Sound Waves, are mechanical energy, and thus they require a mechanical medium to travel. sounds are created by the vibration of particles when hit by the sound wave. This means that the medium which allows sound to travel must hold certain properties that can conduct sound. In Air, liquid and solid, the particles are close enough that when a sound wave hits the particle, the particle can vibrate and hit the next particle to cause more vibration, thus creating sound.
Sounds cannot travel in a vacuum because they have no medium in which they can travel through. Vacuum is empty of matter, so there is nothing for a sound wave to propagate through. since Sound relies on the movement of particles to propagate and vacuum does not contain any particles, there can possibly not be any vibration between particles. Hence sound cannot travel in vacuum.