The Periodic Table: Crash Course Chemistry #4

Summary

In this episode of Crash Course Chemistry, Hank Green narrates the story of Dmitri Mendeleev, the creator of the periodic table, and his quest to organize the elements based on atomic weights and properties. Mendeleev's insight into the periodic nature of elements led him to predict the existence and properties of undiscovered elements. The video also touches on the periodic table's evolution, its various forms, and the significance of Mendeleev's work in shaping our understanding of chemistry.

Takeaways

• 🌟 Dmitri Mendeleev is credited with creating the periodic table, one of the most significant achievements in the history of science.
• 📚 Mendeleev's journey to create the periodic table was influenced by his family's struggles and his mother's sacrifices, which fueled his determination to succeed.
• 🧠 As a student, Mendeleev gained unique insights into the properties of elements, which later helped him in organizing them into the periodic table.
• 🔬 In the 1860s, about 60 elements were known, and Mendeleev noticed that their properties had a periodic relationship that was not strictly tied to atomic weights.
• 🃏 Mendeleev used cards to list and organize the elements' names, weights, and properties, eventually realizing that some elements were missing from the sequence.
• 🔮 He confidently inserted gaps for undiscovered elements and even predicted their properties, demonstrating a deep understanding of the periodicity of elements.
• 🤓 Mendeleev's periodic table was not immediately accepted, but his persistence and belief in the periodicity concept set him apart from his contemporaries.
• 🔄 The periodic table is organized into groups such as alkali metals, alkaline earth metals, transition metals, halogens, and noble gases, each with distinct properties.
• 🌐 The current form of the periodic table is not the only representation; alternative designs like the Periodic Cylinder of the Elements have been proposed.
• 🚀 Mendeleev's work laid the foundation for future discoveries in chemistry, including the understanding of electrons, which explain the periodicity of elements.
• 💡 The periodic table is a dynamic tool for understanding and categorizing the elements, and it continues to evolve with new scientific discoveries.

Q & A

Who is the host of the Crash Course Chemistry series mentioned in the script?

The host of the Crash Course Chemistry series is Hank Green.

What is the significance of the periodic table of elements in the context of the script?

The periodic table of elements is highlighted as one of the crowning achievements of human thought, providing a concise and information-dense catalog of all the different sorts of atoms in the universe.

What was Dmitri Ivanovich Mendeleev's initial challenge that led to his contribution to the periodic table?

Dmitri Ivanovich Mendeleev faced the challenge of his family's destitution after his father's death and his mother's efforts to support the family, which included moving him to Moscow and then St. Petersburg to get an education.

Why did Mendeleev's initial attempts to sort elements by atomic weights not fully capture their relationships?

Mendeleev realized that the most significant relationships between elements had nothing to do with their atomic weights, as elements with similar properties did not always have similar atomic weights.

What was Mendeleev's insight that led to the creation of the periodic table?

Mendeleev's insight was that there was a periodic relationship between atomic weights and the properties of elements, which led him to create the periodic table with gaps for undiscovered elements.

How did Mendeleev predict the properties of undiscovered elements?

Mendeleev predicted the properties of undiscovered elements by observing the patterns and trends in the properties of known elements and using these to deduce the properties of the missing elements that would complete the periodic table.

What was the outcome when a French scientist claimed to have discovered one of the elements Mendeleev predicted?

When the French scientist's data for the discovered element did not match Mendeleev's predictions, Mendeleev published a paper arguing that the French scientist's data was incorrect, and he turned out to be correct.

What are the characteristics of alkali metals as described in the script?

Alkali metals are soft, shiny, extremely reactive metals that readily lose an electron to form a positive ion or cation, and they are typically stored in inert gases or oil to prevent reaction with the atmosphere.

What is the significance of the transition metals in the periodic table?

Transition metals, which include iron, nickel, gold, and platinum, make up the middle body area of the periodic table and are characterized by being fairly unreactive, good conductors of heat and electricity, and malleable.

