Electrical conductivity is a physical property of matter, defined as the ability of a substance to transmit an electric current. It measures how easily electric charge carriers, such as electrons or ions, move through a material when an electrical potential difference is applied. Metals have high conductivity, permitting easy flow, while materials like rubber are insulators with very low conductivity.
Defining Physical and Chemical Properties
The distinction between the properties of matter lies in whether the identity of the substance changes during observation. A physical property is a characteristic that can be observed or measured without altering the chemical composition of the substance itself. Examples include observing color, measuring density, or determining the melting point. When ice melts, for instance, it remains water (\(\text{H}_2\text{O}\)), only changing its physical state.
Chemical properties are qualities observed only when the substance undergoes a reaction that changes it into a completely new substance. These properties describe a substance’s potential to react with other materials or to decompose. Flammability is a common example, as burning converts the material into new chemical entities like ash and gas. Reactivity with acids or oxygen, such as iron rusting, also falls under this category because the original substance is consumed to form a new compound.
Justification for Electrical Conductivity as a Physical Property
Electrical conductivity fits the definition of a physical property because the process of conducting electricity does not change the chemical identity of the conductor. When an electric current flows through a metallic conductor like copper wire, the copper atoms remain unchanged. The current consists solely of free-moving valence electrons present in the metal’s lattice structure. These electrons move from atom to atom, but no chemical bonds are broken or formed, and the copper is not transformed into a new substance.
In solutions, such as saltwater or strong electrolytes, the mechanism involves the movement of ions rather than electrons. When an electric field is applied, positively charged ions (cations) move toward the negative electrode, while negatively charged ions (anions) migrate toward the positive electrode. This ionic movement facilitates current flow, but the dissolved salt remains chemically intact. Although electrolysis can occur in some conductive solutions, the general measurement of conductivity itself does not require this chemical change to take place.
Practical Applications and Measurement of Conductivity
Electrical conductivity is measured by determining the reciprocal of a material’s electrical resistivity, which is its opposition to the flow of electric current. Resistivity is typically measured in ohm-meters (\(\Omega \cdot \text{m}\)), meaning conductivity is expressed in Siemens per meter (\(\text{S}/\text{m}\)). Instruments called conductivity meters apply a known alternating electrical current between two electrodes immersed in a substance and measure the resulting voltage.
Conductivity is widely used in environmental science and water treatment to assess water quality and purity. Pure water is a poor conductor, but the presence of dissolved inorganic solids, like salts and minerals, significantly increases its conductivity. Measuring a water sample’s conductivity allows estimation of the concentration of total dissolved solids (TDS), a crucial indicator for drinking water safety. In agriculture, soil conductivity measurements help farmers monitor nutrient and salt concentrations to optimize crop health. The extensive range of conductivities across materials, from copper to quartz, makes this physical property foundational to modern electronics and materials science.