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electrostatic force

Note by Vyom Chaturvedi
4 years, 2 months ago

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Why does the electrons revolve around the nucleus ,even though both are oppositely charged? Vyom Chaturvedi · 4 years, 2 months ago

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@Vyom Chaturvedi Without going into Quantum Mechanics, the simple answer to your problem would be that the electrostatic force acts as a centripetal force causing it to assume circular motion (not entirely true) about the nucleus. Think about the Sun and the Solar System, circular (or more technically elliptical) motion prevents the planets from falling into the Sun. You may ask why an accelerating charge does not radiate electromagnetic energy (as it ought to) and thus fall into the nucleus in this case. Again the simple answer is that at certain energy levels or orbits, the electron does not radiate electromagnetic energy. Maher El Ghor · 4 years, 2 months ago

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@Maher El Ghor But you need to remember that electrons don't act like particles, the behave like waves essentially, and thus the whole planetary analogy is flawed. Grant S. · 4 years, 2 months ago

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@Grant S. No, they behave as both particles and waves do- though essentially they are particles thus they do have orbits just like planets do. The differences between planetary orbits and electron orbits are subtle, and lie in the depths of Quantum Mechanics as I already mentioned. Bear in mind that the person who posed this question is 13 years old so it does not help in the slightest to speak of solving Schrodinger's equations to find the probability density of an electron being at a point in space which, when plotted as a curve, gives us spherical or dumb-bell shapes etc. Maher El Ghor · 4 years, 2 months ago

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think so as the electron and protons in nucleus are less tha a distance of 0.8 fermi meter which is the range of nuclear force. nuclear forces are charge independent and are attractive in nature Sawan Singh · 4 years, 2 months ago

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The electron doesn't revolve around the nucleus - that's just a very simplistic model. You must bear in mind that electrons are more like waves when around an atom, and you can think of them as forming a circular standing wave around the atom, if you want an analogy you can think of guitar strings, but maybe make the string loop back on itself. I think the number of nodes in the wave is significant, and can determine the electrons shell/orbital/energy level. Another way to think about it, is by looking at the chemistry orbitals; s, p, d, f. By the uncertainty principle, we cannot know for certain where the electron is, so we can create a probability distribution to map where the electron might be. These distributions do actually go through the nucleus, and the distribution is centered around the nucleus, because, as you say, there are opposite charges, this is what keeps the electrons in the atom. However, they wont 'collapse' into the nucleus because of quantum mechanics - the uncertainty principle basically shows that you cant confine its position like that, and in addition, the weak force will make it such that it wont actually interact with the nucleus in such a way to be damaging, although on occasion it is possible for interaction to occur. You might want to think of the weak force acting as a counterbalance for the electromagnetic force which is attracting the oppositely charged 'particles'. Basically, its hard to explain - but theres a lot of complicated mechanisms at work. Ben Blayney · 4 years, 2 months ago

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@Ben Blayney Hello Ben,

First off, technically speaking, electrons do revolve about the nucleus- but not in a circular path.

Secondly, I noticed that you mentioned that the distributions go through the nucleus which is not true except for s orbitals. Since l = 0, the electrons have no angular momentum. From a classical perspective, this means that electrons are effectively traveling back and forth through the nucleus, not around it. Now notice that if you compare an atom of H to an atom of Mg, the electrons in the 1s shell would have to be vastly more energetic in Mg than in H to travel through the nucleus- which is a paradox. Therefore we must consider it using the rules of Quantum Mechanics since it is both charged and has a very small mass. Thus we can use your analogy of a standing wave, though it would simplify matters if we considered the electron as a string consisting of two simultaneous versions of itself where one travels, say, clockwise and the other anticlockwise (in reality, infinitely many components exist since there are an infinite number of planes) These components can be thought of as being refracted by the powerful electric field of the nucleus so they end up curving about it without ever striking it. Bear in mind that there is a difference between this refraction effect and attraction. Indeed it is this effect that prevents the probability density from reaching infinity at the nucleus ie. from striking it. In other words, for an electron which behaves a standing wave- two waves travelling in opposite directions, anti-clock and clock- the combined waves curve around the nucleus rather than striking it. As I said, this is essentially a quantum event which holds if objects are light enough so that particle behavior is no longer viable for them. Instead, you get waves that, with perfect spherical symmetry, curve around the nucleus, never obtaining enough energy (which increases its particle behavior) to collide with that nucleus.

Finally, you incorrectly used the Uncertainty Principle in your final argument (incidentally your use of it contradicts what you said earlier about the electron being able to travel into it) Alone, the uncertainty principle allows for an electron to be moving anywhere in space with any momentum- you just can't measure both at the same time! However you correctly stated that they don't collapse into the nucleus because of Quantum Mechanics, though the reason being that the electron can only occupy certain energy levels, at the very least the ground state, which prevents it from reaching the nucleus (though you would have had to factor in the second point about the electrons curving around the nucleus for the s orbitals)

Hope you found this interesting, I certainly do, and it would be splendid if you would like to discuss these things further! Let me know :) Maher El Ghor · 4 years, 2 months ago

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also when one electron gets closer to the nucleus , there is the possibility of another electron repelling it ( as both are moving towards the nucleus). Aravind Kukkila · 4 years, 2 months ago

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http://in.answers.yahoo.com/question/index?qid=20100622044513AAJEP6f Aravind Kukkila · 4 years, 2 months ago

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Strong Nuclear Force... Michael Sheng · 4 years, 2 months ago

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@Michael Sheng I think you mean to say 'weak' nuclear force Abhro Rahman · 4 years, 2 months ago

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