What does collision between electrons and atoms mean?

Question

Now, it's generally taught (and even visualised) that atoms are like balls which bump when collided with other atoms. And it's also said that electrons collide with atoms. I am reading the Drude model of electrical conductivity, there one of assumptions was made that electrons collide with ions. I actually have a problem with that, which is that when I say an atom it doesn't have any layer covering nucleus and electrons. It simply means nucleus together with electrons right? Now the same applies to ion as well. So my doubt is if we don't have any layer covering atoms why electrons are said to bounce off with atoms or molecules or ions? In simpler terms my doubt is what does electrons bouncing of ions really mean? Does it mean like atoms are balls through which electrons are bounced off?

Answer 1

One has to keep clear that there are two kinematic mathematical frames to model particles: a) the classical mechanics frame and b) the quantum mechanical frame.

Now, it's generally taught (and even visualised) that atoms are like balls which bump when collided with other atoms.

This is the classical mechanics frame.

And it's also said that electrons collide with atoms. I am reading the Drude model of electrical conductivity, there one of assumptions was made that electrons collide with ions

The collision of an electron, par excellence a quantum mechanical elementary particle, with an atom or an ion, may be modeled classically as a charged particle hitting a neutral particle or another charged particle using classical electromagnetism or quantum mechanically where one does not talk of collisions but of interactions.

an atom it doesn't have any layer covering nucleus and electrons.It simply means nucleus together with electrons right?

Wrong at the quantum level. See this simple depiction of the hydrogen atom in the Bohr model, a first approximation to the quantum mechanical solution.

This Bohr model picture of the orbits has some usefulness for visualization so long as it is realized that the "orbits" and the "orbit radius" just represent the most probable values of a considerable range of values

The nucleus itself, in size,is a dot at the center . The analogous drawing can be made for atoms in general, the electrons are in orbitals a very large distance away from the positive nucleus.

You:

In simpler terms my doubt is what does electrons bouncing of ions really mean?

It means an electron interacts with the quantum entity "ion" with a certain probability of scattering, as quantum mechanics only predicts probabilities, not tracks.

The Drude model is a classical mechanics model,

Drude model electrons (shown here in blue) constantly bounce between heavier, stationary crystal ions (shown in red).

It assumes as dimension of the atom the one imposed by the quantum mechanical binding of electrons to atoms, so if the atom is neutral it will be like a tiny ball hitting a large ball, if it is an ion like a tiny charged particle hitting a much larger charged particle. (The size and shape of atoms and molecules is determined by the quantum mechanical solutions for the atoms and molecules)