Hello Sir (I realise you have not given your name anywhere in the video or in the description below, or I may have missed it), Thanks for this excellent video. I studied chemistry in school and somehow the Avogadro's Constant - the idea that the same number of moles of any element should have the same number of atoms (if that is how one translates it) never made sense to me. It still doesn't and so turned to your video to see if I could get an answer. I must confess I haven't followed up on this and searched for answers in the interim, and so haven't been a good student. Can you please explain how the same volume of different gases (at same P and Temp) of the same mole (weight) have the same N, conceptually? I understand that the Ideal Gas Equation will give us that, but I was then trying to understand this in the following way: Imagine 1 mole of H2 gas is filled in a container of volume V (at some constant P and T) and weighed and it has N number of atoms (would calling them molecules be better?). If I fill that V (at same constant P and T) with 1 mole of another gas, say O2, and if it too has N number of atoms (molecules?) Now since the number of the atoms/molecules is same in both the cases, if I manage to "convert" (theoretically) the number of atoms of O2 into number of atoms of H2, wouldn't the number of nucleons (and so number of atoms) increase by the relative ratio of their atomic weights? Shouldn't N of Oxygen be more that N of H2 by their relative ratio of their atomic weights? Weren't the early chemists relying on measurements of P, V and weights (mass) to get these findings? So, why did they not think of the problem in this way? Why is N a constant for 1 mole of any element? Thank you. In case you do not have the time for a video, but can point me to some online resources that will throw some light on this, I would be grateful.
@@welingkartr416 "wouldn't the number of nucleons (and so number of atoms) increase by the relative ratio of their atomic weights?" I'm not sure whose misconception you're referring to here, so I'll assume you're talking about what's going on in the minds of the early chemists. We now know that if we could magically transform H2 into O2, the number of nucleons would change but the number of atoms would remain the same. The notion at the time, that more mass could mean more particles would have been a perfectly reasonable conjecture, but it was Avogadro and Loschmidt that drew the conclusion that this could not be the case based on the known gas laws. It was this insight that put weighing molecules (and from there calculating atomic weights) on a solid scientific footing. "Why is N a constant for 1 mole of any element?" Because N has now been defined as purely a number. You can use the Avogadro constant for counting anything you like, though it's only useful when you have truly enormous numbers of things (I wouldn't recommend it for counting eggs, for example). This video is about the history of how we came to choose that number rather than any other number. Have you watched my video on How and Why Chemists Use Moles?"
Wow, giving the chance to skip the video to people who might not have time for the whole thing. You are legendary my friend. Edit: I still watched the whole thing. Cool stuff man
Kathy Loves Physics Channel and you have provided much needed explanation of historical information that is not in common texts books. Thankfully, so, because in math and science subjects should teach the specifics, not the history. I always hated the name of any very obscure name and date being tossed into the middle of a math equation test.
Very nice video, thank you! One small mistake: it is true that Robert Brown was observing pollen when he saw the random motion of particles, but the grains themselves are way, way too large to wiggle in water. Rather, it was the dust that was formed when they were broken that did (he was looking at dried pollen from herbarium specimens). Brown at first though that the motion was of biological origin, but then experimented with other kinds of powders and found that they too wiggled in a similar way, so the phenomenon must have a more basic origin. Despite being a botanist, he realised the importance of his observation, and so published a very detailed account for physicists to consider. He wasn't even the first to see it, but was certainly the first who though it must hide something important.
@@davido3026I think only religious people of the past were against scientific community but if what you said is true then they can't be Freemasons they must be of some other cult. As far as I know these kind of cults are based on knowledge and experiments and there are many great scientists who were part of these philosophic groups. Do you have any evidence of your claim? Share it with the internet
@@Grateful92 Like there wasn't an absolutistic feudal system of oppression and arbitrary rule over centuries in place... **Facepalm** The only evidence we have here is that there is no doubt that this davido guy has not a small problem only with history and reality ... or that he is just one of those nutcases which are physically hurt by reading books and learning. They get their knowledge from the "X-Files" (for the older under us, hehe) or modern BS like Assassins Creep and Netflix fantasy stories. Don't waste your time. Kinds like these are only interesting in clinical psychiatric studies:) Oh and are you joking, too?:) "I think only religious people of the past were against scientific community" ... In what deep hole do you live? Don't you have newspapers? So you do know nothing about the 60% of American people doubting evolution theory (which is funny in itself as this is nothing you can doubt: It is something that describes OBSERVATIONS = Reality and tries to put those observations into a model we can predict something from ... like explanations why and how species exists. What comes tomorrow? We are doubting gravity ... or that the earth is round? ... wait a minute ... hehehehe) or fundamental christians killing women and doctors in front of abortion clinics ... because they want to "save lives". Oh and all the other absurd and horrific stuff all around the world that is done (RIGHT NOW!) in the name of their fantasy gods? Also: Science and the scientific community simply doesn't existed back then as you and I know it today. But to see all organized people like cult members or the people back then in general as fanatics or cult members is absurd. Not much differentiates them from us. They were loving and curious humans like we with no difference in the capacity of understanding and intelligence. NONE! To call such organizations a cult is equally stoopid as calling my chess club a political think tank. Only people who are allergic to learning (look something up...) and maybe have some mental conditions are subsceptible to see in everything behind the next corner something mystic, evil or who knows what. That is nothing we can solve here in the comment section of TH-cam. This can only be treated by an expert ... at least if there is some kind of self-awareness in the first place. In short: Not our problem!
Left school at age 15, am now 60. Great video and your style of presentation kept me captivated and curious enough to seek reference from Google to keep up as i watched watched. I was a person with only a passing interest in chemistry. I have now subscribed to your channel. Your excellent use of history sealed the deal. 👍👍👍👍👍
This is the best, most lucid presentation I’ve seen on anything in a very long time. Well researched and thought out, clear, simple, and brief. Style reminds me of James Burke’s ‘Connections’ series. Thank you for your work on this! Well done!
This was a blast. I was fascinated with Avogadro's story but seeing it intertwine with literally most of the concepts used in contemporary science is mindblowing. Loved it!!!
A few years ago I was taking a philosophy of science class to satisfy a breadth requirement for my degree in computer science. I ended up writing an essay on Jean Perrin's findings (which he published in a book, "Atoms"). What was remarkable was that he used something like half a dozen completely different experiments to estimate Avogadro's constant, and his calculated values were all surprisingly close to each other.
That's very cool. A better understanding of the history of science would I think go some way towards combatting the credulous acceptance of populists politics that is now making the world so unequal and dangerous.
