The Quantum Mechanical model of an atom. What do atoms look like? Why?

once in a while a great scientist comes along who notices a pattern in nature that others may have completely missed for example isaac newton realized that the forces acting on a fired cannonball are the same as that on the moon orbiting the earth ernest rutherford was another such person when he realized that atoms have a heavy nucleus he hypothesized that the way the moon orbits the earth is the same as the way the electron orbits the nucleus of atoms newton was right rutherford we now know was wrong an atom would not look anything like this yet we still use the rutherford model to depict the way atoms look it's the most familiar image we have of the atom a real atom would look shockingly different from anything like this and it would definitely not be mostly empty space as you have been told what does an atom actually look like and how did we determine that why doesn't an electron just fall to the nucleus since they attract each other so strongly why can't we squeeze atoms together the answer requires us to look deeper into the meaning of quantum mechanics why do we trust quantum mechanics anyway and how did we arrive at this revelation perhaps the most accurate and proven theory in science the answer is coming up right now in 1911 ernest rutherford proposed a planetary model of the atom according to the model the solar system and the atom were almost identical just like the moon is held in orbit around the earth due to gravity the negatively charged electron was held in orbit around a positively charged nucleus the attractive force was electromagnetism instead of gravity in the case of the atom this seemed to make sense because isaac newton's laws of universal gravitation was almost identical to coulomb's law for electric force this was beautiful a fantastic symmetry of nature but alas it was too good to be true one big problem is that when electrons are accelerated as they would be when constantly changing direction traveling in circular orbits they create electromagnetic waves according to maxwell's equations this means that photons would be constantly radiated from the electron causing it to lose energy it would radiate a rainbow of colors getting bluer and more purplish as the electron came closer and closer to the nucleus until it collapsed into it so using classical laws for the atom did not work if you presumed the rutherford model a bold new step was needed but little did rutherford realize that 11 years earlier in 1900 max planck had already made this step by showing that energy of photons was quantized planck's theory had shown that matter emitted only discrete amounts of radiation with energy e proportional to the frequency f the proportionality constant h being planck's constant a young scientist by the name of niels bohr came along and combined rutherford's model and planck's theory to hypothesize that the electron could exist in certain special orbits without radiating energy how did he come up with this well what bohr noticed is that planck's constant had units of angular momentum so he hypothesized that only those orbits would be allowed where the angular momentum of the electron is quantized based on planck's constant and he guessed that the lowest orbit would have the momentum of h over 2 pi where the 2 pi comes from the geometry of circular orbits and any orbit could exist as long as it was an integer multiple of this number so the next orbit would be two times h over two pi and then three times for the next one and so on and bohr predicted that the electrons would only radiate or absorb energy when these electrons jumped from one orbit to another but bohr could not explain why electrons would not emit photons all the time or why these special orbits should exist in the first place but presuming he was right you could find the size of the orbit of the electron using coulomb's law it turns out that the radius at the lowest orbit would be 0.529 times 10 to the negative 10 meters about half an angstrom so now we knew the size of the atom which had been a mystery in the past knowing this the energy emitted by the electron as it changes orbits could be calculated and lo and behold observations from energy emissions confirmed these calculations so bohr's model was right since this model predicted values that could be verified it was thought that this was it this must be what atoms really looked like the problem was nobody knew why boar was right so this was probably not the final answer then along came a brilliant french scientist by the name of louis de bruy he said look if a particle has a momentum and it has a wavelength associated with it because of planck's constant then an electron is probably a wave this required a huge philosophical leap because here was a guy suggesting that solid matter things that we can see and feel on a macro scale was composed of waves matter was somehow a particle and wave at the same time de bruy suggested that electrons can only exist in orbits where their waves interfere constructively and that can only happen if the circumference of the orbit is equal to the wavelength or twice the wavelength or three times the wavelength or any integer times a wavelength this made sense and explained why orbits would be at the radii that they are something that bore could not do the bohr model was looking more and more legit but there were still many questions what is the nature of these waves and how and why do they exist a crucial piece of the puzzle was solved by austrian physicist irwin schrodinger he said look guys if it's a wave it can exist anywhere in three-dimensional space and he formulated the rules to describe the behavior of these waves the rules are encompassed in the schrodinger equation which became arguably the most important equation in quantum mechanics the rules were so spectacularly successful in making predictions that no one could really dispute it schrodinger's equation could describe the hydrogen atom with more detail and precision than the bohr model but it could also describe all the other atoms in the periodic table which the bohr model could not it was truly a revelation this was not newtonian mechanics anymore but a new kind of mechanics based on the quantum revolution started by max planck it was quantum mechanics and schrodinger's equation containing the wave function of atoms is the one critical piece of information that we need to determine what an atom most likely actually looks like but why do we even have to guess why don't we just settle the debate by just looking inside any material to see what these pesky little things actually look like the problem is that in order to be seen the object has to be large enough to reflect light but the largest atom is a thousand times smaller than the wavelength of visible light so visible light goes right through the atoms it can't really be seen because no light is reflected back what about using shorter wavelength light like x-rays the problem is that short wavelength light carries so much energy that it interacts with the electron changing it this is one of the consequences of the heisenberg uncertainty principle which says that the range of an electron's position times the range of its momentum cannot be below a certain constant h over