Matter is defined as anything that has mass and takes up space. A property of matter is a characteristic used to describe and distinguish one substance from another. Understanding these properties is foundational in science, providing the framework for identifying, classifying, and predicting how different substances will behave. Properties allow scientists to create a database of characteristics for every element and compound, making it possible to utilize materials effectively.
Properties Based on Amount: Extensive and Intensive
One way to classify the characteristics of a substance is based on whether the property changes with the amount of matter present. Extensive properties are those that depend directly on the quantity of the substance. If you double the size of a sample, the value of its extensive properties will also double.
Examples of extensive properties include mass (the amount of matter in an object), volume (the space it occupies), total energy, and length. Because these properties change with the size of the sample, they are not reliable for identifying an unknown substance.
Intensive properties, in contrast, are independent of the amount of matter present. These characteristics are inherent to the nature of the substance itself, such as its internal structure or composition. The density of pure water, for instance, remains approximately 1 gram per milliliter, whether you measure a single drop or a large tank.
Other examples of intensive properties include temperature, color, melting point, and boiling point. Intensive properties are particularly useful for identification because they remain constant regardless of the sample size. Interestingly, the ratio of two extensive properties, such as mass divided by volume, yields an intensive property like density.
Properties Observed Without Changing Identity: Physical Properties
Physical properties are characteristics that can be observed or measured without changing the substance’s chemical composition. For example, determining the color or density of a metal does not alter the metal itself.
Many physical properties are observable with our senses, such as color, odor, and luster. Others require measurement, including the specific temperatures at which a substance changes state. The melting point is the temperature where a substance transitions from a solid to a liquid, and the boiling point is where it changes from a liquid to a gas.
Other important physical properties include hardness (resistance to being scratched or dented), malleability (the ability to be pressed into thin sheets), and electrical conductivity (the ability to allow electric current to flow). Solubility, the amount of a substance that can dissolve in a solvent, is also a physical property.
Observing physical properties often involves a physical change, which affects the form or appearance but not the molecular identity. When an ice cube melts into liquid water, its shape and physical state change, but the substance remains H2O. Crushing a solid or dissolving salt in water are similar physical changes that leave the chemical composition untouched.
Properties Observed Through Reaction: Chemical Properties
Chemical properties describe a substance’s potential to undergo a change that alters its chemical composition. Unlike physical properties, observing a chemical property always requires a chemical reaction to occur, resulting in the creation of one or more entirely new substances. The new substance will possess a different set of properties than the original material.
A common example is flammability, which is the ability of a substance to burn or ignite. Observing flammability requires the substance to react with oxygen, converting it into different compounds like ash and carbon dioxide. This process changes the fundamental chemical structure of the material.
Reactivity is another broad chemical property, describing the tendency of a substance to combine chemically with other substances. For instance, iron’s reactivity with oxygen and water leads to the formation of rust, which is chemically distinct from pure iron. Acidity and basicity, which describe a substance’s ability to react with acids or bases, are also chemical properties.
The heat of combustion, which is the energy released when a substance burns, is a precise chemical property. Understanding these properties allows scientists to predict how a substance will interact with its environment and other materials.