Fascinating. When I was in high school chemistry in the late 50s, we were taught simply that there was this number, and that if you had that many atoms/molecules of something, you had a mole. End of discussion. And I never thought to look at the subject again. Now I'm glad I've seen your video, because I have a much better idea of how controversial, and important this number was.
Hey this is great. I did a much shorter video on Avogadro's Number, so I appreciate the deeper dive. I thought it was cool how you pointed out that Perrin formalized calling it Avogadro's Number, but it had been used in practice well before that. Didn't know that!
The history of science is full of those happy instances where some principles were used by intuition until someone else gave it a name, nothing wrong with that!! That way, the discovery was uniquely identified!
As a college student, I never imagined I would find a topic like this interesting when I was about to turn 76. Thank you for a great presentation. Yours truly,, A new subscriber
An astounding video. I've been learning chemistry for an ample seven years now and I've never been told the story behind the mole. Thank you for compiling and boiling all that information down, I can only wonder how much effort and time was put into creating it.
The nightmare of having to calculate the mass of elements starting from oxygen arbitrarily set to 100 makes me really wonder if some of the more difficult concepts in math and science are unnecessarily complicated by accurate but ridiculous models that work, but only a genius could grasp it.
Honestly, scientific notations seem complicated because thats a different language. Math notations are easier to read imo than physics or chem, because i am a stat math major. But, learning to read proofs is how you proceed with learning math. Its fun, just like learning a new language. All mathematical statements are proper sentences, with conjunctions between clauses. Just like you can't know every word in dictionary, but use words aming them, you can't arbitrarily read all math topic, but some. You get better at it with practice and time.
I mean, it's just a simple math problem... Especially if somebody that is educated like these guys were. But really those guys had to do routine and boring math like this. Spreadsheets sort of stuff.
Excellent video ! 10+++ It clears important milestones about how the number of Avogadro was calculated and, arguably astonishing enough, that it was not Avogadro who calculated the number, he only introduced the concept.
Thanks for the expansive explanation of these fundamental chemistry topics!!!! Cant wait for more. Pretty sure im going to watch every video you make! Curious: where did you learn chemistry? Really excited about learning it for myself and really glad to find people like you along my journey
Congratulations for this cristal clear presentation. I’ve finally understood what my science teacher tried in vain to explain 45 years ago. It’s never to late ! Thank you very much for helping us perceive the beauty of the scientific adventure.
As someone who was learning high school chemistry in the seventies. I was flabbergasted to learn that these issues that were dryly presented as settled science were still being debated in 1971. I also had no idea that the very existence of atoms and molecules was up for debate at the beginning of the 1900’s. I also have no idea what I was taught was the value of Avogadro’s number was but to discover it continued to change until a few years ago is really remarkable. Thank you for doing this video and I am so glad that I decided to click on this!
As another old-timer who took HS chemistry in the mid-70's I had exactly the same thoughts. When one is a teen I guess one tends to think of all past scientific progress as dead and dull.
This is the first time since the early 60s that I have encountered Avogadro’s number. I was astounded then and am astounded now to learn that it has changed.
I've always wondered how Avogadro's number was fixed, and your video gives the most comprehensive explanation I have ever heard about the subject. I recall being confused about the concept of gram-atom and gram-molecule and how they related to the mole, and your explanation cleared that mess up for me. When asked to produce Avogadro's number from memory, I immediately say 6.023 x 10^23 and then correct myself to 6.022 x 10^23. Probably says a lot about what the value was when I learned chemistry. I understand the ideas behind Brownian motion as supporting evidence for the existence of atoms, but I think that the development of atomic spectroscopy and mass spectometry are more convincing evidence for the existence of atoms and molecules. This was an excellent video with a very clear explanation of the development of a set of very fundamental concepts. Thank you for making and sharing it.
Thank you so much for this video. I kept wanting to find the source for the number and everything I read was either incomplete or wrong. Although, after this video I can see why. You gave such a complete and thorough explanation and easy to follow. Thank you once again.
As already noted in a commentary, Loschmidt is not mentioned. He gave in 1865 the first estimate of the number of Avogadro. Maxwell spoke about it and called it the Loschmidt constant. In Austria and Germany, the Avogadro number is also called the Loschmidt constant.
Very fascinating. You took me back to some 50 plus years ago when as a little country boy in St.Vincent I started reading chemistry by one named ?Bell. Its is remarkable that the methods used many many many hundreds of years ago and now are still in the 6 x 10^23. The subject is fascinating.Still a lover of Chemistry....Everything in the body depends on it! Bless you for such a great job! Big Thanks to you!
This is a crystal clear explanation of a concept that has always puzzled me. Moreover, I very much appreciate the "James Burke Style" of presentation walk-and-talk. Well done!
Amazing story. Thanks for telling it. What i found surprising is that many fundamental discovery's that make up modern chemistry are less then 100 years old.
I have a Degree in Physics and much more in EE, declining a PHD at Stanford in California but continuing at Berkley. I suffered in Chemistry in high school when the numbers changed, and it was still a bit mysterious. I very much enjoyed your presentation and talk. Thank you so much.
I have a degree in chemistry and this talk really nailed the events leading up to the mole standard that I have used so often. Thanks for giving us your time in such a fashion"
Love the clarity of thought and presentation and enunciation....was so correct one didn't have to strain to understand. Wonderful sense of history of chemistry. 🎉
i had been trying to understand the Avogadro's number and I was having difficulties truly understanding it until I viewed your video. My hat off to you ! Very well done! Thanks for helping me "remove this flee from my ear"!
Thank you so much for your excellent description of a common term and how it came to be. When I was in physics class in 1963 brownian motion was a hot item. In fact a professor from a large university came in with mystery and intrigue about brownian motion. We high school students soaked up this information. In the middle sixties in college we had more of an exact number, without all the decimal places for Avogadros number in college chemistry. We just knew the number was huge and exact. In my church a sermon presented how small atoms were. The preacher, (German), explained if you took a quart jar of a dye and poured it in the ocean, then let it mix through out the whole ocean, then scooped another quart of water 1,000 of those atoms would be in that quart jar. An example of Avogadros number.
I found your channel from this video. I have subscribed, but not yet browsed your other videos, yet. I did want to provide a thought for you. There is a gap in media in science programs for the general public and science programs for science people. This video is a great example. I compare and contrast to James Burke's Connection series. Compare: follow a thread throughout history on how a certain modern thing came to be. Contrast: His was meant for a general, albeit educated, audience. I am a theoretical mathematician by education, but working towards my Ph'D in Astrophysics. Missing from a lot of my education was the history behind a lot of this stuff. In a BA in Mathematics, my alma mater required a History of Mathematics course. As I got a BS, the course was not required. I would love to see someone fill that gap: Make Connections-like content detailing the history of something in science, but with the expectation that the audience already knows the science. What you have done in this video is closer to that than I have seen and I think you would do well with it.
