The term state when used in reference to matter is an arbitrary term. The state of mater is a classification used to separate different materials into broad categories. Chemists find it very convenient to identify a material by its state, but in reality matter tends to fall on a continuum rather than falling into discrete categories. Furthermore, by changing temperature or pressure, most matter will change from one state to another.
Classical chemists once divided all matter into solids, liquids and gases. A solid was defined as a material that maintained a constant shape until acted upon by an outside force like a hammer. A liquid was defined as a material that would flow and if poured into a container would assume the shape of the lower portion of that container. A gas was defined as a material that not only flowed but expanded to completely fill what ever container it occupied.
These there states of matter could be explained by saying that the molecules of a solid remained in one location like a soldier in a regiment. the kinetic energy of each molecule would be reflected in a vibration of the molecule. A liquid would be explained by saying that the molecules were free to move about but were kept by gravity from moving above the surface of the liquid. Said molecules bounce off the walls of the container and off of each other. In a gas, the molecules are completely free to move in any direction until they bounce off of any wall of a container or into another molecule.
Eventually high energy chemists began placing an electric charge on the molecules of a gas. Was it still a gas? In some ways it acted like a gas, but some properties were unique. This new material did not always assume the shape of its container. Magnetic fields could be used to shape the mass of this charged gas into spaces smaller than the container. The charged gases were called a plasma. Some chemists call plasma the fourth state of mater because it no longer acts like a gas.
So what do you call a solid that flows at room temperature? Yes, many materials that people consider to be solids flow. The solid may change shape over a period of hours or over a period of years. Most plastics will slump or flow, slowly changing shape as though it were a liquid moving in slow motion. Over a mater of years, careful measurements will show a small amount of flow in metals like copper or steel.
What would you call a polymer solution that can be pulled over the side of a beaker as though it were a rope? liquids are not suppose to do that, but this solution is certainly not a solid.
When one looks with an open mind, one finds few things that are true solids, liquids or gases. Nevertheless, it is practical for humans to describe matter as being solid, liquid or gas. If one works with charged gases, it is practical to add plasma as a state of mater. The use of these states of matter helps us to communicate with each other. As chemists use these four terms, they keep in mind that matter does not always follow all of the rules that humans impose on them.
