The point in the middle of a destructive interference is called a node and it never moves. The angle between the incident wave and the normal is the same as the angle between the normal and the reflected wave. This change is called refraction. When a wave travels through a small hole in a barrier, it bends around the edges. This is called Diffraction.
Sound waves are longitudinal waves produced by variations in air pressure.
A vibrating source pushes molecules in air back and forth, creating areas of compression and rarefaction. When a molecule moves, it collides with the next one and makes it move too. The energy of a sound wave travels away from the source trough a series of molecule collisions parallel to the direction of the wave. Sound cannot travel through a vacuum. Actually, sound waves move faster through liquids and solids than through gases.