Sir, you are a very organized teacher and a very clear communicator. It is obvious your presentation is the result of a great amount of time spent in careful effort, and involving much research into elements of the subject. My interest in your entire talk never flagged for an instant. You have requested comments and critiques, but I have only one contrary observation: I learned a long time ago, from more than a single source, I believe, that James Chadwick was credited with the discovery of the neutron in 1932, whereas you gave the year as 1937. (The date he was honored for that even preceded 1937.) Would you care to comment? Finally, thank you for this video. It was not only informative, but also quite entertaining!
Came here on the same thought, almost certainly he had to just misspeak the date. There was too much work with neutrons prior to 1937 by Fermi etc. for any other conclusion than this being slip of the tongue.
In high school the idea of a mole mystified me and it was not explained very well. Chemistry was just too confusing. Wish I had this little video at the time. Good work.
Really enjoyed this. The first time I learned about molar mass and atomic numbers, I was flabbergasted at how useful these concepts are for practical chemistry. I also enjoy history so this presentation hit me just right! I'm the type that sees The Voyage of the Beagle as an illumination of evolutionary theory.
Amazing! The value of Avogrado's number that I remember from high school chemistry in the 1970s is different than the modern value, and I never adjusted in my mind after years of college chemistry and chemical engineering!
never really understood avogadro #, mole, atomic weight, etc. thank you for the history and deep dive; also for speaking slow enough so that those of us not familiar with this don't get left behind
I graduated from high school in 1963 and went on to major in chemistry in college. My high school chemistry teacher, who was my inspiration, made us all memorize Avogadro's number and said when we came back for our 20th year reunion, she would ask us what the number was. And she did! The number she taught us in 1962-63 was 6.023x10e23rd. This is pretty far from the first number you give (7.1 x 10e23) but almost the same as the one you said was officially adopted in 1972 (or 73?) after compromises were made between physicists and chemists. I am certain (because of the challenge of my teacher) that the number a full decade before was almost exactly the number adopted 10 years later. Does that fit with your understanding of the timing of that value?
I also learned 6.023x10^23 in high school in the 80s, and I find it fascinating that it's now 6.022x10^23. I also see a quick Google search has the same now-wrong value. It's a shame the Wikipedia entry doesn't have the historical values for the constant in a nice table.
Excellent presentation, combining two of my favorite topics, science and history, but you had me wondering about halfway through whether you were approaching this from a chemistry or a physics perspective. Towards the end, it was revealed that I had intuited the right question, as that was the crux of the dilemma that had to be resolved.
I did think about getting into that, but I don't think it was a great deal more detailed than getting inspiration from trying to work out how the gas laws could possibly work. If you know of a detailed account somewhere, I'd love to see it.
You have really done your homework ! Outstanding summary of a complicated history . I wish I had seen this when I was doing 1st year Chemistry - it chewed away at me as to how they “ knew “ Hydrogen had an atomic weight of 1 - or whether it was a best guess - and it was !
That is a very well-crafted video and very informative. I am not a chemist. So it solidified a sketchy understanding of the subject - which is a lot more interesting than I ever expected. Well done. I hope you ended up wherever you were going.
Excellent explanation on Avogadro`s number i ever watched , it really helped me lot . I really appreciate your effort sir 👍😊😊. I really like this this kind of deep explanation on a single topic with simple language , keep it on .
Outstanding "explainer" video! It was actually quite enlightening for me, having last taken Chemistry in college in 1966, how *recent* much of this was.
oh lala....😂.....i didnt know that i wanted to know so much about all this actually, i was just seeing various explanations about the mole, cause i see that seeing various videos one gets it all. This was surprising, the walk was beautiful countryside, where is the way, i wish to walk it and the whole story all arround that topic was really so very nicly presented. if there is a very tiny little comment then i could say, for the jet slow speed of walking the voice sounded almost jet out of breath, of course talking while walking aint to easy but you could have walked even slower and you could have trained a little, sorry bout that, but the voice is so very most important in a video. big compliments from me! greetings from Gaby vienna.
Very good presentation of the notion of mole and Avogadro's Number as they evolved from the early crude perception and evolution to the current definition and accurate measurement by experiment through the contribution of so many chemists and other physicists!
Thank you for an excellent video! Avogadro's number is something that has been in the back of my mind since I left school - 62 years ago. I never quite understood how it could be worked out - I do now! (on to moles - another slightly grey area)
Ice video, I wish you had been my chem teacher at Guildford grammar school in 1962. My life may have turned out completely differently. 👍👍👍⭐️⭐️⭐️ from 🇦🇺
Excelent explanations. As your sugestion, I have a very difficult physical process (for me) to understand: what is the mechanics of force made with vacuum - like suspend a heavy sheet of glass. The typical "Force equals Pressure x Surface" doesn't apply (I think).
The Wikipedia explanation on "Magdeburg Hemispheres" is not satisfactory to me. Difference of pressures? Equalisation? I feel intermolecular forces are playing a big role. Well, if I am extracting molecules, the total force should be weaker ... but it becomes stronger!!! en.wikipedia.org/wiki/Magdeburg_hemispheres#Overview
Wonderful explanation professor! Your work on youtube is severely underrated and deserves more views! Please excuse my silly doubt as I am, now, only a highschool student. Avogadro's law says that "Under the same conditions of temperature and pressure, equal volumes of different gases contain an equal number of molecules." But how is that possible? Lets take Helium and Argon, for example... Argon is bigger than Helium, and hence one Argon molecule would take more volume than a Helium molecule right? So, then, how would they have the same number of molecules in the same volume? Again, thank you for the explanation!
I was familiar with most (but not all) of the characters, but you threaded them together in a convincing, understandable way that I haven't seen before - great job! I know you can't take the time to name all the players who contributed every little bit along the way, but I recently discovered one that I think would've been worth mentioning: Lucretius (~60BCE) observed Brownian motion in dust and used atomic theory to explain it. Check out the Wikipedia article on Brownian motion (that's not where I discovered it, but it gives context and a good summary). Lucretius was a remarkably insightful dude in a lotta ways.
What a superb presentation! I don't know how chemistry is taught in schools today but if it's anything like my chemistry lessons in the 1980s then this is something that would really help students who ask "...but WHY?" when something apparently arbitrary like the Mole is being taught. I laughed out loud at the part where an international body fixed the number at a certain value. It reminded me of Rupert Sheldrake discussing the gravitational constant.
