English Resumeđź“š CLASSIFICATION OF MATTER 1.Defenition of matter Matter is everything around you. Atoms and molecules are all composed of matter. Matter can be classified into two categories: pure substances and mixtures.A sample of matter can be a gas, a liquid, or a solid. "Phase of matter" ATOMS atom is the smallest constituent unit of ordinary matter that has the properties of a chemical element. Atoms are very small; typical sizes are around 100 picometers (a ten-billionth of a meter, in the short scale). MOLECULES The molecule is a group of atoms (at least two) that are bonded together very ...