Question

Why negatively charged electrons don’t fall into thenucleus?

Answer 1

Answer:

Electrons are not little balls that can fall into the nucleus under electrostatic attraction. Rather, electrons are quantized wavefunctions that spread out in space and can sometimes act like particles in limited ways. An electron in an atom spreads out according to its energy.

Answer 2

This is an excellent question - it is exactly what Ernest Rutherford wondered in when his team discovered that atoms had tiny positive nuclei (read how they discovered that here: ). Yes - their first thought was that the motion of the electrons prevented them flying into the nucleus. They imagined the electrons would orbit the nucleus like little planets around a star, but they soon realised this couldn’t be the whole story.

The problem is that, according to electrodynamics, if you change the direction of a charged particle this generates an electromagnetic wave, which would take energy away from the particle. An electron moving in a circle should be continually radiating electromagnetic waves, which means it would lose speed and get closer to the nucleus until, eventually it would crash into it. Doing the calculations revealed that atoms should collapse in a fraction of a second.

So what’s going on? Neils Bohr suggested an alternative planetary model in which electrons stay in fixed orbits around the nucleus. While they are in one of these orbits they do not radiate electromagnetic waves. They can jump from a low orbit to a high orbit if they absorb just enough energy - the difference in energy between the two orbits. They can jump from a high orbit to a low orbit by emitting a precise amount of electromagnetic energy - the difference between the two orbits.

Note that Bohr did not have a good explanation for why electrons behave like this, but it was easy to show that it was a good approximation for what was going on. Physicists had known for a long time that atoms absorb and emit electromagnetic radiation at fixed wavelengths. Each element has its own characteristic ‘spectrum’ - colours of light specific to that kind of atom - but no one knew why (light is a form of electromagnetic radiation). Bohr’s model of the atom hinted at an explanation for spectra.

It took many years to get a more complete theory of electrons in atoms. The theory is called quantum mechanics, and is both the most successful and most confounding theory physics has ever come up with. With quantum mechanics you can calculate where you would expect to find electrons in atoms. It turns out that it is not neat circular orbits but more complex 3 dimensional shapes, which were given the name ‘orbitals’ because they are conceptually similar to orbits. Electrons can jump from one orbital to another by absorbing or emitting a precise amount of energy - the difference in energy between the two orbitals.

TL;DR: Electrons in atoms exist only in specific ‘orbitals’ - 3D shapes around the nucleus. They can get from one orbital to another, but not anywhere else.