2
BIG HISTORY PROJECT
0:34–1:41
LET’S PRETEND
1:42–2:32
DMITRI
MENDELEEV
0:00–0:34
PERIODIC TABLE OF
THE ELEMENTS
Hello, I’m Hank Green, welcome to Crash Course
Chemistry. Today we’re talking about the most
important table ever. Not the table where they
signed the Declaration of Independence, nor any
table of contents, nor this table right here, nor the
stone table of Aslan.
Nay, it is the periodic table of elements — a con-
cise, information-dense catalogue of all of the dif-
ferent sorts of atoms in the Universe.
Today I want to talk a bit about the creation of this
table, which is, to be clear, one of the crowning
achievements of human thought.
3.2
CHEMISTRY:
PERIODIC TABLE
OF ELEMENTS
To start out though, let’s close our eyes and pre-
tend. Imagine you’re in Siberia and you’re a 13-year-
old boy, and your father, who was a professor but
had gone blind, leaving your family of more than
ten brothers and sisters destitute, has just died. I
know, downer. Your mom, to support the family has
reopened an abandoned glass making factory in
the small town where you live largely because she
wants to make enough money to send you to school
some day. A year passes, the factory burns down.
But your mom, she sees your potential, she knows
that you have a keen scientific mind and will not
see that squandered. So with your siblings out of
the house and on their own, she packs up your
belongings, straps them to a horse, and with you in
tow, rides 1,200 miles through the Ural Mountains
on horseback to a university in Moscow. There, on
your behalf, she pleads earnestly and effectively
and they reject you.
So together, you ride another 400 miles to St.
Petersburg, to the school where your father gradu-
ated as a scientist, and as luck or extreme insane,
undeniably Russian persistence would have it,
they accept you and your saddle-worn butt as a
pupil. Your mother, having completed her mission,
promptly dies.
43 BIG HISTORY PROJECT
2:33–3:10
ATOMIC
WEIGHTS
If you’re doing your imagining as I’ve told you, you
might feel a tremendous debt to your mother and a
very deep desire to ensure that you achieve some-
thing on par with the sacrifices she made for you.
And maybe that’s one reason why Dmitri Ivanovich
Mendeleev became the crown jewel of Russian sci-
ence and a theorist who revolutionized how we see
the world.
Mendeleev spent a great deal of time in laborato-
ries as a student studying the burgeoning new field
of chemistry. He worked with all the elements that
you could work with at the time and his knowledge
gave him unique insights into their properties.
Those insights would come in handy.
Let’s all imagine we’re Mendeleev again — I like
doing that — and that we know a bunch of stuff
about chemistry, which you know, you don’t yet —
yet! But we’re imagining.
So it’s the 1860s and about 60 elements are known
to mankind and their atomic weights are mostly
known as well. So the simplest thing was just to sort
them in order of their atomic weights.
But interestingly, you, because you’re a clever pants,
realize that the most significant relationship seemed
to have nothing to do with the atomic weight. Lith-
ium, sodium, potassium and rubidium were all
extremely prone to reacting with chlorine, fluorine,
iodine, and bromine. Beryllium, magnesium, calcium
and strontium were all similar, but less reactive.
But with a quick inspection, you — and to be fair,
a number of other chemists — realize that there
was a relationship between atomic weights, but it’s
periodic. At the beginning of the list of elements,
characteristics repeat every seven elements.
An aside here, we now know that it’s every eight
elements, but in the 1860s, elements were studied
based on their reactivity, so the non-reactive noble
gases had not yet been discovered. So the period
occurred every seven elements.
As the mass of the elements increases, the repeti-
tion starts to look a little less periodic, though it’s
certainly still there. It just isn’t perfect. Some of
your colleagues, they’re saying, “Well, such is life.
“It was perfect repetition early on, but later in the
list it gets a little fuzzier.”
