why electrons aren't at the nucleus?

Question

why they go around in orbits?

Answer 1

They are lighter in weight than the neutrons and protons. Look at the Earth. The heavier substances are clumped together, the Earth itself, while the atmosphere is not as heavy, and goes around the heavier Earth.
The same is with the the heavier neutrons and protons. They have more mass, and therefore more gravity, so they are pulled closer together. While the electron, is lighter, and energetic. So the electro goes around in orbits of the nucleus. It's like a miniature planet and moon system. The weak nuclear and strong neuclear forces have more affect at the atomic level than gravity, but I can't explain those things.
Though the gravity helps, it's mainly the attraction of opposite charges that pull the electron to the neucleus, or more specificaly, the proton(s). The energy of the electron, however, is so high that it's rate of movement never allows it to stop and actualy become a part of the neucleus.

Answer 2

They don't.

They exist in a sort of cloud around the nucleus. The shape of this cloud is given by solutions to the Schroedinger equation, and is complex. These clouds are often called orbitals because of the previous - and obsolete - model of the atom of orbiting electrons (electrons could not orbit the nucleus because they would radiate away all their energy if they did).

Orbital shapes can be very complex - especially for alrger atoms - but for some orbitals the probility of an electron being near the nucleus is not zero.

Answer 3

Argh...those answerers who are trying to answer your question by equating moons to electrons, planets to nucleii, and gravity to EM forces are waaay off the mark. The orbit, Bohr model has long been replaced by the quantum mechanics model. Look this over:

"The Bohr model is a primitive model of the hydrogen atom. As a theory, it can be derived as a first-order approximation of the hydrogen atom using the broader and much more accurate quantum mechanics, and thus may be considered to be an obsolete scientific theory. However, because of its simplicity, and its correct results for selected systems (see below for application), the Bohr model is still commonly taught to introduce students to quantum mechanics." [See source.]

Electrons are not little pieces of something orbiting around the nucleus like the Moon around Earth. They are best described as packets of waves that cancel each other out beyond some finite distance, which determines the dimension of electrons in the classical sense. At best, these wave packets jitter around and they do that according to well defined probability distributions, which is the strength of quantum mechanics.

The thing you are calling an orbit is just the shell of a sphere shape where the probability density function predicts we will most likely find the electron around the nucleus. And this probability density function is three dimensional in space; so it envelops the atom like a shell with its thickest part at the most likely (expected) distance from the nucleus. And, as your one answerer correctly pointed out, on the big atoms, some electron probability distributions just about touch the nucleus.

Electron packets carry intrinsic energy in their waves. (Waves are always energetic.) The amount of energy they carry determines where the expected cloud shell of an electron will be outside the nucleus. The electrons will be "outside" the nucleus because they siimply do not have enough intrinsic energy to be inside. Their probability density distirbutions simply do not include the nucleus of an atom.

What is interesting is that these expected distances (R) from the nucleus are discrete. This means that the most dense part of the probability distribution cannot be some distance in between certain multiples of integers from the nucleus. For example, for a given nucleus, an electron might be R, 2R, 3R and such where NR is a specific distance from the core and N = integer. There can be no 1.3R for example, because 1.3 is not an integer.

Which NR an electron shell is most likely to be found depends on the energy of the wave packet. More energy means a smaller NR; less energy means a larger NR.

If we excite an electron so it receives an energy boost, it will jump to a smaller NR. But that is unnatural for that electron; so it jumps back to its original, natural shell. When it does that, it emits the energy it absorbed as a photon, which can be seen via spectograph. That light emissions, the photon, is called the Zeeman Effect.

So we in fact, can give electrons more energy; so it could be that we could give them enough to actually fall within the nucleus. There are lot of other issues in doing this we won't go iinto. But it does seem feasible on the face of it. In fact, there have been experiments wherein electrons were forced to mix with nucleii. Check this out:

"Usually the electrons of an atom have little regard for the internal affairs of the nucleus. The nucleus typically makes transitions from one state to another with energies of millions of eV, whereas most electronic transitions occur at mere tens of eV or less. Recently, two experiments have bridged this gap between electrons and nucleus in dramatic ways. Reporting in the 28 August PRL, physicists in Japan have excited a nucleus via the atomic electrons, while a European collaboration publishing in the August Physical Review C has obtained direct evidence of the reverse process. In both cases, the energies of the nuclear transitions and electronic transitions must be closely matched." [See source.]

Answer 4

In fact, in 1897, J.J Thomson put forward an atomic model in which all electrons were embedded in a positive sphere as plums in the pudding.

That model could not explain the emission of light rays by an atom.

Only if the electrons were situated out side the positively charged nucleus in certain discrete energy levels, the atom can emit light rays when perturbed.

Therefore electrons cannot be inside the nucleus.

Many observed physical phenomenon cannot be explained if electrons were considered to be inside the nucleus.

Answer 5

the simple answer is the same as why is the earth not in the sun. It is because the electrons are far far less massive than the protons and neutrons in the neucleus.
Just like the earth is smaller than the sun so the earth rotates around the sun instead of the sun around the earth. But the same principle holds as it does with orbital mechanics as it does with quantum mechanics. Electrons have a certin ammount of energy, and that forces them to be in "orbit" around the more massive neucleus.

Why do they not fall in to the center, welll that is a much more complicated question that involves quantum mechanics. Basicly it is that the electrons are not particles and exist in an orbit around the center, and do not move. They exist throughout the orbit, thus if they do not move they can not loose energy and can not fall in to the center.

Answer 6

Because the nucleus is already full of protons and neutrons. This doesn't leave much for the electrons to do except fall into orbits around the nucleus.

It's a rough life in the world of quantum physics, but them's is the rules.


Doug

Answer 7

In a simple scenario, the electrons have a long wavelength compared the size of the nucleus and so can not be confined but they can orbit such that thier path is an integer multiple of the wavelength (a standing wave) and still be confined. This is called the periodic boundary condition.

Answer 8

Epidavros' reply is correct and concise. I might add that it's Heisenberg's uncertainty principle that prevents electrons "to be" at the nucleus because then their position would be known exactly denying the same principle.

Answer 9

Since,the protons are positively charged {neutrons too are present but neutrally charged} and electron is negatively charged they must attract each other but since electrons move with a certain velocity they are forced to revolve around.They do not fall into the nucleus due to the centripetal force.

Answer 10

i think it is dew the positive and negative fourse which attracts and repels holding them in orbit

not sure wasn't too good at chem