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The periodic table is 150 years old this week (economist.com)
274 points by jkuria 53 days ago | hide | past | web | favorite | 45 comments

One of the most interesting controversies I've seen about periodic table schemes is the placement of helium. It usually sits above neon as a noble gas. However, not everyone agrees with that:

"Two things are surprising about Mendeleev’s classification of the chemical elements according to the Periodic Law,” Bent writes. “One is how much of the classification has not needed revision. The other is how long the scheme’s second element has been misplaced, above neon, despite Mendeleev’s Rule of Light-Element Distinctiveness; despite his statement that the Periodic System is about atoms, not simple substances; despite classification by atomic physics of helium atoms as s2 systems (not p6 systems); despite appearance of the Left-Step Periodic Table nearly eight [now over nine] decades ago; and despite numerous implications of the LSPT that require placement of helium above beryllium.”


How you view the placement of helium (and other more difficult elements) comes down to what you believe the table represents:

- empirically-derived reactive trends of elemental substances (in which case helium above neon makes much more sense); or

- a summary of theoretically-derived electronic configuration (in which case helium above beryllium makes perfect sense).

You can see aspects of both views in the modern canonical table. It's weird exceptional cases like this that can, among other things, make chemistry such a difficult (and fun) subject to learn.

The noble gases had yet to be discovered when Mendeleev started the periodic table. Actually, the original periodic table is quite inaccurate; that it works at all is largely a coincidence that the d block has 10 elements and that the lanthanides were generally unknown (so the screwing that the f block does wouldn't crop up).

Electronic configuration is already screwed up in the periodic table more than just helium; there are several elements that don't match the expected electronic configuration, particularly in the f block. The f block itself is really annoying to actually place in the table, since there's arguments to be made as to whether La/Ac belong in the d block or if Lu/Lr move there, or if you should just cram the entire block as being a group 3 element, or if you should do something just for the lanthanides but not the actinides, etc.

Why does electronic configuration put it above Beryllium? Helium has a full first shell of electrons, and other noble gases have their subsequent shells filled with electrons, this is why they all have their property of being more or less inert. The reactive trends of noble gases aren't "emperically derived" as you say but as a result of being extremely energetically stable due to having full electron orbital shells.

EDIT: Perhaps I misunderstood and you meant that its initial placement was due to empirical data. But for good theoretical reason it has remained where it is IMO.

Beryllium has 2 electrons and 6 holes in the last shell.

Neon has 8 electrons and 0 holes in the last shell.

Helium has 2 electrons and 0 holes in the last shell.

How do you align Helium, in the 2 electrons column over Beryllium or in the 0 holes column over Neon?

[I vote for aligning it over Neon.]

If the number of holes tells you more about the reactivity and properties of the element than the number of electrons in the outermost shell, then they should be arranged that way. AFAIK there is no theoretical mandate that the periodic table should be the way that it is, so just organize it in the way that makes sense while also providing maximum utility.

If it were not for the reactive trends, would there be much benefit in ordering the elements periodically?

I remember having a periodic table as a kid on which helium was present twice. Seems like a good compromise.

I’ve also seen ones with hydrogen placed twice, above lithium and above fluorine.

In reactions hydrogen likes to gain an electron like the halogens rather than lose one like the alkali metals.

It's things like this that should serve as good reminders just how young our "modern existence" is, how far we've come as a species in such a short time, and (potentially) how easy it could all slip away if we let it.

Maybe that's not the best way to put it, but I hope my point comes across anyhow...

Happy Birthday, Periodic Table. May you have 150+ more...

> reminder

Time https://www.youtube.com/watch?v=2XkV6IpV2Y0

Space https://www.youtube.com/watch?v=0fKBhvDjuy0

It's like asking a 2 year old to count way... way past 10

>Space https://www.youtube.com/watch?v=0fKBhvDjuy0

Made in 1977 and we can already comfortably go two orders of magnitude larger. Not bad.

(They should make a similar movie about wealth distribution, going from someone who makes 1 dollar a month up until Jeff Bezos.)

Look up dollar street by the same people who made gap minder. It’s a wonderfully simple look into the differences in wealth and living, which shows you things like “favorite thing” filtered along an axis of wealth.

A more modern soundtrack for ‘Powers of Ten’: https://youtube.com/watch?v=NvG-jqGsWSk

There are now attempts to create a "periodic table" for data structures. Such a table would allow you to predict variations of data structures and the behavior of such variants. You can see such an example in page 7 of the PDF below.


