Pris Posted November 16, 2003 Report Share Posted November 16, 2003 I have been walking around with this question for quite some time now, asking some of my fellow students (I study Chemistry), and some teachers, but noone seems to know.. so here I go again: Why doesn't electrons hit Protons? - they attract eachother and if you look at a SP^3 hybritized carbon atoms the one half of the 8-motion in the orbitals is quite close to the core... But even the normal P-orbitals it seems to be close.. I know orbitals is all aproximations, and flawed ones at that, but there's other arguements to why it should happen.. say when you excite electrons (making them emit light on their way back) you make two negatively charged particles hit eachother.. how strange is that? Ok, I could keep rambling about that.. I've obviously got something wrong, or quantum mechanics is even worse at describing than i thought. :-/ Have a nice day gents and ladies. - Pris Link to comment Share on other sites More sharing options...
Tormod Posted November 17, 2003 Report Share Posted November 17, 2003 Hi Pris, welcome to our forums! Forgive my ignorance, but I thought electrons did not collide with each other. In a particle collider they use electrons and positrons (positively charged electrons). Electrons repel each other, for the exact same reason protons and electrons attract. This is simply due to electromagnetism. Protons can collide with each other, however. This is for example what happens with fusion reaction in the Sun. A free proton hits a hydrogen atom, creating an atom with two protons and an electron. this is a no-no, so one of the protons turn into a neutron. this "temporary" element is deuterium - and two deuterium atoms can bind to form a helium atom. (But I guess you know this already) As for why electrons do not collide with protons, well, I don't have any explanation other than the whole reason why quantum physics is prefixed with "quantum" is that electrons can only have certain levels of energy (ie, "quanta"). Thus, their position related to the proton is fixed. they can move towards or away from the nucleus in certain steps (which emits photons), but they never fall into it. I think that if an electron could collide with a proton, the nucleus in any atom would be highly unstable (I may be very wrong here). Not a good answer, perhaps, but at least an attempt! Tormod Link to comment Share on other sites More sharing options...
Pris Posted November 17, 2003 Author Report Share Posted November 17, 2003 Thank you mista I wouldn't say I know all that with fusion and stuff.. I study chem you see, although physics in some ways is alot more interresting. (chemistry just seems to have more practical use to me)... oh, and I'm on first semester, so there's a billion things I don't know. But still... your answer only really tells me how lousy quantum mechanics is at explaining what's going on in reality... or maybe the answer lies in what energy is.. my understanding of it is unfortunately pretty vague.. I mean.. to me it makes no sense at all that two particles, that attract eachother, can't hit eachother because one of them is full of energy. Is there any physical reason as to why it can't lose its last bit and then just ram into the core? - strange. - Pris Link to comment Share on other sites More sharing options...
Roberto Posted November 17, 2003 Report Share Posted November 17, 2003 The question of why electrons do not hit protons in the atom exists since the early days of the old Rutherford model (electrons orbiting protons like planets orbite the sun). The argument is that, according to the CLASSICAL laws of electromagnetism, charged particles when accelerating emit radiation and then, if the electron is moving around the proton, initially on a stable orbit, it will lose energy and hit the proton. Of course that according these classical laws, you cannot have an electron st rest in the atom, because it would be attracted and hit the proton too. But, as we can see everyday, and as you said, it does not happens. You're mistake is to try to understand the quantum model of the atom in a classical way. You cannot apply classical electromagnetism to the atom, because you will always end up with the electron hitting the proton. The quantum model of the atom do not attribute a definite place and velocity to the electron, only probabilities according to quantum laws. Now, if you calculate the probability of one of the electrons being in the same place as the proton in the nucleus you will get the answer zero, so that's why they don't hit. Maybe this WHY will not make you happy, but we don't know why quantum mechanics is this way. We discovered it by means of experiments. We just know that nature is this way. We still don't know why. (At the moment ) ) Link to comment Share on other sites More sharing options...
Pris Posted November 23, 2003 Author Report Share Posted November 23, 2003 Hey.. thanks.. I see the obvious flaw trying to put 'the real world' so to speak into the laws of quantum mechanics. And as you say, that *is* quite a mistake. You must understand that this is all very hard to put words to for me, as I'm forreign and it's quite new to me, so I don't know alot of common terms used.. I usually have to read everything 3-5 times before I think I understand it.. So anyway.. The (for me) best answer I got was from someone on IRC. She (yea, she) pretty much just said I shouldn't imagine electrons as particles. That is, some small ball with a charge. But rather as a wave. This wave would increase it's energty as it moved away from the atom (I asume it's wave length would become shorter, but I dunno), and when it approached the core it would lose energy, and at the core it wouldn't be a wave anymore since it had lost all it's energy. That *kind* of makes sense to me... Maybe it's the same thing you're saying Roberto, and if so, then I'm sorry hehe.. But alas, I'm a physics-rookie and all this is very abstract and diffuse to me. :-) Greetings - Pris Link to comment Share on other sites More sharing options...