A wonderful presentation which gives a clear view of the development of the science of Chemistry in a manner which links the elements and the Scientists in a memorable story. I hope current Science teachers watch this and learn how to present science in a manner that students will enjoy and remember. Well done! (I've subscribed of course!) I intend to watch this again and recommend it to my (teacher) friends. My introduction to Chemistry was in the late 1950's and it was taught simply as "many items to remember" (like King's names and dates etc) and I struggled with it. My best subjects were Maths & Physics so I ran with those. I was a little disappointed that you didn't mention the Russian chemist Dmitri Mendeleev, who put the 60 known elements into his periodic table in order of increasing relative atomic mass, in 1869. He would take umbrage when other Chemists actually found elements which fitted the spaces in his table which he left for them, claiming that "he" was the first to identify them.
Great TH-cam! Thank you. The most fascinating and painless science history lesson I've had the pleasure to experience!! Looking forward to your next youtube. PS. Was that somewhere in Africa where you were videoing? Loved the natural scenary.
9:12 Hey, at least here in Sweden, Jöns Jacob Berzelius is still a name in our textbooks! 😊 Particularly where I live, since the neighbouring city Linköpings is where he was an apothecary, which means there is still a school named after him. Also, I have my dad's old Handbook of Chemistry and Physics where oxygen-16 is the standard, and my maternal grandfather's book collection includes Berzelius' three-volume textbook on chemistry (printed in German), as my personal reminders of Jöns. . 😊
This was such an enjoyable video. It sounds like original research too, so could this be published that way ? I really enjoy your channel. The explanations are so clarifying. I am reminded of channels like Kathy loves physics and but why. I hope it's worth your time to do more. Is there a way like patreon to support you?
Brilliant. So many names, familiar and unfamiliar, making that classic tower of science. Thank you. A renowned plant breeder I know doesn't appreciate molecular botanists coming along and changing the 'family tree' of recognised names (a bit like the famous 'lumpers v splitters' discourse, makes things harder to remember etc). From now on I'll think of him as the chemist vs the physicists. You can't carry on denying the reality of measurement, just as he can't deny climate change by saying 'it's weather'.
One thing that blew my mind throughout this brilliant exposé was how LATE historically the current basic concepts of modern chemistry actually came to be. To think that Ostwald still thought that molecules didn't exist... But then I remembered why Mendelleev's periodic table came as such a shock to the community of chemists! That table was conceived way before an actual widespread and widely accepted notion of what an element was came to be. What was understood was there were relationships, quantitative ones, between "types of pure stuff", but nobody before Cannizzaro could come up and explain what was "hidden" begind those relationships. It is mind-boggling to try understanding how confused the whole picture must have been for 19th and early 20th century scientists without the luxury of knowing that elements are made of identical atoms in their purest, simplest forms, and that their weights actually come from the number of protons AND neutrons they contain, whereas the neutron was only discovered in 1937 - although its existence was predicted quite some time prior to its experimental demonstration.
Physicist here. Appreciate your video. Am always frustrated by Chemists who consider Avagadro constant to be a dimensionless physical constant. The actual physical constant is the mass of the proton, which has dimensions of mass. Up to tiny corrections, Avagadro’s number is just the inverse of this value in grams. The modern definition is arbitrary and defines the mol, but it was chosen basically to match this value.
Well, in the video, I briefly discuss how chemists and physicists have different interpretations of the mole because we use it for different purposes. The whole discussion actually goes much deeper, and is more interesting, than I had time for. There's a similar parting of ways with quantum mechanics of materials.
My chemistry + physics teacher mentioned another scientist, an Austrian man Josef Loschmidt, who came up with his own number of molecules in a certain volume, after calculating his estimate of the molecule size. He published it in 1865, being the first one to do so with a decent accuracy. Later on, he kept arguing with his friend Bolzmann about the molecules and gas behaviors, forcing Bolzmann to refine his theories and come up with the concept of entropy. I myself still cannot figure out the math involved in coming up with either the Loschmidt number or the Avogadro number, sigh...
The summary is at 32:06
Hello Sir (I realise you have not given your name anywhere in the video or in the description below, or I may have missed it),
Thanks for this excellent video. I studied chemistry in school and somehow the Avogadro's Constant - the idea that the same number of moles of any element should have the same number of atoms (if that is how one translates it) never made sense to me. It still doesn't and so turned to your video to see if I could get an answer.
I must confess I haven't followed up on this and searched for answers in the interim, and so haven't been a good student.
Can you please explain how the same volume of different gases (at same P and Temp) of the same mole (weight) have the same N, conceptually? I understand that the Ideal Gas Equation will give us that, but I was then trying to understand this in the following way:
Imagine 1 mole of H2 gas is filled in a container of volume V (at some constant P and T) and weighed and it has N number of atoms (would calling them molecules be better?).
If I fill that V (at same constant P and T) with 1 mole of another gas, say O2, and if it too has N number of atoms (molecules?)
Now since the number of the atoms/molecules is same in both the cases, if I manage to "convert" (theoretically) the number of atoms of O2 into number of atoms of H2, wouldn't the number of nucleons (and so number of atoms) increase by the relative ratio of their atomic weights?
Shouldn't N of Oxygen be more that N of H2 by their relative ratio of their atomic weights?
Weren't the early chemists relying on measurements of P, V and weights (mass) to get these findings? So, why did they not think of the problem in this way?
Why is N a constant for 1 mole of any element?
Thank you. In case you do not have the time for a video, but can point me to some online resources that will throw some light on this, I would be grateful.
@@welingkartr416 "wouldn't the number of nucleons (and so number of atoms) increase by the relative ratio of their atomic weights?"
I'm not sure whose misconception you're referring to here, so I'll assume you're talking about what's going on in the minds of the early chemists. We now know that if we could magically transform H2 into O2, the number of nucleons would change but the number of atoms would remain the same. The notion at the time, that more mass could mean more particles would have been a perfectly reasonable conjecture, but it was Avogadro and Loschmidt that drew the conclusion that this could not be the case based on the known gas laws. It was this insight that put weighing molecules (and from there calculating atomic weights) on a solid scientific footing.
"Why is N a constant for 1 mole of any element?"
Because N has now been defined as purely a number. You can use the Avogadro constant for counting anything you like, though it's only useful when you have truly enormous numbers of things (I wouldn't recommend it for counting eggs, for example). This video is about the history of how we came to choose that number rather than any other number. Have you watched my video on How and Why Chemists Use Moles?"
Wow, giving the chance to skip the video to people who might not have time for the whole thing. You are legendary my friend.
