Matter is the fundamental substance of the universe. Scientifically, matter is defined as anything that possesses mass and occupies space (volume). Understanding the distinct characteristics of matter is foundational to all scientific disciplines, from materials engineering to biology. By classifying and measuring how different materials behave, scientists can predict their interactions and harness their potential for countless applications.
Observable Physical Properties
Physical properties are those characteristics of a substance that can be measured or observed without changing the substance’s chemical makeup. These observations might include a substance’s color, odor, density, melting point, or hardness. These properties are separated into two distinct categories: intensive and extensive. This division helps determine which properties are inherent to the material itself and which are simply a measure of its quantity.
Intensive properties are unique to the substance and remain constant regardless of the sample size. For instance, a diamond’s hardness or water’s boiling point of 100 degrees Celsius are the same whether one measures a small drop or a large tank. Density is a prime example of an intensive property, as it represents the fixed ratio of a substance’s mass to its volume. Other intensive properties frequently used for identification include color, temperature, electrical conductivity, and melting point.
Extensive properties, conversely, directly depend on the amount of matter present in the sample. These properties include measurements like mass, volume, and length, which all increase proportionally as the quantity of the substance increases. If a piece of wood is cut in half, both its mass and its volume are reduced by half, demonstrating their dependence on the size of the sample. Extensive properties are helpful for describing a sample but cannot be used alone to identify a substance, unlike intensive properties.
Reactive Chemical Properties
Chemical properties describe a substance’s potential to undergo a chemical reaction and form a new substance. These characteristics can only be observed when the matter is fundamentally altered, meaning the original substance is permanently changed. Unlike a physical change, which might only involve a change of state like melting ice, a chemical change results in the breaking and forming of molecular bonds.
A common chemical property is flammability, which is the ability of a material to ignite or burn when exposed to heat or fire. The process of burning fundamentally transforms the substance into ash, smoke, and gases, illustrating the permanent change in composition. Reactivity, another chemical property, describes how readily a substance will combine chemically with other materials, such as water or oxygen. Highly reactive metals like sodium, for example, will react violently with water, producing heat and hydrogen gas.
Toxicity is also classified as a chemical property, describing the degree to which a substance can cause damage to an organism. This property relates to a substance’s ability to participate in specific chemical reactions within the body that disrupt normal biological processes. The heat of combustion, which is the energy released when a substance burns completely, represents another measurable chemical property. These chemical characteristics are essential for handling materials safely, as they predict a substance’s behavior when introduced to a new chemical environment.
Classification by State
Matter commonly exists in one of four physical states, or phases, which are primarily determined by the energy and arrangement of its constituent particles. These states—solid, liquid, gas, and plasma—govern the substance’s shape, volume, and compressibility. The introduction or removal of energy, often in the form of heat, is responsible for transitions between these distinct phases.
In the solid state, particles are tightly packed together and locked into fixed positions, resulting in a low kinetic energy. This rigid arrangement gives solids a definite shape and a fixed volume that does not easily change. The particles are only able to vibrate in place, which is why solids are generally incompressible and do not flow.
Liquid particles possess more energy, allowing them to remain close together but still move around and slide past one another. This mobility means a liquid has a fixed volume but no definite shape, conforming instead to the shape of its container. Liquids flow easily and are considered a condensed phase because the particles remain in close proximity.
Particles in the gaseous state have significantly higher energy, causing them to be far apart and move freely and randomly at high speeds. Gases have neither a fixed shape nor a fixed volume and will expand to fill any container they occupy. The large amounts of empty space between particles make gases highly compressible.
Plasma is often called the fourth state of matter, existing at extremely high temperatures and possessing the highest energy level. It is similar to a gas, but enough energy has been added to strip electrons from the atoms, creating a mixture of highly charged particles, ions, and free electrons. This ionized gas is the most common form of ordinary matter in the universe, found in stars, lightning, and neon signs.