Placeholder Image

Subtitles section Play video

  • 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 concise, information-dense catalogue

  • of all of the different sorts of atoms in the Universe.

  • Today I want to talk a little bit about the creation of this table, which is, to be clear, one of the

  • crowning achievements of human thought. To start out, though, let's close our eyes and pretend.

  • [Intro music]

  • Imagine you're in Siberia. And you're a thirteen-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 re-opened an abandoned glassmaking factory

  • in the small town where you live, largely because she wants to make enough money to

  • send you to school someday. 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 it 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 1200 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

  • had graduated as a scientist, and as luck, or extreme, insane, undeniably Russian persistance would have it,

  • they accept you, and your saddle-worn butt, as a pupil.

  • Your mother, having completed her mission, promptly dies.

  • If you're doing your imagining as I told you, you might feel a tremendous debt to your mother,

  • and a very deep desire to ensure that you achieve something on par with the sacrifices she made for you.

  • And maybe that's one of the reasons why Dmitri Ivanovich Menedeleev became the crown jewel

  • of Russian science, and a theorist who revolutionized how we see the world.

  • Mendeleev spent a great deal of time in laboratories 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, we don't, yet - YET - but we're imagining.

  • So it's the 1860s, and about sixty elements are known to mankind,

  • and their atomic weights are mostly known as well.

  • So the simplest thing was to just sort them in order of their atomic weights.

  • But interestingly, you, because you're a cleverpants, realized that the most significant relationships

  • seem to have nothing to do with the atomic weight.

  • Lithium, sodium, potassium, and rubidium were all extremely prone to reacting with

  • chlorine, fluorine, iodine, and bromine; beryllim, 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.

  • On the side 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 repetition 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 names and weights and properties of elements on cards;

  • you lay them across your desk, shuffle 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.

  • 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,

  • eighteen-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. 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 Mendeleev, 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 atmosphere.

  • 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, seeing 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 with water, just a little more slowly,

  • producing a little less heat.

  • The middle body are of the table is made up of a nice, solid rectangle of transition medals -

  • these are the metals you think of as metals, with iron and nickel and gold and platinum.

  • The majority of elements 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 chemistry,

  • 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.

  • The rectangle between the halogens and the transition metals contain a peculiar scatter shot of metals,

  • 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 lanthanides and actinides,

  • metals that were largely undiscovered in Mendeleev's day because they're so similar

  • that it's next to impossible to seperate 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 scientist, 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 working on as a way to make some quick cash that he needed.

  • And, as with many other scientific revelations, there were a number of other people

  • hot on this discovery'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 better 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 consequences.

  • It seems as if he had a deep belief in the cosmic importance of what he was doing,

  • almost of religious fascination. Mendeleev believed in God, but also he believed that organized religions were

  • false paths 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 no 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.

  • But that form of the table is not by any means set in stone; indeed, a contemporary of Mendeleev evisioned

  • the table set onto a screw, or 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 Elements, and it was largely ignored.

  • I guess they didn't have paper craft back then, and 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 table 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 opposite sides on the map,

  • because they're just one proton away!

  • Mendeleev's contribution, nonetheless, is more powerful than at first it seemed.

  • He ended up forming 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 concerned with this stuff,

  • he actually denied the existence 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've 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.

  • This episode of Crash Course Chemistry was written by myself, filmed and directed by Caitlin Hofmeister,

  • and edited by Nick Jenkins. The script was edited by Blake de Pastino and Dr. Heiko Langner,

  • our sound designer is Michael Aranda, and Thought Café 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.