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for one, electrons exists as wave probabilities above the nucleus. That means it can be inside the nucleus but 95% of the time it stays outside.
This is one of the classical problems that motivated the study of quantum mechanics. Classically, an electron is modeled as a particle moving in an elliptical orbit around the nucleus, with the electric force replacing gravity as the force binding it in orbit. The problem is that the electron is accelerating, and an accelerating charge radiates energy, so the electron will eventually lose its energy and fall into the nucleus. However, there are two results of quantum theory that make this situation impossible. One result is that particles don't have well-defined trajectories as they do in classical physics, so we can't even say that the particle is 'orbiting' the nucleus; we can only describe a probability that at a particular moment in time, it is in a certain position. This probability will depend on the energy of the electron; higher-energy electrons will have a higher probability of being further from the nucleus. Another result is that the electron is only "allowed" to have certain amounts of energy; that is, instead of a smooth scale of energy, there is a sequence of "allowed" levels, with a gap between each. There is no way that an electron can gradually lose energy and fall in; it must lose a chunk of energy at a time to jump the gap. Furthermore, by solving the Schroedinger equation we can get a mathematical description of every allowed energy level of the electron, and we find that first, there is a lowest energy level, and second, an electron in this energy level is still some distance away from the nucleus. So, the lowest possible energy of the electron that is consistent with quantum mechanics is still a positive energy state, keeping it away from the nucleus.
opposite forces, if not let me know.
eh? what opposite forces?
charges, I think I got that one right.
eh? charges? isn't that suppose to be why the electrons are supposed to go into the nucleus?
bohr somarfield gave the theory, electrons travel not in circular path but in a elliptical path.
The picture we often have of electrons as small objects circling a nucleus in well defined "orbits" is actually quite wrong. The positions of these electrons at any given time are not well-defined, but we CAN figure out the volume of space where we are likely to find a given electron if we do an experiment to look. For example, the electron in a hydrogen atom likes to occupy a spherical volume surrounding the proton. If you think of the proton as a grain of salt, then the electron is about equally likely to be found anywhere inside a ten foot radius sphere surrounding this grain, kind of like a cloud. The weird thing about that cloud is that its spread in space is related to the spread of possible momenta (or velocities) of the electron. So here's the key point, which we won't pretend to explain here. The more squashed in the cloud gets, the more spread out the range of momenta has to get. That's called Heisenberg's uncertainty principle. Big momenta mean big kinetic energies. So the cloud can lower its potential energy by squishing in closer to the nucleus, but when it squishes in too far its kinetic energy goes up more than its potential energy goes down. So it settles at a happy medium, and that gives the cloud and thus the atom its size.
eh? elliptical ?
Man, this is bad. lol
It's due to the centripetal acceleration. This is the same way planets don't crash into the sun despite its immense gravitational pull.
see up for akash's explanation though.
Pauli exlusion principle...??
I actually got no time to answer, but wanted to point out that pretty much all answers here are total bullcrap - please don't listen, isaac.maria.9. Akash1477 answer is _by_far_ the best one, although I do not know, why they are all talking about an elliptical orbit. Never seen a physicist not use a circle when deriving the orbits with de Broglie's wavelength... Just read this: -> http://en.wikipedia.org/wiki/Bohr_model
just becoz of equal and opposite force called centripital and centrifugal force....
Schrodinger introduced his wave equation on a whim to see if it would work. If particles could act like waves why not use a wave equation to describe them. It worked i.e. explained observed experimental results. It also showed that even though an electron was attracted to a nucleus there where only a discrete number of energies (negative because the electron is bound by the nucleus) allowed and the most negative was not as negative as classical theory might predict. Thus the electron is not pulled into the nucleus. Interestingly the solution to his equation does allow a bit of the electron to occupy the same space as the nucleus. it also showed that if the electron was farther from the nucleus the energies states allowed became more numerous and closer together to the point that the electron could have almost any energy that is classically allowed if it was far enough away.