Edit: I still watched the whole thing. Cool stuff man
Kathy Loves Physics Channel and you have provided much needed explanation of historical information that is not in common texts books. Thankfully, so, because in math and science subjects should teach the specifics, not the history. I always hated the name of any very obscure name and date being tossed into the middle of a math equation test.
And miss the commentary from the peanut gallery at 5:52 ? Naaa...
As always, an excellent class that joins history, chemistry and a lot of information with a really clear oratory. Thanks for that!
Very nice video, thank you! One small mistake: it is true that Robert Brown was observing pollen when he saw the random motion of particles, but the grains themselves are way, way too large to wiggle in water. Rather, it was the dust that was formed when they were broken that did (he was looking at dried pollen from herbarium specimens). Brown at first though that the motion was of biological origin, but then experimented with other kinds of powders and found that they too wiggled in a similar way, so the phenomenon must have a more basic origin. Despite being a botanist, he realised the importance of his observation, and so published a very detailed account for physicists to consider. He wasn't even the first to see it, but was certainly the first who though it must hide something important.
Thanks for that!
Canizzaro
Gay Lussack,
Lavoisier, etc. (killed by the freemasonic French Revolution) chemistry development, history... brilliant! Thank you
I agree. But, s'il vous plait, Gay Lussac. No K. :)@@davido3026
@@davido3026I think only religious people of the past were against scientific community but if what you said is true then they can't be Freemasons they must be of some other cult. As far as I know these kind of cults are based on knowledge and experiments and there are many great scientists who were part of these philosophic groups.
Do you have any evidence of your claim?
Share it with the internet
@@Grateful92 Like there wasn't an absolutistic feudal system of oppression and arbitrary rule over centuries in place... **Facepalm**
The only evidence we have here is that there is no doubt that this davido guy has not a small problem only with history and reality ... or that he is just one of those nutcases which are physically hurt by reading books and learning. They get their knowledge from the "X-Files" (for the older under us, hehe) or modern BS like Assassins Creep and Netflix fantasy stories. Don't waste your time. Kinds like these are only interesting in clinical psychiatric studies:)
Oh and are you joking, too?:) "I think only religious people of the past were against scientific community" ... In what deep hole do you live? Don't you have newspapers? So you do know nothing about the 60% of American people doubting evolution theory (which is funny in itself as this is nothing you can doubt: It is something that describes OBSERVATIONS = Reality and tries to put those observations into a model we can predict something from ... like explanations why and how species exists. What comes tomorrow? We are doubting gravity ... or that the earth is round? ... wait a minute ... hehehehe) or fundamental christians killing women and doctors in front of abortion clinics ... because they want to "save lives". Oh and all the other absurd and horrific stuff all around the world that is done (RIGHT NOW!) in the name of their fantasy gods?
Also: Science and the scientific community simply doesn't existed back then as you and I know it today. But to see all organized people like cult members or the people back then in general as fanatics or cult members is absurd. Not much differentiates them from us. They were loving and curious humans like we with no difference in the capacity of understanding and intelligence. NONE! To call such organizations a cult is equally stoopid as calling my chess club a political think tank. Only people who are allergic to learning (look something up...) and maybe have some mental conditions are subsceptible to see in everything behind the next corner something mystic, evil or who knows what. That is nothing we can solve here in the comment section of TH-cam. This can only be treated by an expert ... at least if there is some kind of self-awareness in the first place. In short: Not our problem!
History, science, mathematics, and a nice walk too, what more could a video contain.
Left school at age 15, am now 60. Great video and your style of presentation kept me captivated and curious enough to seek reference from Google to keep up as i watched watched. I was a person with only a passing interest in chemistry. I have now subscribed to your channel. Your excellent use of history sealed the deal. 👍👍👍👍👍
My favorite high school class was chemistry and it was taught by the best teacher anyone could have. His name, Robert Frost.
Same. Jim Hackett, I'm 63 and will be always grateful even though I never 'needed' it. @@williamp9361
Totally agreed, this is great stuff!
This man just casually explains the history of Avogadro's number on a nice walk
Haha
You are an excellent communicator. Thanks for who you are and what you do.
This is the best, most lucid presentation I’ve seen on anything in a very long time. Well researched and thought out, clear, simple, and brief. Style reminds me of James Burke’s ‘Connections’ series.
Thank you for your work on this! Well done!
This was a blast. I was fascinated with Avogadro's story but seeing it intertwine with literally most of the concepts used in contemporary science is mindblowing. Loved it!!!
A few years ago I was taking a philosophy of science class to satisfy a breadth requirement for my degree in computer science. I ended up writing an essay on Jean Perrin's findings (which he published in a book, "Atoms"). What was remarkable was that he used something like half a dozen completely different experiments to estimate Avogadro's constant, and his calculated values were all surprisingly close to each other.
That's very cool. A better understanding of the history of science would I think go some way towards combatting the credulous acceptance of populists politics that is now making the world so unequal and dangerous.
this is the most amazing video about this topic that i have ever seen. thank you SO SO much for it! you're incredible!
And thank you so much for your lovely comment!
Fascinating. When I was in high school chemistry in the late 50s, we were taught simply that there was this number, and that if you had that many atoms/molecules of something, you had a mole. End of discussion. And I never thought to look at the subject again. Now I'm glad I've seen your video, because I have a much better idea of how controversial, and important this number was.
Really great and comprehensive summary. I think that Boltzmann probably deserved a mention but to be fair it’s already a pretty long video.
Hey this is great. I did a much shorter video on Avogadro's Number, so I appreciate the deeper dive. I thought it was cool how you pointed out that Perrin formalized calling it Avogadro's Number, but it had been used in practice well before that. Didn't know that!
Thanks! I'd only intended a ten minute video myself but I couldn't stop. 😄
@@ThreeTwentysix and it turned out great 😂
The history of science is full of those happy instances where some principles were used by intuition until someone else gave it a name, nothing wrong with that!! That way, the discovery was uniquely identified!
As a college student, I never imagined I would find a topic like this interesting when I was about to turn 76. Thank you for a great presentation.
Yours truly,,
A new subscriber
Same @@prapanthebachelorette6803
Fascinating video, I had no idea about the history behind L. Thanks for this.
Thanks. I literally thought it would only take 10 minutes when I started. 😄
An astounding video. I've been learning chemistry for an ample seven years now and I've never been told the story behind the mole. Thank you for compiling and boiling all that information down, I can only wonder how much effort and time was put into creating it.
The nightmare of having to calculate the mass of elements starting from oxygen arbitrarily set to 100 makes me really wonder if some of the more difficult concepts in math and science are unnecessarily complicated by accurate but ridiculous models that work, but only a genius could grasp it.
