In the gaseous state, the molecules are spread very widely apart from one another and are free to move about. If placed in a container, the molecules will occupy the volume of the container and take its shape as well.
The molecules in the liquid state are closer than in the gaseous state and less free to move about. They are in layers that slide over one another, allowing the substance to flow. If placed in a container, the liquid water will take its shape but not the volume.
The molecules in the solid state are fixed in position, only able to vibrate about their fixed points. The structure formed is rigid, it does not flow and its shape and volume are fixed.
