1) How does the Earth revolve around the sun?
Here, you have to remember that the Earth is moving at great speeds. It is this movement that keeps the Earth from falling into the sun. Now recall Newton's first law of motion: inertia, a body in motion tends to stay in motion. Because of inertia, the Earth would like to move in a straight line. However, due to the gravitational force between the Earth and the sun, the Earth is constantly "falling" toward the sun. This gravitational force curves the Earth's preferred straight line of motion into a circle. You can think of this as the sideways motion of the Earth keeping it from ever reaching the sun (see http://en.wikipedia.org/wiki/Orbit#Understanding_orbits for a better explanation).
Early models of the atom were based on this "planetary orbit" model. Electrons travel very fast and their fast speeds allow them to orbit the nucleus like planets orbit the sun.
2) Why is this model is incorrect?
Now, if you have studied electricity and magnetism, you should see a problem with this planetary model. The electron is traveling in a circle which means that it is constantly accelerating (note: although it is not changing speed, it is changing velocity because velocity accounts for the direction of the electron as well as its speed), and the electron has a charge. From the laws of electricity and magnetism, we know that accelerating charged particles should radiate energy (in the form of electromagnetic radiation). Because energy is conserved, this radiated energy would decrease the speed of the electron (lowering its kinetic energy), causing it to slowly spiral into the nucleus. So, we're back where we started, classical physics predicts that an electron will fall into the nucleus!
3) WTF?! What's really going on?
The real explanation for why an electron does not fall into the nucleus comes from a fundamental concept in quantum mechanics: the Heisenberg uncertainty principle. Put simply, it states that you cannot know the position and momentum of a particle simultaneously. More rigorously stated, the product of the uncertainty of the position of a particle (Δx) and the uncertainty of its momentum (Δp) must be greater than a specified value:
$$\Delta x \Delta p \geq \frac{\hbar}{2}$$
Now, as the electron approaches the nucleus, it's uncertainty in position decreases (if the electron is 10nm away from the nucleus, it could be anywhere within a spherical shell of radius 10nm, but if the electron is only 0.1nm away from the nucleus, that area is greatly reduced). According to the Heisenberg uncertainty principle, if you decrease the uncertainty of the electrons position, the uncertainty in its momentum must increase. This increased momentum uncertainty means that the electron will be moving away from the nucleus faster, on average.
Put another way, if we do know that at one instant, that the electron is right on top of the nucleus, we lose all information about where the electron will be at the next instant. It could stay at the nucleus, it could be slightly to the left or to the right, or it could very likely be very far away from the nucleus. Therefore, because of the the uncertainty principle it is impossible for the electron to fall into the nucleus and stay in the nucleus.
Allen_Wolf said:Why doesn't electrons fall into the nucleus of an atom?
BvU said:I think Allen is asking a sensible question and deserves an understandable answer. Earth has angular momentum that keeps it orbiting around the sun. Electrons in the lowest energy levels don't have that and still don't annihilate the nucleus.
Electrons are negatively charged particles that orbit the nucleus of an atom. In atomic collapse, they play a crucial role in maintaining the stability of the atom by balancing the positive charge of the protons in the nucleus.
Atomic collapse occurs when an atom loses its balance due to external factors such as high energy collisions or intense radiation. This causes the electrons to become unstable and collapse into lower energy levels, resulting in the atom's disintegration.
In some cases, atomic collapse can be reversed by supplying energy to the atom, causing the electrons to move back to their original energy levels. However, this process is not always possible and depends on the extent of the collapse and the type of atom.
Atomic collapse can significantly alter the properties of an atom, such as its size, shape, and reactivity. This is because the number and arrangement of electrons determine an atom's chemical and physical properties, and a change in these factors can result in a completely different element.
While atomic collapse can occur naturally in certain conditions, it is primarily observed in controlled environments such as in nuclear reactors or particle accelerators. Natural atomic collapse is also responsible for phenomena such as radioactive decay and stellar explosions.