Why were the lanthanides and actinides initially difficult to discover and separate?

The lanthanides and actinides were difficult to discover and separate because they are very similar to each other, making it nearly impossible to distinguish between them without advanced techniques.

What was Mendeleev's attitude towards his periodic table after its initial publication?

Mendeleev was not satisfied with his periodic table and held it back for a while, only publishing it as part of a new chemistry textbook when he needed quick cash, indicating that he saw room for improvement.

What were some alternative visions for the periodic table mentioned in the script?

Some alternative visions for the periodic table included a screw or cylinder shape envisioned by de Chancourtois, and a circular form that would place elements with similar properties next to each other.

Outlines

00:00

🌟 The Inception of the Periodic Table

The script introduces the periodic table as a pivotal achievement in human thought, narrating the story of Dmitri Mendeleev's life and his journey to create the table. Born into a large family in Siberia, Mendeleev's father was a professor who went blind and passed away, leaving the family in poverty. His mother, determined to support the family and Mendeleev's education, moved them to Moscow and then to St. Petersburg, where he was accepted into a university despite initial rejections. Mendeleev's dedication and the sacrifices made by his family instilled in him a deep desire to succeed, which contributed to his groundbreaking work in chemistry. The script invites the audience to imagine being Mendeleev and to understand the significance of the periodic table's creation.

05:03

🔬 Mendeleev's Mastery and the Elements' Relationships

This paragraph delves into Mendeleev's meticulous work with the elements, his discovery of periodicity, and the development of the periodic table. Mendeleev observed that elements' properties repeated periodically, not strictly with atomic weights but in a pattern that emerged every seven elements. He was so confident in this periodicity that he left gaps in his table for undiscovered elements and even predicted their properties. His predictions were later confirmed when new elements were discovered, validating his theoretical framework. The script also discusses the different groups of elements as we understand them today, including alkali metals, alkaline earth metals, transition metals, halogens, and noble gases, highlighting their unique characteristics and reactions.

10:07

📚 Mendeleev's Legacy and the Evolution of the Periodic Table

The final paragraph reflects on Mendeleev's legacy and the periodic table's evolution. It acknowledges that while Mendeleev's table was revolutionary, it was not the only attempt to categorize elements, mentioning other scientists who were also exploring periodicity. Mendeleev's obsessive attention to detail and his belief in the broader implications of his work set him apart. The script also touches on the physical phenomenon behind periodicity, hinting at the role of electrons, which will be explored in future episodes. Additionally, it discusses alternative designs for the periodic table, suggesting that the current form is not perfect and could be improved for a more accurate representation of the elements' relationships.

Keywords

💡Periodic Table of Elements

The Periodic Table of Elements is a tabular arrangement of chemical elements, ordered by their atomic number, electron configuration, and recurring chemical properties. In the video, it is described as one of the crowning achievements of human thought, emphasizing its importance in understanding the universe's atomic composition. The script narrates how Dmitri Mendeleev's creation of the table revolutionized the field of chemistry.

💡Dmitri Mendeleev

Dmitri Ivanovich Mendeleev is a Russian chemist and inventor, best known for formulating the Periodic Law and creating a far-reaching version of the periodic table. The script tells the story of Mendeleev's life, his dedication to science, and how his insights led to the organization of the elements, showcasing his role as a key figure in the history of chemistry.

💡Atomic Weights

Atomic weights are the mass of an atom of an element, typically expressed in atomic mass units (amu). In the script, Mendeleev's initial approach to organizing elements was based on their atomic weights, which led him to discover the periodic nature of elements' properties, a fundamental concept in the periodic table.

💡Periodicity

Periodicity refers to the property of an element's characteristics repeating at regular intervals. The script explains how Mendeleev observed that elements' properties repeated periodically based on their atomic weights, which was a key insight in the development of the periodic table.