You just described intellectual property...😢
So much of software works that way.
Honestly, scientific notations seem complicated because thats a different language. Math notations are easier to read imo than physics or chem, because i am a stat math major. But, learning to read proofs is how you proceed with learning math. Its fun, just like learning a new language. All mathematical statements are proper sentences, with conjunctions between clauses. Just like you can't know every word in dictionary, but use words aming them, you can't arbitrarily read all math topic, but some. You get better at it with practice and time.
String theory says hi
I mean, it's just a simple math problem... Especially if somebody that is educated like these guys were. But really those guys had to do routine and boring math like this. Spreadsheets sort of stuff.
Excellent video ! 10+++ It clears important milestones about how the number of Avogadro was calculated and, arguably astonishing enough, that it was not Avogadro who calculated the number, he only introduced the concept.
Thanks for the expansive explanation of these fundamental chemistry topics!!!! Cant wait for more. Pretty sure im going to watch every video you make!
Curious: where did you learn chemistry? Really excited about learning it for myself and really glad to find people like you along my journey
Congratulations for this cristal clear presentation. I’ve finally understood what my science teacher tried in vain to explain 45 years ago. It’s never to late ! Thank you very much for helping us perceive the beauty of the scientific adventure.
As someone who was learning high school chemistry in the seventies. I was flabbergasted to learn that these issues that were dryly presented as settled science were still being debated in 1971. I also had no idea that the very existence of atoms and molecules was up for debate at the beginning of the 1900’s. I also have no idea what I was taught was the value of Avogadro’s number was but to discover it continued to change until a few years ago is really remarkable. Thank you for doing this video and I am so glad that I decided to click on this!
As another old-timer who took HS chemistry in the mid-70's I had exactly the same thoughts. When one is a teen I guess one tends to think of all past scientific progress as dead and dull.
This is the first time since the early 60s that I have encountered Avogadro’s number. I was astounded then and am astounded now to learn that it has changed.
I've always wondered how Avogadro's number was fixed, and your video gives the most comprehensive explanation I have ever heard about the subject. I recall being confused about the concept of gram-atom and gram-molecule and how they related to the mole, and your explanation cleared that mess up for me. When asked to produce Avogadro's number from memory, I immediately say 6.023 x 10^23 and then correct myself to 6.022 x 10^23. Probably says a lot about what the value was when I learned chemistry.
I understand the ideas behind Brownian motion as supporting evidence for the existence of atoms, but I think that the development of atomic spectroscopy and mass spectometry are more convincing evidence for the existence of atoms and molecules.
This was an excellent video with a very clear explanation of the development of a set of very fundamental concepts. Thank you for making and sharing it.
This video is a gem. I’ve been wondering about the history of Avogadro’s number for many years now…. And, now I have the answer. Thank you!
Thank you so much for this video. I kept wanting to find the source for the number and everything I read was either incomplete or wrong. Although, after this video I can see why. You gave such a complete and thorough explanation and easy to follow. Thank you once again.
I'm glad you enjoyed it!
As already noted in a commentary, Loschmidt is not mentioned. He gave in 1865 the first estimate of the number of Avogadro. Maxwell spoke about it and called it the Loschmidt constant. In Austria and Germany, the Avogadro number is also called the Loschmidt constant.
Very fascinating. You took me back to some 50 plus years ago when as a little country boy in St.Vincent I started reading chemistry by one named ?Bell. Its is remarkable that the methods used many many many hundreds of years ago and now are still in the 6 x 10^23. The subject is fascinating.Still a lover of Chemistry....Everything in the body depends on it! Bless you for such a great job! Big Thanks to you!
This is a crystal clear explanation of a concept that has always puzzled me. Moreover, I very much appreciate the "James Burke Style" of presentation walk-and-talk. Well done!
Thanks. You've taken me back more than half a century and given me a greater appreciation for chemistry and physics.
Amazing story. Thanks for telling it. What i found surprising is that many fundamental discovery's that make up modern chemistry are less then 100 years old.
That was damn good man!...
Simple and excellent 👍👍👍
I have a Degree in Physics and much more in EE, declining a PHD at Stanford in California but continuing at Berkley. I suffered in Chemistry in high school when the numbers changed, and it was still a bit mysterious. I very much enjoyed your presentation and talk. Thank you so much.
I have a degree in chemistry and this talk really nailed the events leading up to the mole standard that I have used so often. Thanks for giving us your time in such a fashion"
I wish chemistry was more accessible to "get your hands dirty". Amazing content, glad I've discovered your channel!
Love the clarity of thought and presentation and enunciation....was so correct one didn't have to strain to understand. Wonderful sense of history of chemistry. 🎉
I have no idea what youre on about here to start, but you hooked me with the intro. Fell into a learning hole again, learn me good.
i had been trying to understand the Avogadro's number and I was having difficulties truly understanding it until I viewed your video. My hat off to you ! Very well done! Thanks for helping me "remove this flee from my ear"!
Thank you so much for your excellent description of a common term and how it came to be. When I was in physics class in 1963 brownian motion was a hot item. In fact a professor from a large university came in with mystery and intrigue about brownian motion. We high school students soaked up this information. In the middle sixties in college we had more of an exact number, without all the decimal places for Avogadros number in college chemistry. We just knew the number was huge and exact. In my church a sermon presented how small atoms were. The preacher, (German), explained if you took a quart jar of a dye and poured it in the ocean, then let it mix through out the whole ocean, then scooped another quart of water 1,000 of those atoms would be in that quart jar. An example of Avogadros number.
I found your channel from this video. I have subscribed, but not yet browsed your other videos, yet. I did want to provide a thought for you. There is a gap in media in science programs for the general public and science programs for science people. This video is a great example. I compare and contrast to James Burke's Connection series. Compare: follow a thread throughout history on how a certain modern thing came to be. Contrast: His was meant for a general, albeit educated, audience. I am a theoretical mathematician by education, but working towards my Ph'D in Astrophysics. Missing from a lot of my education was the history behind a lot of this stuff. In a BA in Mathematics, my alma mater required a History of Mathematics course. As I got a BS, the course was not required.
I would love to see someone fill that gap: Make Connections-like content detailing the history of something in science, but with the expectation that the audience already knows the science. What you have done in this video is closer to that than I have seen and I think you would do well with it.
