3.1: Definition We are all familiar with "stuff" - what we call matter. The definition of Matter is anything that has mass and volume (takes up space). For most common objects that we deal with every day, it is fairly simple to demonstrate that they have mass and take up space. You might be able to imagine, however, the difficulty for people several hundred years ago to demonstrate that air has mass and volume. 3.2: States of Matter (Solid, Liquid and Gas) Water can take many forms. At low temperatures (below 0 C ), it is a solid. When at "normal" temperatures (between 0 C and 100 C ), it is a liquid. While at temperatures above 100 C , water is a gas (steam). The state that water is in depends upon the temperature. Each state has its own unique set of physical properties. Matter typically exists in one of three states: solid, liquid, or gas. 3.3: Classification of Matter (Pure Substances and Mixtures) Matter can be classified into two broad categories: pure substances and mixtures. A pure substance is a form of matter that has a constant composition and properties that are constant throughout the sample. A material composed of two or more substances is a mixture. 3.4: Properties of Matter (Chemical and Physical) All matter has physical and chemical properties. Physical properties are characteristics that scientists can measure without changing the composition of the sample under study, such as mass, color, and volume (the amount of space occupied by a sample). Chemical properties describe the characteristic ability of a substance to react to form new substances; they include its flammability and susceptibility to corrosion. 3.5: Changes in Matter (Physical and Chemical) Change is happening all around us all of the time. Just as chemists have classified elements and compounds, they have also classified types of changes. Changes are classified as either physical or chemical changes. Chemists learn a lot about the nature of matter by studying the changes that matter can undergo. Chemists make a distinction between two different types of changes that they study—physical changes and chemical changes. Thumbnail: States of matter for Hebrew Wiktionary. (CC BY-SA 4.0; Enoshd via Wikimedia )