of entities there. It has to do with the
crystalline structure. – [Narrator] Same number of
atoms, different size package. The thing is under the
old definition of a mole. – We didn’t know how many
things were in a mole, but we knew what it’s mass was. – [Narrator] So the definition of a mole was maybe more complicated
than it needed to be. That’s why an international
group of scientists decided to change things. Vocke and Rabb are part
of a world wide team called the International Avogadro Project. Their mission, to measure the
mole, aka Avogadro’s number as precisely as possible and from there redefine the mole. – But we knew the mass, but we didn’t know the number of entities. What we’ve done is we’ve
flipped that on it’s head now and we’ve defined the number of entities. We’re in affect making something
where we’re counting atoms which is about the most
basic things humans do. We’ve counting things
since Babylonian times. – [Narrator] Remember counting
atoms in that silicon sphere? A sphere just like it redefined the mole, a sphere of silicon-28. – So it was, so yeah, so the
sphere that I was holding actually represents a kilogram. It’s not necessarily a
mole, but it can be used in order to determine
what a mole of silicon is. – [Narrator] To make it
enriched silicon was grown into a purified crystal and
shaped into this object, one of the most perfectly
round things in the world. The scientists of the
International Avogadro Project worked for years to
figure out how to count each atom inside it’s curves. First, precise nanometer scale
measurements of it’s volume. Then a new set of technologies and methods to make an
even trickier measurement, the space between atoms inside the silicons crystalline structure. – If you have a volume and
you have a grid inside it you can count how many little
things you have inside there, you can calculate it. – It’s still abstract in
saying we are counting atoms, it’s, we can’t see it visually, but the instrument can see it. – [Narrator] With these points of data the researchers could calculate the total number of atoms in the sphere. Drum roll please. The value of Avogadro’s
Constant, the value of the mole, is now 6.02214076 times 10 to the 23rd and now a mole isn’t
determined by a kilogram, but that doesn’t mean they’re
totally disconnected either. – Deep in physics there’s
somewhere an equation that relates Avogadro’s Constant and Planck’s constant together. So if you know one you know the other, but the interesting thing is, is the experiment that
measure Avogadro’s constant came more out of chemistry and the experiment that
measures Planck’s constant came more out of physics. This is a miracle in itself
that these two fields, chemistry and physics,
they’re so big and wide that they can make an agreement. I think this is pretty amazing. – [Narrator] Just as a kilogram is now defined by a universal
constant, so is the mole. – So you can take these measurements, put them in the, I’m not
gonna say magical equation, but into the equation to determine, okay, are we getting the same
value for Avogadro’s constant that someone else in another country, or even in another lab, are
they getting the same values. The measurements are available to anyone as long as they the instrumentation, but it’s available to get. – [Narrator] So why do universal
constants for kilograms and moles even matter? – You have people that wanna
do fundamental research, thy want, you know I wanna
discover the new thing. Ours is not about discovering
the next new thing. It’s about making the
measurement of that thing. – Big circle. – As accurate and as well
characterized as possible, for as many people as possible. The SI units are practical units. They’re meant, they’re
intended for commerce and so everyone has to basically agree that this is the way the wanna do it, they wanna define it by a constant, and this is what the constant will be. Think about it nowadays. How often do we have
unanimity in anything we do. This was I think special. (upbeat music)