Matter is defined as anything that possesses mass and occupies space, making up everything from the air we breathe to distant stars. Describing matter requires relying on measurable qualities to distinguish one substance from another. These properties allow scientists to characterize, classify, and predict how different materials will behave.
Defining Matter and Its Core Components
A substance is considered matter if it possesses mass and occupies volume. Mass is a measure of the amount of substance present in an object, which is distinct from weight, the measure of the gravitational force acting on that mass. A person’s mass remains constant whether they are on Earth or the moon, while their weight changes dramatically due to the difference in gravity. Volume describes the amount of space an object takes up. All matter is ultimately composed of atoms, which combine to form molecules, such as water (H₂O).
Describing Matter through Physical Properties
Physical properties are characteristics that can be observed or measured without altering the substance’s chemical identity. These properties are used to identify or classify materials because their measurement does not produce a new substance. For example, observing that water is colorless or measuring its boiling point are physical properties, as the water remains H₂O throughout the process.
Physical properties are categorized based on whether they depend on the amount of matter present. Extensive properties, such as mass and volume, change with the size of the sample. A larger piece of material will have a greater mass and volume than a smaller piece.
Intensive properties remain the same regardless of the sample size, making them effective for identifying an unknown substance. Density, the ratio of mass to volume, is an intensive property; a drop of pure water and a swimming pool of pure water share the same density. Other intensive properties include color, odor, hardness, and the temperatures at which a substance melts or boils. Measuring the melting point confirms a substance’s identity, irrespective of the sample size.
Describing Matter through Chemical Properties
Chemical properties describe a substance’s potential to undergo a chemical reaction and transform into a new substance. These characteristics are only observed when the material’s molecular composition is changed. Unlike physical properties, chemical properties involve a fundamental alteration of the substance’s structure.
Flammability is a chemical property describing a material’s ability to combust or burn in the presence of oxygen, resulting in entirely new substances like ash and smoke. Reactivity describes how easily a substance will combine chemically with other materials. The rusting of iron is a common example of reactivity, where iron combines with oxygen in the air to form iron oxide, a compound with a completely different composition and characteristics.
Toxicity, the extent to which a chemical can harm an organism, is another chemical property, as it relates to the substance’s ability to react with biological molecules. The observation that pure copper dissolves in dilute nitric acid to produce a blue solution and brown gas demonstrates its chemical property of reactivity with acids. These properties define the chemical stability or instability of a substance.
The Three Common States
Matter is described by its physical state, which is determined by the arrangement and energy of its constituent particles. The three most common states encountered are solid, liquid, and gas. These states are not fixed for a given substance and can transition between one another through physical changes.
A solid is characterized by particles that are tightly packed and held in fixed positions, allowing them only to vibrate. This arrangement gives the substance a definite shape and a fixed volume. Liquids have particles that remain close together but move past one another, maintaining a fixed volume but adopting the shape of their container. Gases consist of particles that are widely separated and move freely at high speeds, allowing them to expand to fill the entire volume of any container. Changes between these states, such as melting (solid to liquid) or boiling (liquid to gas), are physical changes because the substance’s molecular composition does not change.