Anything that occupies space and has mass is known as Matter. So everything that we see around us is known as Matter. The matter is made up of Atoms and Molecules. Depending upon its physical state, the nature of matter falls into three categories: Solids, Liquids and Gases. All matter is made up of atoms, which are in turn made up of protons, neutrons and electrons. Atoms come together to form molecules, which are the building blocks for all types of matter, according to Washington State University. A physical change involves the conversion of a substance from one state of matter to another, without changing its chemical composition. There are gaps between the molecules of matter called intermolecular space. The change of state of a matter from one form into another is called inter-conversion of states of matter.