But not you. You become obsessed. Obsessed with
the perfection of the periodicity. You write out the
names and weights and properties of elements on
cards, you laid them across your desk, shuffled
them, tear them to pieces in frustration until one
day you realize that you’re simply missing cards.
The numbers aren’t working not because there’s
something wrong with your ideas, but because
some elements simply haven’t been discovered yet.
3:11–3:45
PERIODIC
RELATIONSHIPS
3:46–4:48
UNDISCOVERED
ELEMENTS
65 BIG HISTORY PROJECT
4:49–5:37
ALKALI METALS
Armed with this insight, you insert gaps into the
table and things suddenly fall perfectly into place.
Seven element periods for the first two rows with
hydrogen in its own category. 18-element periods
for the next two rows. You’re so certain, that you
predict the properties of these missing elements.
And when a French scientist comes along and
says that he has, in fact, discovered one of them,
you argue with him, saying that you discovered it
first in your mind. And when you see his data and it
doesn’t match yours, you publish a paper saying his
data for the new element he discovered is wrong.
That’s how certain you are of yourself and this
beautiful new theoretical framework you’ve created.
And you know what the really crazy thing is? You’re
right. That French guy’s data was wrong. You, never
having examined the element he discovered, knew
more about it than he did. Because you are Men-
deleev, master of the elements.
Okay, we’re done imagining for the episode. That
was fun though. The different groups Mendeleev
had identified are a lot of the same groups that we
study today. Starting at the left we have the soft,
shiny, extremely reactive alkali metals. So reactive,
in fact, that they have to be stored in inert gases
or oil to prevent them from reacting with the atmo-
sphere.
Alkali metals want nothing more than to dump off
an electron and form a positive ion or cation. And
they’re always jonesing to hook up with a hottie
from the other side of the table. So, of course, see-
ing as they’re so reactive, you don’t find hunks of
them lying around in nature.Instead, chemists must
extract them from compounds containing them.
Next you have the alkaline earth metals. Reactive
metals, but not as reactive as the alkali metals,
forming cations with two positive charges instead
of just one. Calcium, shown here undergoes a very
similar reaction to sodium in water, just a little
more slowly, producing a little less heat.
The middle body area of the table is made up of a
nice solid rectangle of transition metals. These are
the metals you think of as metals with iron, and
nickel, and gold, and platinum. The majority of ele-
ments are metals — they’re fairly unreactive, great
conductors of heat, but more importantly for us,
good conductors of electricity. They’re malleable
and can be bent, and formed, and hammered into
sheets. And they’re extremely important in chem-
istry, but overall surprisingly similar to each other.
On the far right, just over from the noble gases, the
halogens make up a set of extremely reactive gases
that form negative ions or anions with one negative
charge and love to react with the alkali and alkaline
earth metals.
5:38–6:19
ALKALINE EARTH
METALS
6:20–6:50
HALOGENS
87 BIG HISTORY PROJECT
6:51–7:30
LATHANIDES AND
NOBLE GASES
7:30–8:27
MENDELEEV
IS DIFFERENT
8:28–9:22
THE FORMS
OF THE TABLE
The rectangle between the halogens and the transi-
tion metals contain a peculiar scatter shot of met-
als, metalloids, gases and nonmetals. These guys
don’t end up as ions unless you take extreme action
and start shooting other ions at them. So generally,
a bit boring over here, though lots of interesting
covalent organic chemistry, we’ll get to that.
Down below in their own little island are the lan-
thanides and actinides — metals that were largely
undiscovered in Mendeleev’s day because they’re
so similar that it’s next to impossible to separate
them from each other.
And finally, on the far, far right, also undiscovered
when Mendeleev built his chart, the completely
unreactive noble gases.
Like a lot of other obsessive scientists, Mendeleev
never thought he was done with his table. So he
held it back for quite a while, only publishing it as
part of a new chemistry textbook he was work-
ing on as a way to make some quick cash that he
needed.
And as with many other scientific revelations, they
were a number of other people hot on this discov-
ery’s trail. As many as six people published on the
periodicity of elements at roughly the same time as
Mendeleev. But a few things set him apart.