four pi we cannot say where the electrons are or how fast they're moving at the same time so we can't draw a picture with a little electron in one place sitting on a circular orbit so we have to take our best guess based on what the wave equation tells us and what it tells us is that the electron forms a cloud around the nucleus the shape of the cloud is governed by the wave function it's called a wave function because the quantum wave equation resembles the equation for a classical wave the cloud represents the probable position of the electron if you were to measure it and this cloud exists everywhere from the nucleus to very far away from the nucleus the volume of the atom is thus definitely not empty it's filled everywhere with a cloud of electrons we can use the schrodinger wave equation to find the electron probability this plot shows the probability of finding the electron at various distances from the nucleus of a hydrogen atom the highest probability occurs at wouldn't you know it 0.529 times 10 to the negative 10 meters which is exactly the radius calculated by bohr so the most probable radius obtained from quantum mechanics is identical to the radius calculated by classical mechanics in bohr's model however the electron was assumed to be at this distance all the time whereas in the schrodinger model it is at this distance only some of the time it has the highest probability of being at this radius but it could be elsewhere too the difference is due to the heisenberg uncertainty principle and the fact that the electron acts like a 3d wave and the same wave equation tells us that the nucleus of atoms which in the case of the hydrogen atom is a proton is also a cloud but the extent of the proton cloud is much smaller than the electron cloud because it is much more massive so if you look at the uncertainty equation you can see that the extent of the delta x would be much smaller given a large m in order to satisfy the inequality the proton cloud is so small in fact that if the electron cloud was the size of michigan stadium the largest sports stadium in america which seats about 110 000 people the proton would be the size of a marble at the 50-yard line the electron cloud is about a hundred thousand times larger than the proton cloud so the idea of discrete spherical protons and neutrons in the nucleus or electrons orbiting them is really fiction it's good for showing kids in classrooms but not for students of quantum mechanics let me clarify though that you would never actually see a hydrogen atom in this state because the act of seeing it would necessarily change it but if by some magic you could see its state without measuring it this is a good approximation note that there are other shapes that the cloud of the hydrogen atom could take as well depending on the energy level and the quantum state of the electron but here are actual images of a hydrogen atom taken by an international team of researchers in 2013 so this is definitive proof that our 3d model is likely correct now given what i just said how can a photograph like this be taken well this is not a direct image if you read the paper you'll find that it's a composite image based on the trajectory of electrons emitted by hundreds of hydrogen atoms after they're excited by lasers so now we can answer original two questions first why doesn't the electron just fall to the proton in the nucleus if it is attracted to it after all if you drop a meteor directly onto the earth with no angular momentum it will hit the earth with a colossal amount of energy enough to kill all the dinosaurs like 65 million years ago but when it comes to the atom even if you dropped an electron with no angular momentum directly onto a proton the electron will not fall and hit the proton why because if it did it would violate the heisenberg uncertainty principle because both delta x and delta p in the equation would be zero and that can't be what happens is there will always be a balance between the position and momentum of the electron such that the uncertainty principle is obeyed what happens is the electron forms a cloud around the proton even if you dropped it you might say okay i get that but if it's a cloud why can't i squeeze two atoms together we have to go to a chart which shows the energy electron as a function of distance from the nucleus the electron prefers to be in the lowest energy state which is at a distance of 0.529 times 10 to the negative 10 meters from the nucleus in order to squeeze atoms to a smaller size we have to increase the energy of the electron this requires the electron to go to a higher energy state when you consider that there are quadrillions of atoms in any object that we can see for example a grain of sand has about 10 to the 18 atoms the cumulative amount of energy is humongous squeezing two objects together requires energies on the order of a small atomic bomb and this is the reason we have solid objects that we can hold in our hand without our hand being able to squeeze them to nothing and why we don't sink when we stand on solid ground so while quantum mechanics results in some very mysterious phenomenon that we have a hard time explaining like the double slit experiment or entanglement it also gives us a deeper more complete picture of reality as it probably is while you might feel uncomfortable with quantum mechanics because it is unintuitive in nature remember that nature has no obligation to be intuitive or understood by us conceited hairless apes who think we deserve to know the deepest secrets of the universe quantum mechanics is ultimately the root of reality and if you want to get a deeper understanding of this fascinating subject one of the best classes is offered at brilliant called quantum objects it consists of 15 interactive lessons on various quantum physics concepts before you know it you'll be solving problems like bohr and rutherford had to do learning science by solving problems and working on puzzles is in my opinion the best way to master a subject and at brilliant today's sponsor you can do just that it's a problem-solving website and app that allows you to go deeper and further into the world of physics and other science subjects than any video or article ever can if you want to support this channel and explore science deeper head on over to brilliant.org forward slash arvind ash to sign up for free and the first 200 visitors will even get 20 off their subscription check it out i think you'll be impressed i'd like to thank my generous supporters on patreon and youtube if you enjoy my videos consider joining them or check out some of our other videos i will see you in the next video my [Music] friend [Music] you

Channel: Arvin Ash

Views: 442,942

Rating: 4.9254236 out of 5

Keywords: quantum mechanics, atomic model, electron cloud, atomic orbital, electron configuration, energy levels, what do atoms look like, why cant we squeeze atoms, rutherford atomic model, bohr model, schrodinger equation, quantum physics explained, what does an atom really look like, what does an atom look like, de broglie wavelength, de broglie hypothesis, heisenberg uncertainty principle, why dont electrons crash into the nucleus, why dont electrons fall into the nucleus

Id: fP2TAw7NnVU

Length: 14min 25sec (865 seconds)

Published: Fri Jul 31 2020