Sir, you are a very organized teacher and a very clear communicator. It is obvious your presentation is the result of a great amount of time spent in careful effort, and involving much research into elements of the subject. My interest in your entire talk never flagged for an instant. You have requested comments and critiques, but I have only one contrary observation: I learned a long time ago, from more than a single source, I believe, that James Chadwick was credited with the discovery of the neutron in 1932, whereas you gave the year as 1937. (The date he was honored for that even preceded 1937.) Would you care to comment? Finally, thank you for this video. It was not only informative, but also quite entertaining!
Came here on the same thought, almost certainly he had to just misspeak the date. There was too much work with neutrons prior to 1937 by Fermi etc. for any other conclusion than this being slip of the tongue.
In high school the idea of a mole mystified me and it was not explained very well. Chemistry was just too confusing. Wish I had this little video at the time. Good work.
Really enjoyed this. The first time I learned about molar mass and atomic numbers, I was flabbergasted at how useful these concepts are for practical chemistry. I also enjoy history so this presentation hit me just right! I'm the type that sees The Voyage of the Beagle as an illumination of evolutionary theory.
Amazing! The value of Avogrado's number that I remember from high school chemistry in the 1970s is different than the modern value, and I never adjusted in my mind after years of college chemistry and chemical engineering!
This is most interesting to me as a physicist. Thank you for putting all of this information together.
This is the best explanation of the origin and history of the Avogadro number that I have ever heard! Thank y-o-u-u-u
never really understood avogadro #, mole, atomic weight, etc. thank you for the history and deep dive; also for speaking slow enough so that those of us not familiar with this don't get left behind
I graduated from high school in 1963 and went on to major in chemistry in college. My high school chemistry teacher, who was my inspiration, made us all memorize Avogadro's number and said when we came back for our 20th year reunion, she would ask us what the number was. And she did! The number she taught us in 1962-63 was 6.023x10e23rd. This is pretty far from the first number you give (7.1 x 10e23) but almost the same as the one you said was officially adopted in 1972 (or 73?) after compromises were made between physicists and chemists. I am certain (because of the challenge of my teacher) that the number a full decade before was almost exactly the number adopted 10 years later. Does that fit with your understanding of the timing of that value?
I also learned 6.023x10^23 in high school in the 80s, and I find it fascinating that it's now 6.022x10^23. I also see a quick Google search has the same now-wrong value. It's a shame the Wikipedia entry doesn't have the historical values for the constant in a nice table.
I too was required to memorize 6.023X10e23 in high school in 1969. I still remember now.😃
I graduated in 2001 and I had to memorize 6.02 * 10 to the 23rd power I'm pretty sure I use that up until my second year of college chemistry.
I had the same requirement to memorize Avagadro's number in the mid 1980's, which was then given as 6.0225 x 10^23.
So your like what? 80 years old???
Excellent presentation, combining two of my favorite topics, science and history, but you had me wondering about halfway through whether you were approaching this from a chemistry or a physics perspective. Towards the end, it was revealed that I had intuited the right question, as that was the crux of the dilemma that had to be resolved.
Guy Lusacs experiments.
I think if you can include that in your video , would be great to see how Avogadro reached his theory
I did think about getting into that, but I don't think it was a great deal more detailed than getting inspiration from trying to work out how the gas laws could possibly work. If you know of a detailed account somewhere, I'd love to see it.
You have really done your homework ! Outstanding summary of a complicated history . I wish I had seen this when I was doing 1st year Chemistry - it chewed away at me as to how they “ knew “ Hydrogen had an atomic weight of 1 - or whether it was a best guess - and it was !
That is a very well-crafted video and very informative.
I am not a chemist. So it solidified a sketchy understanding of the subject - which is a lot more interesting than I ever expected.
Well done.
I hope you ended up wherever you were going.
I am enjoying your lecture, but would like to know where you are walking. It looks like a beautiful park. 🙏
Very well explained.
The surroundings and the science, wht a beautiful combination ❤. Excellent work
Excellent explanation on Avogadro`s number i ever watched , it really helped me lot . I really appreciate your effort sir 👍😊😊. I really like this this kind of deep explanation on a single topic with simple language , keep it on .
Outstanding "explainer" video! It was actually quite enlightening for me, having last taken Chemistry in college in 1966, how *recent* much of this was.
"It turned out to be a lot more complicated than I thought". Damm, you have me now.
oh lala....😂.....i didnt know that i wanted to know so much about all this actually, i was just seeing various explanations about the mole, cause i see that seeing various videos one gets it all. This was surprising, the walk was beautiful countryside, where is the way, i wish to walk it and the whole story all arround that topic was really so very nicly presented. if there is a very tiny little comment then i could say, for the jet slow speed of walking the voice sounded almost jet out of breath, of course talking while walking aint to easy but you could have walked even slower and you could have trained a little, sorry bout that, but the voice is so very most important in a video.
big compliments from me! greetings from Gaby vienna.
Very good presentation of the notion of mole and Avogadro's Number as they evolved from the early crude perception and evolution to the current definition and accurate measurement by experiment through the contribution of so many chemists and other physicists!
Thank you for an excellent video! Avogadro's number is something that has been in the back of my mind since I left school - 62 years ago. I never quite understood how it could be worked out - I do now! (on to moles - another slightly grey area)
Finally, all is revealed. Fantastic video.
I am not a chemist. I certainly enjoyed your clear narration of the story of this constant. And also the park that you were walking in !!
This is a great video, I've just added it to my favourite playlist.
Thx. I love these history lessons on science. Well done and insightful!
Just found your channel. Very impressed that you recorded this from memory (no notes?) and all fluidly.
Merci pour cette riche vidéo! Une promenade et un café en intelligence et pédagogie. J'ai gagné ma journée !
Fascinating!!! Thank you for that semi-scientific-historic review on top of your unique style.
this is a lecture that should be a precursor to reactions in high school.
Thanks for all the research you had to do on this topic.
Very informative! Thank you so much.
Excellent. I really enjoyed that.
Ice video, I wish you had been my chem teacher at Guildford grammar school in 1962. My life may have turned out completely differently. 👍👍👍⭐️⭐️⭐️ from 🇦🇺
Un gran repaso de lo que estudiamos de química y física desde secundaria hasta terminar nuestras carreras de ingeniería. Gracias!
Brilliant! Thank you, thank you x
I learned the Avogadro constant in 1974; it's funny how much the concept and number have changed over the years since then.
Thanks for the talk;
Excelent explanations. As your sugestion, I have a very difficult physical process (for me) to understand: what is the mechanics of force made with vacuum - like suspend a heavy sheet of glass. The typical "Force equals Pressure x Surface" doesn't apply (I think).
