It's so cool that you cover every subject I'm currently studying. After every class I have, I watch your videos about it and they help me understand every detail even better
This video really helped me understand Bohr and Balmer series more...I was originally only here for Balmer and found this by mistake but I'm so glad I stayed for you to cover both models. You're brilliant! Best of luck to you and thank you, it really helped me for PChem!
My dude. I'm gonna tell you a little story. I won a scholarship to Taiwan as a military so it wasn't normal. I recieved 2 months of study for the language and then all the main courses like physics and chemistry were in chinese. You are my hero.
This is one of the best explanations ever and the best explanation of the bohr model ever! It connected all the topics together in a short and simple way and answered all my questions!
Did anyone else get the correct answer for the comprehension question but with the wrong exponent? I got lambda = -1.094 x 10^-44 meters My values for the variables were as follows: E = -1.816 x 10^-19 Joules c = 3 x 10^8 meters/second h = 6.626 x 10 ^ -34 Joules
why at 2:28 to 2:31 does the photon energy go from a negative to a positive? Is that because the electron is said to have lost energy so the negative shows this? Where as the number for the energy must be positive?
3:08 I play a game about exploring space, so my analogy is: Let's say you have a spacecraft orbiting at a certain distance from the center. You can raise the apoapsis however you want. To get a parabolic escape, you only need a finite amount of energy, after which you end up in a hyperbolic trajectory and have a 'speed at infinity.' Note: This is meant as an analogy and not an actual representation of what happens.
Great video linking physics to chemistry. One thing puzzles me, though. We learned in electron configuration that each electron has its own place in a shell, subshell and orbital. What if a photon bumps an electron residing in 1s to 3p, but 3p is already full. Does the displaced electron kick one of the electrons out of 3p? And what happens to 1s that has lost an electron?
There is an another direct method to find wavelength of a photon , Taking Rydberg's constant to be 109677cm^-1 So then a different way to solve this question would be 1/wavelength = - 109677(1/6^2 - 1/3^2) = 9139.75 That implies , wavelength = 1/9139.75 = 1.0941 X 10^-6 m
Really it's worth .... Saving time..You told everything in minimum time..You are genius..Thank you very much for uploading and sharing your knowledge.. YOU ARE THE BEST PROFESSOR IN THE WORLD..
@@karhukivi Thank you. I figured it out from another video. I just found the formula in Serway's book and there was no mention about the R having different measurement units.
isn't the finally answer of the wavelength in the example negative become E = -4.08 * 10^-19 so the wavelength will be -4.86 * 10^15..... I love your explanation thank you so much for your help ☺️❤️❤️👍
for the last exercise you made a mistake concerning the rydberg constant beacause firslty you are calculating the energy not the wave lenghth so you have to munchen there E0*Zeff V2 ,THEN AFTER when you calculate the wave lenghth you do the rydberg constant in the equation .
Professor Dave, I think 3:00 is slightly inaccurate. The energy needed to eject an electron is indeed finite (just take the limit as n approaches infinity in the Rydberg's equation), but the distance from the nucleus to the shell that corresponds to n = infinity is infinite, as given by the Bohr's radius: r = a_0 n^2 where n is the shell number. I think you just got mixed up, great video nonetheless.
3:45 gives an amazing example of the usefulness of this model. 3:50 reminds me why I hated school. Of course I ask that very comprehension question every time I look at the sky.
is there a good explanation for why the electron energy is negative? I assume we only use the absolute value when calculating the wavelength because in that case we are only looking at the change in energy (plus wavelength would be positive anyways). But what is the actual energy of the electron, and not the change in energy when it goes through a transition? I know it has something to do with that is really the energy it takes to remove the electron from the atom itself, so how do we mathematically put this together with the total energy in the system of the atom? Not entirely sure if this question makes sense.
Just one thing When he applied the rule How did the sign flip delta E was negative but wavelength couldnt be except positive. (I know im missing out on smthing so if somebody can point it out id be grateful)
I don't understand how you've got from the penultimate line to the last line. Surely putting in a negative value for E would give a negative value for l (although l has to be positive) as h and c are both positive?
wouldn’t n=infinity technically be impossible because of the plank length? Because at a certain point the gap between n’s would get so small it would reach the plank length. Or am I miss understanding something?
it's not so much that: the transitions to level 2 in hydrogen "just happen to fall in the visible spectrum" as it is that: our eyes evolved to detect those transitions (i'm guessing because the transitions to level one were too hard to handle)
Based on my understanding in this study of Bohr model of the hydrogen atom or a hydrogen-like ion where the negatively- charged electron confined to an atomic shell encircles a small, positively charged atomic nucleus and where an electron jumps between orbits it is accompanied by an emitted or absorbed amount of electromagnetic energy
Is Rydberg's constant -2.179x10^-18 OR 1.9737x10^7? The former was used in this video and the latter is what my textbook have... How many Rydberg constants are there?
This was really helpful. Thank you! One question: why does hydrogen have the series for n=2? Shouldn't it be n=1, since it's only got one electron? Why would it start at the second energy level?
but photons are emitted when an electron relaxes from an excited state to a lower state. it can go from 4 to 2, or 4 to 1, or 3 to 2, any transition is possible and will be accompanied by the emission of a photon of a particular wavelength that corresponds to the change in energy associated with that transition.
@@ProfessorDaveExplains Oh, so we're talking about photons being _emitted,_ not _absorbed!_ I don't know how I missed that, since I'm pretty sure you explicitly mentioned it in the video now that I think about it. 🤦 So is it just that every element has a single lowest energy level and that determines which frequencies and hence which wavelengths of light it emits? Although that still doesn't explain why hydrogen's lowest level would be 2 instead of 1. You said in your video on quantum numbers that the energy levels corresponds to the electron orbitals, yes? Hydrogen has only the single lowest orbital.