That's pretty interesting, I look forward to see what comes out of this! People often tend to conflate "computer science" with "professional software development" and I admit my first reaction was "so what? I routinely use just a small handful of data structures, do we really need something like this?" but seeing it visually laid out in an easily-digestible format is somehow inspiring. From a scientific perspective I can imagine discovering more advanced structures much like "missing" elements from the periodic table.

Are neural networks (for example from TensorFlow) considered data structures?

They store data, so maybe it would have been nice to mention them in the paper even if it's to put them out of scope for X reasons.

This is very nice! Allow me to make a post about it :)

I'm very interested to read this paper, but the grammar mistake in the first sentence of the first section doesn't bode well...

Is it the is/are issue?

Maybe they are using it as a mass noun or speaking specifically about the the phrase itself or the idea of data structures. Could stem from a cultural or ESOL reason.

I'm pretty under-educated on chemistry, but I read Asimov's _Search For The Elements_ a few years ago and loved it. It really demystified things.

In modern times it's easy for laymen to just wave our hands and say "yeah, we use fancy technology to do this stuff, which pretty much just treats it as magic. Asimov goes through the development of the periodic table and the discover of individual elements using classic technology.

Scanning tunneling microscope is still opaquely magic in my brain, but reading about discovering an element using technology I already understand makes even modern chemistry feel more in the realm of stuff I can get a solid grip on.

So I actually did a PhD in chemistry and just happen to work in software for reasons [0]. A thing that totally blows my mind about the periodic table and early materials chemistry is how it's in essence a derivation of "quantum mechanical" electronic structure.

One which was achieved through top-down "black box" debugging of nature on a scale too small for any human to see or touch!

[0] https://news.ycombinator.com/item?id=19266614

Highly recommend reading Oliver Sacks' Uncle Tungsten - his tale of growing up and discovering the beauty of the periodic table with his home chemistry set. Made me appreciate chemistry and the periodic table and Oliver Sacks so much more.

I think the coolest thing about the periodic table is that it's macroscopic evidence of the discrete, particle nature of atoms and the rest of the sub-atomic universe.

Quote from Mendeleev himself:

"I saw in a dream a table where all the elements fell into place as required. Awakening, I immediately wrote it down on a piece of paper."

This is fascinating to me -- Our brains continue working during our sleep on problems we think about during our day!

The structure of Benzene was famously conceived in the same way.

Here's a bunch of other interesting subsequent designs https://en.m.wikipedia.org/wiki/Alternative_periodic_tables

In the last fifty years or so, 15 elements have been added to the periodic table.

I went to a talk at Oak Ridge National Lab soon after the discovery of Ununseptium (element 117 that is now called Tennessine) and it was really interesting the international collaboration needed to make the discovery happen.

Basically, at Oak Ridge they produced radioactive isotopes with the appropriate number of neutrons and protons to match the theoretical ratio of the atom. Then, those isotopes needed to be shipped to Russia so they could be smashed together in a particle accelerator to briefly create the atom which we know existed from its specific decay and gamma ray emission.

But there was a lot of political hurdles in the way of shipping the isotopes to Russia in the first place, and it almost didn't happen because the isotopes were decaying while paperwork was floundering between state departments.

The accessible (no registration/subscription required) article:


One of the best documentaries I've seen on the subject is BBC's A Volatile History : https://youtu.be/g_2bo4abkPI

Mendeleevs Table

Hey, to celebrate this, everybody share your favorite "Periodic Table of X" where X is something that is absolutely not periodic at all!

Douglas Copeland had a couple in Shampoo Planet. I have never read the novel, but when the NY Times printed them I did have to explain what the joke was to a household member who either never had encountered or had entirely forgotten the periodic table.

Internet time-wasting periodic table (created with CSS Grid)


Periodic table of Pokémon

Periodic Table of AWS Services was a hit at the office.

Tom Lehrer made mention of the elements of the ancient world. If compiled into a periodic table of elements, it would be:

Earth, Air, Fire, & Water

Periodic Table of Adobe Products.

Not enough for a full table, but their icons are already basically formatted like elements.

The Periodic Table of Things Not On Any So-Called "Periodic Table of X".

Does it contain itself?

Periodic table of self?

Periodic Table of Periodic Tables

Periodic Table of Bitcoin

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