The Wikipedia explanation on "Magdeburg Hemispheres" is not satisfactory to me. Difference of pressures? Equalisation? I feel intermolecular forces are playing a big role. Well, if I am extracting molecules, the total force should be weaker ... but it becomes stronger!!! en.wikipedia.org/wiki/Magdeburg_hemispheres#Overview
There is no "Vacuum Force". It is the air pressure (not counteracted on the vacuum side).
Tremendous. This is what education needs. Well done my friend.
Wonderful explanation professor! Your work on youtube is severely underrated and deserves more views!
Please excuse my silly doubt as I am, now, only a highschool student.
Avogadro's law says that "Under the same conditions of temperature and pressure, equal volumes of different gases contain an equal number of molecules." But how is that possible?
Lets take Helium and Argon, for example... Argon is bigger than Helium, and hence one Argon molecule would take more volume than a Helium molecule right? So, then, how would they have the same number of molecules in the same volume?
Again, thank you for the explanation!
I was familiar with most (but not all) of the characters, but you threaded them together in a convincing, understandable way that I haven't seen before - great job!
I know you can't take the time to name all the players who contributed every little bit along the way, but I recently discovered one that I think would've been worth mentioning: Lucretius (~60BCE) observed Brownian motion in dust and used atomic theory to explain it. Check out the Wikipedia article on Brownian motion (that's not where I discovered it, but it gives context and a good summary). Lucretius was a remarkably insightful dude in a lotta ways.
Thank you for posting your video. I enjoyed the Educational history lesson.
Rock on.👍🇬🇧KCB.
Fantastic, fantastic recap of a fantastic story. You won another suscriber
Thank you very much for the Wonderful description of a very less taught fundamental topic in science.🙂
videos like this puts everything back into perspective. Nicely Done!!
What a superb presentation!
I don't know how chemistry is taught in schools today but if it's anything like my chemistry lessons in the 1980s then this is something that would really help students who ask "...but WHY?" when something apparently arbitrary like the Mole is being taught.
I laughed out loud at the part where an international body fixed the number at a certain value. It reminded me of Rupert Sheldrake discussing the gravitational constant.
A wonderful presentation which gives a clear view of the development of the science of Chemistry in a manner which links the elements and the Scientists in a memorable story. I hope current Science teachers watch this and learn how to present science in a manner that students will enjoy and remember. Well done! (I've subscribed of course!) I intend to watch this again and recommend it to my (teacher) friends. My introduction to Chemistry was in the late 1950's and it was taught simply as "many items to remember" (like King's names and dates etc) and I struggled with it. My best subjects were Maths & Physics so I ran with those. I was a little disappointed that you didn't mention the Russian chemist Dmitri Mendeleev, who put the 60 known elements into his periodic table in order of increasing relative atomic mass, in 1869. He would take umbrage when other Chemists actually found elements which fitted the spaces in his table which he left for them, claiming that "he" was the first to identify them.
Excellent video! You now have a new Geophysicist subscriber.
Great TH-cam! Thank you. The most fascinating and painless science history lesson I've had the pleasure to experience!! Looking forward to your next youtube. PS. Was that somewhere in Africa where you were videoing? Loved the natural scenary.
Great teaching of a fascinating history. Thank you.
9:12 Hey, at least here in Sweden, Jöns Jacob Berzelius is still a name in our textbooks! 😊
Particularly where I live, since the neighbouring city Linköpings is where he was an apothecary, which means there is still a school named after him. Also, I have my dad's old Handbook of Chemistry and Physics where oxygen-16 is the standard, and my maternal grandfather's book collection includes Berzelius' three-volume textbook on chemistry (printed in German), as my personal reminders of Jöns. . 😊
This was such an enjoyable video. It sounds like original research too, so could this be published that way ?
I really enjoy your channel. The explanations are so clarifying. I am reminded of channels like Kathy loves physics and but why. I hope it's worth your time to do more.
Is there a way like patreon to support you?
Thanks. And yes, I am looking into publishing it. I will sort out some form of support soonish so keep an eye out!
Thank you for an amazing explanation of the Avogadro number!
Brilliant. So many names, familiar and unfamiliar, making that classic tower of science. Thank you.
A renowned plant breeder I know doesn't appreciate molecular botanists coming along and changing the 'family tree' of recognised names (a bit like the famous 'lumpers v splitters' discourse, makes things harder to remember etc). From now on I'll think of him as the chemist vs the physicists. You can't carry on denying the reality of measurement, just as he can't deny climate change by saying 'it's weather'.
wow, depth of research & gr8 explanation
Thank you, I appreciate it!
A wonderful histiry lesson - which cleared up my understandung to go beyond my O level psss in 1969. Thank you.
Excellent video! Very informative, and you have a great communication style.
Thank you for speaking slow and vocalizing, becouse Im from spain and I could understand everything. Great video 😊
A wonderfull explanation of a complex issue
One thing that blew my mind throughout this brilliant exposé was how LATE historically the current basic concepts of modern chemistry actually came to be. To think that Ostwald still thought that molecules didn't exist... But then I remembered why Mendelleev's periodic table came as such a shock to the community of chemists! That table was conceived way before an actual widespread and widely accepted notion of what an element was came to be. What was understood was there were relationships, quantitative ones, between "types of pure stuff", but nobody before Cannizzaro could come up and explain what was "hidden" begind those relationships. It is mind-boggling to try understanding how confused the whole picture must have been for 19th and early 20th century scientists without the luxury of knowing that elements are made of identical atoms in their purest, simplest forms, and that their weights actually come from the number of protons AND neutrons they contain, whereas the neutron was only discovered in 1937 - although its existence was predicted quite some time prior to its experimental demonstration.
Physicist here. Appreciate your video. Am always frustrated by Chemists who consider Avagadro constant to be a dimensionless physical constant. The actual physical constant is the mass of the proton, which has dimensions of mass. Up to tiny corrections, Avagadro’s number is just the inverse of this value in grams. The modern definition is arbitrary and defines the mol, but it was chosen basically to match this value.
Well, in the video, I briefly discuss how chemists and physicists have different interpretations of the mole because we use it for different purposes. The whole discussion actually goes much deeper, and is more interesting, than I had time for. There's a similar parting of ways with quantum mechanics of materials.
Great lecture. Thanks.🙂
My chemistry + physics teacher mentioned another scientist, an Austrian man Josef Loschmidt, who came up with his own number of molecules in a certain volume, after calculating his estimate of the molecule size. He published it in 1865, being the first one to do so with a decent accuracy. Later on, he kept arguing with his friend Bolzmann about the molecules and gas behaviors, forcing Bolzmann to refine his theories and come up with the concept of entropy. I myself still cannot figure out the math involved in coming up with either the Loschmidt number or the Avogadro number, sigh...