Matter is the fundamental substance of the physical world, defined simply as anything that has mass and occupies space by having volume. Matter exists in various states like solid, liquid, and gas. A property is a distinguishing characteristic that scientists use to describe, identify, and differentiate one type of matter from another.
Categorizing Properties by Amount
Properties are classified based on whether they change with the quantity of the substance present. This system separates properties into two main categories: intensive and extensive. This framework helps scientists select the appropriate characteristics for identifying or measuring a specific sample.
Intensive Properties
Intensive properties remain constant regardless of the sample’s size. These characteristics, which include color, density, and melting point, are intrinsic to the substance itself and independent of its amount. Because they do not change, intensive properties are particularly useful for identifying an unknown substance.
Extensive Properties
Extensive properties are directly dependent on the amount of matter in the sample. Characteristics like mass, volume, and length change proportionally if the sample size is altered. These properties are necessary for measuring the size or quantity of the matter being studied. The ratio of two extensive properties, such as mass divided by volume, often yields an intensive property like density.
Physical Properties
Physical properties can be observed or measured without altering the substance’s underlying chemical identity. They are determined without causing a chemical reaction, meaning the substance remains the same before and after the observation. Even changes in state, such as ice melting into liquid water, are considered physical changes because the chemical structure (\(\text{H}_2\text{O}\)) of the substance is preserved.
Density is an important intensive physical property, defined as the mass per unit volume of a substance. This specific value helps identify a material because it is a fixed ratio that does not change with the sample size. Similarly, the melting point and boiling point are intensive physical properties, representing the precise temperatures at which a substance transitions between solid, liquid, and gas states.
Other characteristics describe a substance’s mechanical behavior, such as hardness (resistance to scratching or deformation). Malleability and ductility are also intensive properties that describe a material’s ability to be shaped. Malleability is the capacity to be hammered or rolled into thin sheets, like aluminum foil, while ductility is the capacity to be drawn out into a thin wire, which is common in metals like copper. Extensive physical properties, such as mass and volume, are essential for quantifying the amount of matter.
Chemical Properties
Chemical properties describe a substance’s potential to undergo a change that transforms it into a new and different substance. Observing a chemical property always involves a chemical reaction that alters the substance’s molecular structure. This means the original matter is consumed, and a new product with entirely different properties is formed.
Flammability is a prominent chemical property, describing the ability of a material to burn or ignite when exposed to a flame. Combustion is a chemical change where the original substance reacts rapidly with oxygen, producing new compounds like ash, carbon dioxide, and water vapor. The heat of combustion is a related property, quantifying the amount of energy released during this burning process.
Reactivity is a broad chemical property that defines how easily a substance will participate in a chemical change with other materials. For example, iron displays reactivity with oxygen in the presence of moisture, which results in the formation of iron oxide, commonly known as rust. Toxicity is another chemical property, describing a substance’s ability to cause damage to a living organism by interfering with biological processes through chemical reactions. The oxidation state of an element, which relates to its tendency to gain or lose electrons, is a specific chemical property that governs how it will react in different environments.