Going to the ground state (n=1 in this case) is called the Lyman series. Those energy transitions are observed in the very far-UV (122 nm and lower), whereas the Balmer series has energies in the UV and visible range of the spectrum.
Im having trouble with the conversions from energy to wavelength. why not just use v=E/h to get frequency and then c/v= to get wavelength? why does proffessor daves calculations show speed of light multiplied by planks constant over energy? please help.
At 1:43, you said delta E of electron = E of photon, but while doing the example (2:26) you said |delta E of electron| = E of photon. Can you or anybody else please explain the reasons for doing that way. Thanks
absolute value just makes sure there is no discrepancy in sign, since change in energy for electron can be positive or negative depending on whether absorption or emission occurs
I have this question which assumes to have an element that has one electron just like hydrogen but it has so many energy levels. So according to the energy associated with the removal of an electron, will this element emit more energy than hydrogen or what and why? Here is my line of thought, I was thinking it will emit less energy because of less attraction between the nucleus (assuming that an electron will be in the lergest energy level) and an electron but again if we are to remember properly since there is only one electron, it will be in the n=1 shell to acquire the lowest energy state. This is what confuses me, I don't know what to do or is it my opinion which is not ok. Your response will be highly appreciated 🙏.
For the checking comprehension what number did you use for the wavelength? Was it the number we found to be the Joules of energy? I get that H is planks constant and c is the speed of light
You can also understand it by thinking that-" del E is inversely proportional to the square of n " Del E~ 1/ n'² { n' is ( n final )² - ( n initial )²}
ah the million dollar question! so do this, check out my clips on waves and standing waves in the classical physics series. then, check out my clip on quantum mechanics in the modern physics series. then all shall be revealed!
It will always match. The electron releases energy (it releases a photon) and drops down the exact amount that it lost👍 That's at least how I understood it after the video. Hope this helps!
check out my tutorial on QM and the schrodinger equation in the modern physics playlist, electrons should be thought of as standing waves rather than particles, and this will make more sense!
The idea of appears and appears elsewhere seems very strange to me, in fact an empty gap. Where there are no explanations that at certain times the electron may simply have less mass and at other times simply having more mass.
...About, how high can these energy level numbers (n) reach before the escape level (n=infinity)? I would guess it's quite small due to the tiny size of an atom. Thanks for the most excellent science series!!!
I'm wondering about this too. I imagine that there aren't actually infinite energy levels, since it obviously does eventually get ejected, so I don't get what's meant my n=infinite. Is it maybe just a shorthand for "as it approaches a given atom's maximum energy level"? Damn good stuff though, I'm watching through a few of these videos.
I don't get it... If you have two electrons... One electrons drops a level, emits a photon. The other electron adsorbs the photon, get bumped a level... then drops a level, emits a photon, and the original electron absorbs the photon it originally emitted... At that point no energy is lost. That can't be!
why would the original electron re-absorb the photon? highly unlikely! it emits a photon to be absorbed by some other object. but also, don't forget the law of conservation of energy. if we look at the whole universe as a system, we should specifically expect that no energy be lost overall.
Hello professor! I have a question that I tried to figure out but couldn't. For an H atom electrons, their energy is described as -RH/n^2. (a) This means that the energy is _negative_ (which I thought was ok since electrons are negatively charged - _is it correct to think about it this way?_ ). (b) But then I saw that the higher the energy level is (where electrons are supposed to have more [negative] energy), the less energy is expressed in the said equation. In other words, the equation says _(I think)_ that the electron energy is inversely proportional to the energy level it is in. So (a) and (b) seem to be contradictory. I thought that maybe it is that the higher the energy level is, the _less negative_ the electron energy is so in a sense it would be higher (but it makes little sense to me). where am I mistaken there? Thank you again for all your help!
hmm, yes it is a little tricky quantitatively, i just like to think of it as an analogy to gravitational potential energy. the higher you lift something up off the ground, the more gravitational potential energy it has, or the potential to fall back to the earth, and so the farther you pull the electron from the nucleus (while still bound to the atom), the more electromagnetic potential energy it has, or the potential to be pulled back towards the nucleus. this is why a larger n value corresponds with a "higher energy". but i get tripped up with the math now and again too.
Thank you for replying professor! It's a challenge to me to understand some conceptual aspects of science. I think, however, it's because the more you learn the more you need to learn to understand it _(if that makes sense)_ . So thank you for your videos! I see you start from the beginning and are still concise. Something really good is that they have a logical order so one can build upon each other. Please keep it up!
What does the equation "E(electron) = -Rh/n^2" mean at 1:53? I assume it would mean the average energy per electron of that energy level, but there is a minus in front of Rh and i dont think the electrons would contain a negative amount of energy, so the minus sign must mean the equation means something else. Ive missed something, but i dont know what. Is it how much energy an electron needs to emit (minus sign, like in the video) or gain (plus sign) to leave the energy level(n)? So E = -Rh/3^2 = -2.42111111^-19 joule, would mean the electron's energy needs to change by -2.42111111^-19 joule to go from shell 3 to shell 2?
It means an electron at energy level "n" has an energy of E = Rh/n² , as for the " - " it's as you say : it's to say that that energy is required to get from energy level n to energy level n+i (you said "shell" but it's not "shell" , it's "energy level", one energy level can have multiple shells if i recall correctly). Meaning if you take E=Rh/n² it's the energy from energy level "n" to energy level "infinity" (out of atom)
