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The Periodic Table: Crash Course Chemistry #4
The Periodic Table: Crash Course Chemistry #4
Hank Green explains the origins of the periodic table and provides a simple way to look at its different areas, as well as some interesting facts about the shape, and possible alternatives.
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Key Ideas
As this video progresses, key ideas will be introduced to invoke discussion.
Think about the following questions as you watch the video
- What does it mean that a table is periodic?
- Why are each of these sections important?
- Why does Hank wrap the table around in a cylinder like that?
: 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 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.
: 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 graduated 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.
: 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 something
: 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 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, 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.
: Lithium, 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 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 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.
: 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 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 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 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 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 working 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 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 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.
: 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 elements.
: 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 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 have hated them.
: But you, you will have a healthy respect for them.
: After you learn all about them on the next episode
: ofCrash Course Chemistry.
: Thank you for watching this episode
: ofCrash 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 Hoffmeister,
: 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.
: 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 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.
: 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 graduated 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.
: 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 something
: 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 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, 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.
: Lithium, 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 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 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.
: 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 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 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 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 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 working 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 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 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.
: 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 elements.
: 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 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 have hated them.
: But you, you will have a healthy respect for them.
: After you learn all about them on the next episode
: ofCrash Course Chemistry.
: Thank you for watching this episode
: ofCrash 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 Hoffmeister,
: 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.