💡Alkali Metals

Alkali metals are a group of elements in the periodic table that are highly reactive due to their tendency to lose an electron and form a positive ion. The script describes their reactivity and how they are stored to prevent reaction with the atmosphere, illustrating the practical implications of their chemical properties.

💡Alkaline Earth Metals

Alkaline earth metals are another group in the periodic table, less reactive than alkali metals but still reactive enough to form cations with two positive charges. The script uses calcium as an example to compare its reaction with water to that of sodium, highlighting the similarities and differences among these elements.

💡Transition Metals

Transition metals are a block of elements found in the middle of the periodic table, known for their metallic properties such as conductivity and malleability. The script mentions iron, nickel, gold, and platinum as examples, emphasizing their importance and similarities within this group.

💡Halogens

Halogens are a group of non-metal elements that are highly reactive and form negative ions or anions. The script describes their reactivity and their tendency to react with alkali and alkaline earth metals, illustrating the periodic table's predictive power in chemical reactions.

💡Noble Gases

Noble gases are a group of elements characterized by their lack of reactivity due to their full valence electron shells. The script mentions that these elements were not discovered in Mendeleev's time, and their inclusion in the periodic table came later, showing the table's evolution and expansion.

💡Lanthanides and Actinides

Lanthanides and actinides are two series of elements with similar chemical properties that are usually placed at the bottom of the periodic table. The script points out that these elements were difficult to separate from each other, which is why they are treated as separate blocks in the modern periodic table.

💡Electrons

Electrons are subatomic particles that orbit the nucleus of an atom and are responsible for chemical bonding and reactivity. The script hints at the discovery of electrons as an answer to the 'Why?' questions posed by the scientific community after Mendeleev's work, indicating that the underlying physical phenomenon of periodicity is related to electron configurations.

Highlights

Introduction to the periodic table of elements as a significant catalog of atoms in the universe.

The story of Dmitri Mendeleev's challenging upbringing and his mother's sacrifices to support his education.

Mendeleev's unique insights into the properties of elements, gained from his time in laboratories.

The realization that elements' relationships are periodic, not strictly based on atomic weights.

Mendeleev's innovative method of using cards to organize and discover gaps in the periodic table.

Prediction of missing elements and their properties based on the periodic table's patterns.

Mendeleev's confidence in his theoretical framework, leading to a dispute over the discovery of a new element.

The description of different groups in the periodic table, including alkali metals and their reactivity.

Explanation of alkaline earth metals, transition metals, and their characteristics.

The role of halogens as reactive gases forming anions and their interactions with alkali and alkaline earth metals.

Mendeleev's belief in the cosmic importance of his work and his religious views on understanding the divine.

The physical phenomenon behind the periodicity of elements related to electron configurations.

Historical alternatives to Mendeleev's periodic table, such as the cylindrical model by de Chancourtois.

The current form of the periodic table and its limitations, including the separation of lanthanides and actinides.

Mendeleev's lasting impact on chemistry and the anticipation of future discoveries guided by his periodic table.

The acknowledgment of other scientists who contributed to the understanding of periodicity around the same time as Mendeleev.

The production credits for the Crash Course Chemistry episode, including the writer, director, and editors.

Transcripts

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 catalog 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.

[Theme 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 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 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 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 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, we don't, 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 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;

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.

On the side here, we now know that it's every eight elements,

but in the 1860s, elements were studies based on their reactivity,

so the non-reactive noble gases had not yet been discovered, so the period occurred every

As the mass of the elements increases, the repetition starts to get a little less periodic,

although 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 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 of 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.

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 area of the table is made up of a nice, solid rectangle of transition metals,

these are the metals you think of as metal, 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, 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.

1. 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 2. 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 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 - if 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 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 3D 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, it 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 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 form the scientific community was "Why? Why? Why?"

And although 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 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 in 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 designed 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 in Crash Course Chemistry.