The periodic table is 150 years old this week
economist.com
economist.com
"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.”
https://cen.acs.org/unassigned/Reactions/97/i3
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.
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.
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.]
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.
In reactions hydrogen likes to gain an electron like the halogens rather than lose one like the alkali metals.
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...
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
Made in 1977 and we can already comfortably go two orders of magnitude larger. Not bad.
https://stratos.seas.harvard.edu/files/stratos/files/periodi...
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.
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.
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.
One which was achieved through top-down "black box" debugging of nature on a scale too small for any human to see or touch!
"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!
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.
https://www.newscientist.com/article/mg24132190-300-the-true...
Not enough for a full table, but their icons are already basically formatted like elements.
Earth, Air, Fire, & Water