One: he was obsessive. He knew the data bet-
ter than anyone else, and had spent a ton of time
working on a theory that many people thought was
just an interesting little quirk.
And two: he realized in a way no one else did, that
the idea of periodicity had far-reaching conse-
quences. It seems as if he had a deep belief in the
cosmic importance of what he was doing, almost a
religious fascination.
Mendeleev believed in God, but also he believed
that organized religions were a false path to the
unknowable nature of God. I like to believe that he
thought he saw some divine pattern in his tables
and Mendeleev felt as if he was coming to know
God in a way that no other man ever had.
To be clear, this is pure conjecture.
And as we now know the periodicity of elements is
a physical phenomenon. It’s a function of electrons,
which are, in some ways, pretty dang peculiar, but
certainly not at all mystical. But we’ll get to that
peculiar physical reality in the next episode.
The periodic table that we know and love — I love
it anyway — is a representation of reality, a way of
understanding and sorting the Universe as it exists.
109 BIG HISTORY PROJECT
9:25–9:44
LANTHANIDES AND
ACTINIDES
But that form of the table is not by any means set
in stone. Indeed, a contemporary of Mendeleev
envisioned the table sat onto a screw or a cylinder
with the elements wrapping around from one side
to another. While Mendeleev’s table looks more like
a map up on a wall, de Chancourtois, a geologist,
envisioned more of a globe. Unfortunately for de
Chancourtois, no publisher could figure out how
to print his cylindrical, three-dimensional table.
And so he published his paper without a graphical
representation of his periodic cylinder of the ele-
ments. And it was largely ignored.
I guess they didn’t have paper craft back then.
I am a huge fan of this cut and tape model of the
periodic table. You can make your own, there’s a
link in the description, and there are also a ton of
other designs for periodic tables that have various
advantages over the one that we’re all familiar with.
Our periodic table as it stands is really a little bit
unhappy with itself, frankly. The lanthanides and
actinides really should be part of the table, but we
separate them out because it’s hard to fit that on a
piece of paper.
Really, this is what it should look like.
And really, it would be best if it wrapped around
into a circle so that fluorine and neon and sodium
were all next to each other instead of being on the
opposite sides of the map because they’re just one
proton away.
Mendeleev’s contribution, nonetheless, is more
powerful than at first it seemed. He ended up form-
ing a guide to help future chemists understand
things that wouldn’t be discovered for 25, 50, even
100 years.
Indeed, after Mendeleev’s theories were published
and accepted, the overwhelming cry from the
scientific community was, “Why? “Why? Why?”
And though Mendeleev was not himself con-
cerned with this stuff, he actually denied the exis-
tence of atoms, or indeed anything he couldn’t see
with his own eyes. It turned out that the answer
to the first why was the electron.
That sneaky, little electron. Mendeleev, if he’d been
around to see their discovery, he would have hated
them. But you, you will have a healthy respect for
them. After you learn all about them on the next
episode of Crash Course Chemistry.
Thank you for watching this episode of Crash
Course Chemistry. If you were paying attention,
you now know the terrible, beautiful and wonderful
story of Dmitri Mendeleev, how he organized the
elements into the periodic table, some of the basics
of the relationships on that table, why Mendeleev
stood out from his colleagues, and how the table as
we know it today could stand some improvement.
9:45–9:56
MENDELEEV’S
CONTRIBUTION
9:57–10:30
ELECTRONS
10:31–11:21
CONCLUSION
1211 BIG HISTORY PROJECT
This episode of Crash Course Chemistry was writ-
ten by myself, filmed and directed by Caitlin Hoff-
meister, and edited by Nick Jenkins. The script was
edited by Blake de Pastino and Dr. Heiko Langner.
Our sound designer is Michael Aronda, and Thought
Cafe is our graphics team. If you have any questions,
please ask them in the comments below.
Thank you for learning with us here at Crash
Course Chemistry.