And it underpins biology.
Theory that atoms exist, i.e. matter is not continuous.
Much before atoms were thought to be "experimentally real", chemists from the 19th century already used "conceptual atoms" as units for the proportions observed in macroscopic chemical reactions, e.g. . The thing is, there was still the possibility that those proportions were made up of something continuous that for some reason could only combine in the given proportions, so the atoms could only be strictly consider calculatory devices pending further evidence.
Subtle is the Lord by Abraham Pais (1982) chapter 5 "The reality of molecules" has some good mentions. Notably, physicists generally came to believe in atoms earlier than chemists, because the phenomena they were most interested in, e.g. pressure in the ideal gas law, and then Maxwell-Boltzmann statistics just scream atoms more loudly than chemical reactions, as they saw that these phenomena could be explained to some degree by traditional mechanics of little balls.
Confusion around the probabilistic nature of the second law of thermodynamics was also used as a physical counterargument by some. Pais mentions that Wilhelm Ostwald notably argued that the time reversibility of classical mechanics + the second law being a fundamental law of physics (and not just probabilistic, which is the correct hypothesis as we now understand) must imply that atoms are not classic billiard balls, otherwise the second law could be broken.
Pais also mentions that a big "chemical" breakthrough was Isomers suggest that atoms exist.
Very direct evidence evidence:
- Brownian motion mathematical analysis in 1908. Brownian motion just makes it too clear that liquids cannot be continuous... if they were, there would obviously be no Brownian motion, full stop.
- X-ray crystallography: it sees crystal latices
- scanning tunnelling microscope: it sees individual atoms for Christ's sake, what else do you want?
Subtle is the Lord by Abraham Pais (1982) page 40 mentions several methods that Einstein used to "prove" that atoms were real. Perhaps the greatest argument of all is that several unrelated methods give the same estimates of atom size/mass:
- from 1905:
- in light quantum paper
- enabled by experimental work of Wilhelm Pfeffer on producing rigid membranes
- sugar molecules in water
- Brownian motion: investigations on the theory of the Brownian movement by Einstein (1905)
- 1911: blueness of the sky and critical opalescence
On Wikimedia Commons since it is now public domain in most countries: https://commons.wikimedia.org/w/index.php?title=File:Perrin,_Jean_-_Les_Atomes,_F%C3%A9lix_Alcan,_1913.djvu
Subtle is the Lord by Abraham Pais (1982) page 85:
However, it became increasingly difficult in chemical circles to deny the reality of molecules after 1874, the year in which Jacobus Henricus van't Hoff and Joseph Achille Le Bel independently explained the isomerism of certain organic substances in terms of stereochemical properties of carbon compounds.so it is quite cool to see that organic chemistry is one of the things that pushed atomic theory forward. Because when you start to observe that isomers has different characteristics, despite identical proportions of atoms, this is really hard to explain without talking about the relative positions of the atoms within molecules!
TODO: is there anything even more precise that points to atoms in stereoisomers besides just the "two isomers with different properties" thing?
Small microscopic visible particles move randomly around in water.
If water were continuous, this shouldn't happen. Therefore this serves as one important evidence of atomic theory.
The amount it moves also quantitatively matches with the expected properties of water and the floating particles, was was settled in 1905 by Einstein at: investigations on the theory of the Brownian movement by Einstein (1905).
This suggestion that Brownian motion comes from the movement of atoms had been made much before Einstein however, and passed tortuous discussions. Subtle is the Lord by Abraham Pais (1982) page 93 explains it well. There had already been infinite discussion on possible causes of those movements besides atomic theory, and many ideas were rejected as incompatible with observations:
Further investigations eliminated such causes as temperature gradients, mechanical disturbances, capillary actions, irradiation of the liquid (as long as the resulting temperature increase can be neglected), and the presence of convection currents within the liquid.The first suggestions of atomic theory were from the 1860s.
Tiny uniform plastic beads called "microbeads" are the preferred 2019 modern method of doing this: https://en.wikipedia.org/wiki/Microbead
This was one of the first major models that just said:
I give up, I can't tie this to classical physics in any way, let's just roll with it, OK?
They are not observe because they would violate the conservation of angular momentum.
TODO confirm year and paper, wikipedia points to: https://zenodo.org/record/1424309#.YoTQe3XMJhE
Cody's lab had a nice 5 video series on making it at home! But the United States Government asked him to take it down as suggested at Video "What's Been Going On With Cody'sLab? by Cody's lab (2019)" at https://youtu.be/x1mv0vwb08Y?t=84.
Here's a copy online as of 2020: https://www.youtube.com/watch?v=bCXB6BdMh9Y
Contrast with liquid nitrogen, which is much cheaper but only goes to 77K.
The layered one.
A single layer of graphite.
Trying to use gallium arsenide was Seymour Cray's fatal last flaw as mentioned at The Supermen: The Story of Seymour Cray by Charles J. Murray (1997).
The Supermen: The Story of Seymour Cray by Charles J. Murray (1997) page 4 mentions:
Cray wanted his new machine to employ circuits made from a material called gallium arsenide. Gallium arsenide had achieved limited success, particularly in satellite communications and military electronics. But no one had succeeded with it in anything so complicated as a computer. In the computer industry, engineers had developed a saying: "Gallium arsenide is the technology of the future," they would say. "And it always will be."
Another problem is that its half-life is long enough that it doesn't lose radioactivity very quickly compared to the life of a human person, although it is short enough to make it highly toxic, making it a terrible pollutant when released.
This is why for example in the goiânia accident a girl ended up ingesting Caesium-137 after eating an egg after touching the Caesium with her hands.
Not "Yt" because that is already "Yttrium". God.
There are no stable isotopes.
The least unstable isotope, occurs as part of the uranium 238 decay chain.
The definition does not include homonuclear molecules which is a pain.
Single chemical element, single phase (usually solid), but different 3D structures.
The prototypical examples are the allotropes of carbon.
The most important on in metabolism internals, everything else gets converted to it before being processed in the .
Nutrient that a given species cannot produce and must ingest in its diet.
https://en.wikipedia.org/w/index.php?title=Nutrient&oldid=1075972831#Essential gives somewhat of an overview:
Active compound in pepper.
https://iubmb.onlinelibrary.wiley.com/doi/full/10.1002/bmb.2002.494030030067 Surprises and revelations in biochemistry: 1950-2000 by Perry A. Frey (2006). This should be worth a read.
Ah, this seems like a nice dude.
Power, Sex, Suicide by Nick Lane (2006) paints a colorful picture of the man!
TODO why can't we produce organic compounds more cheaply by total synthesis than biosynthesis?
First, experiments, please how do you determine it and how it helps predict the future: https://chemistry.stackexchange.com/questions/42066/is-there-a-way-to-experimentally-measure-entropy
No YouTube video? Really?
- https://youtu.be/HQ1lrEQsj4c?t=51 shows Fluke 731B Voltage Standard which contains 1.018 values due to Weston cell voltage standard
I can't believe there isn't a YouTube video comparing various substances for each flammability and instability ratings, this would be a huge hit.