Why don't particles/molecules travel in propagation of sound energy? I just began learning about the topic of sound energy in physics and I already have lots of question that is not being explained with a simple google search. In my research so far, I have learned that in the mechanics of the propagation of sound, it is not the molecules/particles that travel but the energy that is transferred from molecule to molecule. So now with this fact in mind, my question is then that in propagation of sound, why do molecules/particles not travel and keep on traveling in one direction, until its reaches somewhere like the ears of some living being or something. Why does it vibrates, back and forth in stead? Like, what is causing the molecules to move back after it has moved forward where it is carrying the energy of sound?
The reason why I am asking this is that so far from my understanding of sound energy, I tend to  conceptualize sound energy as something that originated with some kind of mechanical or contact based force. So like, when I tap/touch on a molecule , that molecule travels a certain distance, which in turn taps/touches another molecule in its path that in turn travels a certain distance, so on and so forth. This situation, in my understanding, is similar to me pushing a macroscopic object like a table by hand, and in this case we know from everyday experience when you push a  table, the table as a whole together moves a certain distance. It doesn't travel back and forth. So, thus, unless there is a flaw in my understanding of sound energy so far, my question then becomes that why do molecules/particles in sound energy vibrate in stead of traveling a certain distance? If anyone can add to this question, it will be greatly appreciated. Thank you.
 A: 
So like, when I tap/touch on a molecule , that molecule travels a
certain distance, which in turn taps/touches another molecule in its
path that in turn travels a certain distance, so on and so forth

It is right. It is the same principle of a row of coins. When the first is hit by a moving coin, the last of the row moves. The intermediate coins also moved, but it was an very small longitudinal vibration. The energy of the first coin propagated to the last one by these mechanic vibrations.
In the sound waves in the air, the short longitudinal path of each molecule corresponds to the coin vibration.
A: The situation get messier than that but you are on the right track.  Whatever acts as the source of sound in a fluid pushes on fluid particles and what is propagating is an increase in local density (and/or pressure) of the fluid.  If the particles are pack up against each other then rather than the particles you pushes moving to someone's ear they push neighboring particles etc.  At the location of the source at the instant that it is turned on it either makes a pocket of "more" dense air in front of it or "less" dense, depending on whether it pushes forward or pulls back.  This is all it takes to create a single pulse.  This density change is what travels and that may or may not correspond to particle movement.  The reason I say it's messier than that is because molecules in air or water and not bound to a specific location as they are in a solid.  So once they start moving they can in fact keep moving in the direction of the sound.  This is how fluids work, they are random and chaotic.  The picturesque descriptions in some science books do not do justice to what is happening at the particle level.  We try to develop a description of sound as small disturbances in the density, pressure, and other thermodynamic state variables of the fluid.  But in fact making sound can also make "wind", or steady flow.  Our assumptions that these two things can be separated and each described by a distinct separate set of equations is often violated in real life.  Acoustics is really a small piece of fluid dynamics and that makes it very exciting to study.