Tormod Posted November 23, 2003 Report Share Posted November 23, 2003 Pris, you wrote: "your answer only really tells me how lousy quantum mechanics is at explaining what's going on in reality" Quantum mechanics is not lousy at explaining anything. It is rather the other way around - it is difficult to explain quantum mechanics. Countless books have been written about QM and I dare say I have read more of then than most in this forum (/*duck*/). But I still haven't got a clue what it's all about. EXCEPT the fact which Roberto mentions, that there is indeed a difference between the "real world" and the "quantum world". Why is this? Well, in quantum physics scientists observe and predict things which simply cannot happen on a large scale. For example, the strong/weak force interactions do not work on distances larger than the atom. An electron does not "feel" gravity in the same sense we do it. The "real world" is very well described in what is called classical physics and explains why apples fall down and why a prism breaks white light into different colores. QM deals with the very fundamental issues in the Universe, like why particles can behave both as particles and waves. This particle/wave duality/which we have discussed before in this forums) was what clinched it for Einstein in the first place. The history of Quantum mechanics is very interesting, and it is important (in my eyes) to know what went on in the past century, because a lot of things happened and it taught us a new way to look upon things. Here is a good start: http://www-gap.dcs.st-and.ac.uk/~history/HistTopics/The_Quantum_age_begins.html Tormod Link to comment Share on other sites More sharing options...
Roberto Posted November 23, 2003 Report Share Posted November 23, 2003 Hi, Pris. Don´t worry if you feel difficult to make a picture of QM in your mind: everyone has this difficulty, even physicists. But I should correct a little what you said in your last answer. It is not totally correct to say that you can´t put the real world ionto the laws of QM, because the QM is what happens into the real world. When I say "Classical Physics" I mean the kind of physics that were used before we discovered QM. The laws of physics before QM described very well "big things", I mean, things and phenomena we can see everyday without the help of microscopes and other sophisticated devices. These laws work very well with those things and you will never see an engineer use QM equations to project an airplane. Classical laws are approximations of quantum laws, but both refers to real world, only the scale is different. Keep in mind too that htey are not different laws, but classical laws are just what happens with quantum laws when you neglect effects that we will not see everyday. If you ask to any physicist, he will say that in the end, the real world is quantum. Another thing. This interpretation you described that you can think of the electron as a wave that lose energy as it goes to the nucleus is an interesting mental picture, but is not strictly correct. The electron is not a wave, as far as we know. One curious thing that is never said for the general public is that QM equations are formulated for point particles, i.e., if you look at the equation, the electron is indeed considered as a particle, but with strange properties that resemble waves sometimes. I will insist to you that the QM correct picture is that of the orbitals. The orbitals will give you the most probable points to find an electron with some specific energy. Inside the orbitals, the electron is somewhere doing some movement that we simply cannot tell what is. I think that that is the most ambiased view. If you try to fit the electron in the wave or particle category you learned in school, it can help you to understand some phenomena, but will not be correct and may lead to some misconceptions. When Bohr state the complementarity principle, saying that in an experiment the electron shows its wave qualities or its particle qualities but not both at the same time, the point is that the properties of electrons are so strange to the classical physics that we cannot fit it in one of these two categories. Don´t worry if it sounds strange and if you feel a disconfort with QM. Maybe you will never be happy with it, but it has in its favor the experimental evidence. There isn´t a single known experiment in physics that violate the predictions of QM. That´s why physicists had to accept it even being so strange. Link to comment Share on other sites More sharing options...
wholloway Posted November 26, 2003 Report Share Posted November 26, 2003 I have also heard electrons described as waves. It was used to explain why electrons are found in thier different orbits or shells, and not in-between. The smallest quanta of energy of an electron locates the electron in its lowest shell. Remove the last quanta and the electron goes with it. I would conject that the only reason electrons are considered particles is because of the trails in a vapor chamber or the point of light emitted by a photo plate. Link to comment Share on other sites More sharing options...
Roberto Posted November 26, 2003 Report Share Posted November 26, 2003 You're ritght, wholloway, when you said that electrons are considered as particles because they let trails in vapor chambers. That's how J.J. Thompson proved them to be particles. They have charge and mass and are deflected by electromagnetic fields and gravity. Particularly, you can see the effect of them being deflected by electromagnetic fields in the auroras. You can say that it is not enough to call them particles, but if is not enough, what would be? I can give you my word that in QM electrons are treated as point particles. The waves you heard about are not the electron itself, but the wave function, a function that has information about the electron. Indeed, the wave function has all the information we can have about the electron in QM. The explanation that electrons fit in their orbits because they're waves is an old one, suggested before the modern QM was discovered. Electrons do not orbite the atom, as I already said, we don't know what sort of movement they do inside the orbitals. Electrons got stuck in orbitals and they do not exist outside them because that's the solution for the Schroedinger Equation: the orbitals give the probability density of an electron with some quantum numbers being in some place in space. Even the wave characteristics of the electron can be calculated and explained by the Schroedinger Equation (well, at least if we talk non-relativistically). I do not know any link devoted to science divulgation that explain it in this way, but remember when people talk about string theory? String theory is a theory where instead of particles (0-dimensional objects), you consider that electrons, quarks and so on are little strings (1-dimensional objects). That's because in traditional QM they're considered as particles. It's very important to keep one thing in mind: do not confuse the electron with the wave function of the electron. They're formally different things. Link to comment Share on other sites More sharing options...
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