Conductivity, the ability of a material to transmit heat or electric current, is not classified as a chemical property. It is definitively a physical property of matter. This distinction is based on how the property is observed and measured, which in the case of conductivity, does not alter the fundamental chemical identity of the substance being tested.
How Properties of Matter Are Classified
Scientists classify the characteristics of matter into two main categories to better understand and predict their behavior: physical properties and chemical properties. A physical property is any characteristic that can be observed or measured without changing the substance’s chemical composition. Examples include qualities like color, density, melting point, and shape. Measuring a physical property may cause a temporary physical change, but the substance’s molecular structure remains the same. Conversely, a chemical property describes a substance’s potential to undergo a specific chemical change or reaction. Observing a chemical property always results in the formation of a new substance with a different chemical formula.
Why Conductivity is a Physical Property
Conductivity is classified as a physical property because its measurement does not require or cause a change in the material’s internal atomic structure. When a copper wire carries an electric current, the electrons are simply moving through the established lattice of copper atoms. The copper atoms themselves remain chemically unaltered, meaning the wire is still composed of copper before and after the electricity passes through it.
This principle applies to both electrical conductivity, which is the flow of electrons, and thermal conductivity, which is the transfer of heat energy. In both cases, the substance’s chemical makeup remains constant throughout the process. Observing the ability to conduct electricity is similar to observing the material’s density or melting point; the observation itself leaves the substance unchanged. When thermal conductivity is measured, the atoms vibrate more quickly to pass energy along, but no chemical bonds are broken or formed.
Examples of True Chemical Properties
In contrast to conductivity, a true chemical property can only be observed by performing a chemical reaction that changes the substance into a new material. Flammability is a prime example, as determining a substance’s ability to burn requires combustion, which converts the original material into different substances like ash and carbon dioxide. The original chemical composition is lost in the process.
Reactivity is another chemical property, describing a substance’s potential to interact with other chemicals, such as acid or oxygen, to form a new compound. For instance, the property of iron to form rust is an example of chemical reactivity with oxygen and water, creating a new substance called iron oxide. Toxicity is also a chemical property, as it describes the adverse chemical reaction the substance can cause.