In this lesson our instructor talks about basic concepts of chemistry. First, he discusses solids, liquids, and gases. He talks about the general characteristics and particulate-level drawing of each one. Then he lectures on classification of matter, pure substances, mixtures, physical changes, and chemical changes. He ends the lesson with three helpful sample problems. Basic Concepts of Chemistry Chemistry can broadly be defined as the study of matter and its changes. The (3) physical states of matter are solids, liquids and gases. Matter can undergo both physical and chemical changes. Matter can exist as elements, compounds, or as homogeneous and heterogeneous mixtures. Physical properties tend to be measurable and/or related to senses, while chemical properties describe reactivity.